## Create a Message

`BetaMessage beta().messages().create(MessageCreateParamsparams, RequestOptionsrequestOptions = RequestOptions.none())`

**post** `/v1/messages`

Send a structured list of input messages with text and/or image content, and the model will generate the next message in the conversation.

The Messages API can be used for either single queries or stateless multi-turn conversations.

Learn more about the Messages API in our [user guide](https://docs.claude.com/en/docs/initial-setup)

### Parameters

- `MessageCreateParams params`

  - `Optional<List<AnthropicBeta>> betas`

    Optional header to specify the beta version(s) you want to use.

    - `MESSAGE_BATCHES_2024_09_24("message-batches-2024-09-24")`

    - `PROMPT_CACHING_2024_07_31("prompt-caching-2024-07-31")`

    - `COMPUTER_USE_2024_10_22("computer-use-2024-10-22")`

    - `COMPUTER_USE_2025_01_24("computer-use-2025-01-24")`

    - `PDFS_2024_09_25("pdfs-2024-09-25")`

    - `TOKEN_COUNTING_2024_11_01("token-counting-2024-11-01")`

    - `TOKEN_EFFICIENT_TOOLS_2025_02_19("token-efficient-tools-2025-02-19")`

    - `OUTPUT_128K_2025_02_19("output-128k-2025-02-19")`

    - `FILES_API_2025_04_14("files-api-2025-04-14")`

    - `MCP_CLIENT_2025_04_04("mcp-client-2025-04-04")`

    - `MCP_CLIENT_2025_11_20("mcp-client-2025-11-20")`

    - `DEV_FULL_THINKING_2025_05_14("dev-full-thinking-2025-05-14")`

    - `INTERLEAVED_THINKING_2025_05_14("interleaved-thinking-2025-05-14")`

    - `CODE_EXECUTION_2025_05_22("code-execution-2025-05-22")`

    - `EXTENDED_CACHE_TTL_2025_04_11("extended-cache-ttl-2025-04-11")`

    - `CONTEXT_1M_2025_08_07("context-1m-2025-08-07")`

    - `CONTEXT_MANAGEMENT_2025_06_27("context-management-2025-06-27")`

    - `MODEL_CONTEXT_WINDOW_EXCEEDED_2025_08_26("model-context-window-exceeded-2025-08-26")`

    - `SKILLS_2025_10_02("skills-2025-10-02")`

    - `FAST_MODE_2026_02_01("fast-mode-2026-02-01")`

    - `OUTPUT_300K_2026_03_24("output-300k-2026-03-24")`

    - `USER_PROFILES_2026_03_24("user-profiles-2026-03-24")`

    - `ADVISOR_TOOL_2026_03_01("advisor-tool-2026-03-01")`

    - `MANAGED_AGENTS_2026_04_01("managed-agents-2026-04-01")`

    - `CACHE_DIAGNOSIS_2026_04_07("cache-diagnosis-2026-04-07")`

    - `THINKING_TOKEN_COUNT_2026_05_13("thinking-token-count-2026-05-13")`

    - `SERVER_SIDE_FALLBACK_2026_06_01("server-side-fallback-2026-06-01")`

    - `FALLBACK_CREDIT_2026_06_01("fallback-credit-2026-06-01")`

  - `long maxTokens`

    The maximum number of tokens to generate before stopping.

    Note that our models may stop _before_ reaching this maximum. This parameter only specifies the absolute maximum number of tokens to generate.

    Set to `0` to populate the [prompt cache](https://docs.claude.com/en/docs/build-with-claude/prompt-caching#pre-warming-the-cache) without generating a response.

    Different models have different maximum values for this parameter.  See [models](https://docs.claude.com/en/docs/models-overview) for details.

  - `List<BetaMessageParam> messages`

    Input messages.

    Our models are trained to operate on alternating `user` and `assistant` conversational turns. When creating a new `Message`, you specify the prior conversational turns with the `messages` parameter, and the model then generates the next `Message` in the conversation. Consecutive `user` or `assistant` turns in your request will be combined into a single turn.

    Each input message must be an object with a `role` and `content`. You can specify a single `user`-role message, or you can include multiple `user` and `assistant` messages.

    If the final message uses the `assistant` role, the response content will continue immediately from the content in that message. This can be used to constrain part of the model's response.

    Example with a single `user` message:

    ```json
    [{"role": "user", "content": "Hello, Claude"}]
    ```

    Example with multiple conversational turns:

    ```json
    [
      {"role": "user", "content": "Hello there."},
      {"role": "assistant", "content": "Hi, I'm Claude. How can I help you?"},
      {"role": "user", "content": "Can you explain LLMs in plain English?"},
    ]
    ```

    Example with a partially-filled response from Claude:

    ```json
    [
      {"role": "user", "content": "What's the Greek name for Sun? (A) Sol (B) Helios (C) Sun"},
      {"role": "assistant", "content": "The best answer is ("},
    ]
    ```

    Each input message `content` may be either a single `string` or an array of content blocks, where each block has a specific `type`. Using a `string` for `content` is shorthand for an array of one content block of type `"text"`. The following input messages are equivalent:

    ```json
    {"role": "user", "content": "Hello, Claude"}
    ```

    ```json
    {"role": "user", "content": [{"type": "text", "text": "Hello, Claude"}]}
    ```

    See [input examples](https://docs.claude.com/en/api/messages-examples).

    Note that if you want to include a [system prompt](https://docs.claude.com/en/docs/system-prompts), you can use the top-level `system` parameter — there is no `"system"` role for input messages in the Messages API.

    There is a limit of 100,000 messages in a single request.

    - `Content content`

      - `String`

      - `List<BetaContentBlockParam>`

        - `class BetaTextBlockParam:`

          - `String text`

          - `JsonValue; type "text"constant`

            - `TEXT("text")`

          - `Optional<BetaCacheControlEphemeral> cacheControl`

            Create a cache control breakpoint at this content block.

            - `JsonValue; type "ephemeral"constant`

              - `EPHEMERAL("ephemeral")`

            - `Optional<Ttl> ttl`

              The time-to-live for the cache control breakpoint.

              This may be one the following values:

              - `5m`: 5 minutes
              - `1h`: 1 hour

              Defaults to `5m`.

              - `TTL_5M("5m")`

              - `TTL_1H("1h")`

          - `Optional<List<BetaTextCitationParam>> citations`

            - `class BetaCitationCharLocationParam:`

              - `String citedText`

              - `long documentIndex`

              - `Optional<String> documentTitle`

              - `long endCharIndex`

              - `long startCharIndex`

              - `JsonValue; type "char_location"constant`

                - `CHAR_LOCATION("char_location")`

            - `class BetaCitationPageLocationParam:`

              - `String citedText`

              - `long documentIndex`

              - `Optional<String> documentTitle`

              - `long endPageNumber`

              - `long startPageNumber`

              - `JsonValue; type "page_location"constant`

                - `PAGE_LOCATION("page_location")`

            - `class BetaCitationContentBlockLocationParam:`

              - `String citedText`

                The full text of the cited block range, concatenated.

                Always equals the contents of `content[start_block_index:end_block_index]` joined together. The text block is the minimal citable unit; this field is never a substring of a single block. Not counted toward output tokens, and not counted toward input tokens when sent back in subsequent turns.

              - `long documentIndex`

              - `Optional<String> documentTitle`

              - `long endBlockIndex`

                Exclusive 0-based end index of the cited block range in the source's `content` array.

                Always greater than `start_block_index`; a single-block citation has `end_block_index = start_block_index + 1`.

              - `long startBlockIndex`

                0-based index of the first cited block in the source's `content` array.

              - `JsonValue; type "content_block_location"constant`

                - `CONTENT_BLOCK_LOCATION("content_block_location")`

            - `class BetaCitationWebSearchResultLocationParam:`

              - `String citedText`

              - `String encryptedIndex`

              - `Optional<String> title`

              - `JsonValue; type "web_search_result_location"constant`

                - `WEB_SEARCH_RESULT_LOCATION("web_search_result_location")`

              - `String url`

            - `class BetaCitationSearchResultLocationParam:`

              - `String citedText`

                The full text of the cited block range, concatenated.

                Always equals the contents of `content[start_block_index:end_block_index]` joined together. The text block is the minimal citable unit; this field is never a substring of a single block. Not counted toward output tokens, and not counted toward input tokens when sent back in subsequent turns.

              - `long endBlockIndex`

                Exclusive 0-based end index of the cited block range in the source's `content` array.

                Always greater than `start_block_index`; a single-block citation has `end_block_index = start_block_index + 1`.

              - `long searchResultIndex`

                0-based index of the cited search result among all `search_result` content blocks in the request, in the order they appear across messages and tool results.

                Counted separately from `document_index`; server-side web search results are not included in this count.

              - `String source`

              - `long startBlockIndex`

                0-based index of the first cited block in the source's `content` array.

              - `Optional<String> title`

              - `JsonValue; type "search_result_location"constant`

                - `SEARCH_RESULT_LOCATION("search_result_location")`

        - `class BetaImageBlockParam:`

          - `Source source`

            - `class BetaBase64ImageSource:`

              - `String data`

              - `MediaType mediaType`

                - `IMAGE_JPEG("image/jpeg")`

                - `IMAGE_PNG("image/png")`

                - `IMAGE_GIF("image/gif")`

                - `IMAGE_WEBP("image/webp")`

              - `JsonValue; type "base64"constant`

                - `BASE64("base64")`

            - `class BetaUrlImageSource:`

              - `JsonValue; type "url"constant`

                - `URL("url")`

              - `String url`

            - `class BetaFileImageSource:`

              - `String fileId`

              - `JsonValue; type "file"constant`

                - `FILE("file")`

          - `JsonValue; type "image"constant`

            - `IMAGE("image")`

          - `Optional<BetaCacheControlEphemeral> cacheControl`

            Create a cache control breakpoint at this content block.

        - `class BetaRequestDocumentBlock:`

          - `Source source`

            - `class BetaBase64PdfSource:`

              - `String data`

              - `JsonValue; mediaType "application/pdf"constant`

                - `APPLICATION_PDF("application/pdf")`

              - `JsonValue; type "base64"constant`

                - `BASE64("base64")`

            - `class BetaPlainTextSource:`

              - `String data`

              - `JsonValue; mediaType "text/plain"constant`

                - `TEXT_PLAIN("text/plain")`

              - `JsonValue; type "text"constant`

                - `TEXT("text")`

            - `class BetaContentBlockSource:`

              - `Content content`

                - `String`

                - `List<BetaContentBlockSourceContent>`

                  - `class BetaTextBlockParam:`

                  - `class BetaImageBlockParam:`

              - `JsonValue; type "content"constant`

                - `CONTENT("content")`

            - `class BetaUrlPdfSource:`

              - `JsonValue; type "url"constant`

                - `URL("url")`

              - `String url`

            - `class BetaFileDocumentSource:`

              - `String fileId`

              - `JsonValue; type "file"constant`

                - `FILE("file")`

          - `JsonValue; type "document"constant`

            - `DOCUMENT("document")`

          - `Optional<BetaCacheControlEphemeral> cacheControl`

            Create a cache control breakpoint at this content block.

          - `Optional<BetaCitationsConfigParam> citations`

            - `Optional<Boolean> enabled`

          - `Optional<String> context`

          - `Optional<String> title`

        - `class BetaSearchResultBlockParam:`

          - `List<BetaTextBlockParam> content`

            - `String text`

            - `JsonValue; type "text"constant`

            - `Optional<BetaCacheControlEphemeral> cacheControl`

              Create a cache control breakpoint at this content block.

            - `Optional<List<BetaTextCitationParam>> citations`

          - `String source`

          - `String title`

          - `JsonValue; type "search_result"constant`

            - `SEARCH_RESULT("search_result")`

          - `Optional<BetaCacheControlEphemeral> cacheControl`

            Create a cache control breakpoint at this content block.

          - `Optional<BetaCitationsConfigParam> citations`

        - `class BetaThinkingBlockParam:`

          - `String signature`

          - `String thinking`

          - `JsonValue; type "thinking"constant`

            - `THINKING("thinking")`

        - `class BetaRedactedThinkingBlockParam:`

          - `String data`

          - `JsonValue; type "redacted_thinking"constant`

            - `REDACTED_THINKING("redacted_thinking")`

        - `class BetaToolUseBlockParam:`

          - `String id`

          - `Input input`

          - `String name`

          - `JsonValue; type "tool_use"constant`

            - `TOOL_USE("tool_use")`

          - `Optional<BetaCacheControlEphemeral> cacheControl`

            Create a cache control breakpoint at this content block.

          - `Optional<Caller> caller`

            Tool invocation directly from the model.

            - `class BetaDirectCaller:`

              Tool invocation directly from the model.

              - `JsonValue; type "direct"constant`

                - `DIRECT("direct")`

            - `class BetaServerToolCaller:`

              Tool invocation generated by a server-side tool.

              - `String toolId`

              - `JsonValue; type "code_execution_20250825"constant`

                - `CODE_EXECUTION_20250825("code_execution_20250825")`

            - `class BetaServerToolCaller20260120:`

              - `String toolId`

              - `JsonValue; type "code_execution_20260120"constant`

                - `CODE_EXECUTION_20260120("code_execution_20260120")`

        - `class BetaToolResultBlockParam:`

          - `String toolUseId`

          - `JsonValue; type "tool_result"constant`

            - `TOOL_RESULT("tool_result")`

          - `Optional<BetaCacheControlEphemeral> cacheControl`

            Create a cache control breakpoint at this content block.

          - `Optional<Content> content`

            - `String`

            - `List<Block>`

              - `class BetaTextBlockParam:`

              - `class BetaImageBlockParam:`

              - `class BetaSearchResultBlockParam:`

              - `class BetaRequestDocumentBlock:`

              - `class BetaToolReferenceBlockParam:`

                Tool reference block that can be included in tool_result content.

                - `String toolName`

                - `JsonValue; type "tool_reference"constant`

                  - `TOOL_REFERENCE("tool_reference")`

                - `Optional<BetaCacheControlEphemeral> cacheControl`

                  Create a cache control breakpoint at this content block.

          - `Optional<Boolean> isError`

        - `class BetaServerToolUseBlockParam:`

          - `String id`

          - `Input input`

          - `Name name`

            - `ADVISOR("advisor")`

            - `WEB_SEARCH("web_search")`

            - `WEB_FETCH("web_fetch")`

            - `CODE_EXECUTION("code_execution")`

            - `BASH_CODE_EXECUTION("bash_code_execution")`

            - `TEXT_EDITOR_CODE_EXECUTION("text_editor_code_execution")`

            - `TOOL_SEARCH_TOOL_REGEX("tool_search_tool_regex")`

            - `TOOL_SEARCH_TOOL_BM25("tool_search_tool_bm25")`

          - `JsonValue; type "server_tool_use"constant`

            - `SERVER_TOOL_USE("server_tool_use")`

          - `Optional<BetaCacheControlEphemeral> cacheControl`

            Create a cache control breakpoint at this content block.

          - `Optional<Caller> caller`

            Tool invocation directly from the model.

            - `class BetaDirectCaller:`

              Tool invocation directly from the model.

            - `class BetaServerToolCaller:`

              Tool invocation generated by a server-side tool.

            - `class BetaServerToolCaller20260120:`

        - `class BetaWebSearchToolResultBlockParam:`

          - `BetaWebSearchToolResultBlockParamContent content`

            - `List<BetaWebSearchResultBlockParam>`

              - `String encryptedContent`

              - `String title`

              - `JsonValue; type "web_search_result"constant`

                - `WEB_SEARCH_RESULT("web_search_result")`

              - `String url`

              - `Optional<String> pageAge`

            - `class BetaWebSearchToolRequestError:`

              - `BetaWebSearchToolResultErrorCode errorCode`

                - `INVALID_TOOL_INPUT("invalid_tool_input")`

                - `UNAVAILABLE("unavailable")`

                - `MAX_USES_EXCEEDED("max_uses_exceeded")`

                - `TOO_MANY_REQUESTS("too_many_requests")`

                - `QUERY_TOO_LONG("query_too_long")`

                - `REQUEST_TOO_LARGE("request_too_large")`

              - `JsonValue; type "web_search_tool_result_error"constant`

                - `WEB_SEARCH_TOOL_RESULT_ERROR("web_search_tool_result_error")`

          - `String toolUseId`

          - `JsonValue; type "web_search_tool_result"constant`

            - `WEB_SEARCH_TOOL_RESULT("web_search_tool_result")`

          - `Optional<BetaCacheControlEphemeral> cacheControl`

            Create a cache control breakpoint at this content block.

          - `Optional<Caller> caller`

            Tool invocation directly from the model.

            - `class BetaDirectCaller:`

              Tool invocation directly from the model.

            - `class BetaServerToolCaller:`

              Tool invocation generated by a server-side tool.

            - `class BetaServerToolCaller20260120:`

        - `class BetaWebFetchToolResultBlockParam:`

          - `Content content`

            - `class BetaWebFetchToolResultErrorBlockParam:`

              - `BetaWebFetchToolResultErrorCode errorCode`

                - `INVALID_TOOL_INPUT("invalid_tool_input")`

                - `URL_TOO_LONG("url_too_long")`

                - `URL_NOT_ALLOWED("url_not_allowed")`

                - `URL_NOT_IN_PRIOR_CONTEXT("url_not_in_prior_context")`

                - `URL_NOT_ACCESSIBLE("url_not_accessible")`

                - `UNSUPPORTED_CONTENT_TYPE("unsupported_content_type")`

                - `TOO_MANY_REQUESTS("too_many_requests")`

                - `MAX_USES_EXCEEDED("max_uses_exceeded")`

                - `UNAVAILABLE("unavailable")`

              - `JsonValue; type "web_fetch_tool_result_error"constant`

                - `WEB_FETCH_TOOL_RESULT_ERROR("web_fetch_tool_result_error")`

            - `class BetaWebFetchBlockParam:`

              - `BetaRequestDocumentBlock content`

              - `JsonValue; type "web_fetch_result"constant`

                - `WEB_FETCH_RESULT("web_fetch_result")`

              - `String url`

                Fetched content URL

              - `Optional<String> retrievedAt`

                ISO 8601 timestamp when the content was retrieved

          - `String toolUseId`

          - `JsonValue; type "web_fetch_tool_result"constant`

            - `WEB_FETCH_TOOL_RESULT("web_fetch_tool_result")`

          - `Optional<BetaCacheControlEphemeral> cacheControl`

            Create a cache control breakpoint at this content block.

          - `Optional<Caller> caller`

            Tool invocation directly from the model.

            - `class BetaDirectCaller:`

              Tool invocation directly from the model.

            - `class BetaServerToolCaller:`

              Tool invocation generated by a server-side tool.

            - `class BetaServerToolCaller20260120:`

        - `class BetaAdvisorToolResultBlockParam:`

          - `Content content`

            - `class BetaAdvisorToolResultErrorParam:`

              - `ErrorCode errorCode`

                - `MAX_USES_EXCEEDED("max_uses_exceeded")`

                - `PROMPT_TOO_LONG("prompt_too_long")`

                - `TOO_MANY_REQUESTS("too_many_requests")`

                - `OVERLOADED("overloaded")`

                - `UNAVAILABLE("unavailable")`

                - `EXECUTION_TIME_EXCEEDED("execution_time_exceeded")`

                - `MODEL_NOT_FOUND("model_not_found")`

              - `JsonValue; type "advisor_tool_result_error"constant`

                - `ADVISOR_TOOL_RESULT_ERROR("advisor_tool_result_error")`

            - `class BetaAdvisorResultBlockParam:`

              - `String text`

              - `JsonValue; type "advisor_result"constant`

                - `ADVISOR_RESULT("advisor_result")`

              - `Optional<String> stopReason`

            - `class BetaAdvisorRedactedResultBlockParam:`

              - `String encryptedContent`

                Opaque blob produced by a prior response; must be round-tripped verbatim.

              - `JsonValue; type "advisor_redacted_result"constant`

                - `ADVISOR_REDACTED_RESULT("advisor_redacted_result")`

              - `Optional<String> stopReason`

          - `String toolUseId`

          - `JsonValue; type "advisor_tool_result"constant`

            - `ADVISOR_TOOL_RESULT("advisor_tool_result")`

          - `Optional<BetaCacheControlEphemeral> cacheControl`

            Create a cache control breakpoint at this content block.

        - `class BetaCodeExecutionToolResultBlockParam:`

          - `BetaCodeExecutionToolResultBlockParamContent content`

            Code execution result with encrypted stdout for PFC + web_search results.

            - `class BetaCodeExecutionToolResultErrorParam:`

              - `BetaCodeExecutionToolResultErrorCode errorCode`

                - `INVALID_TOOL_INPUT("invalid_tool_input")`

                - `UNAVAILABLE("unavailable")`

                - `TOO_MANY_REQUESTS("too_many_requests")`

                - `EXECUTION_TIME_EXCEEDED("execution_time_exceeded")`

              - `JsonValue; type "code_execution_tool_result_error"constant`

                - `CODE_EXECUTION_TOOL_RESULT_ERROR("code_execution_tool_result_error")`

            - `class BetaCodeExecutionResultBlockParam:`

              - `List<BetaCodeExecutionOutputBlockParam> content`

                - `String fileId`

                - `JsonValue; type "code_execution_output"constant`

                  - `CODE_EXECUTION_OUTPUT("code_execution_output")`

              - `long returnCode`

              - `String stderr`

              - `String stdout`

              - `JsonValue; type "code_execution_result"constant`

                - `CODE_EXECUTION_RESULT("code_execution_result")`

            - `class BetaEncryptedCodeExecutionResultBlockParam:`

              Code execution result with encrypted stdout for PFC + web_search results.

              - `List<BetaCodeExecutionOutputBlockParam> content`

                - `String fileId`

                - `JsonValue; type "code_execution_output"constant`

              - `String encryptedStdout`

              - `long returnCode`

              - `String stderr`

              - `JsonValue; type "encrypted_code_execution_result"constant`

                - `ENCRYPTED_CODE_EXECUTION_RESULT("encrypted_code_execution_result")`

          - `String toolUseId`

          - `JsonValue; type "code_execution_tool_result"constant`

            - `CODE_EXECUTION_TOOL_RESULT("code_execution_tool_result")`

          - `Optional<BetaCacheControlEphemeral> cacheControl`

            Create a cache control breakpoint at this content block.

        - `class BetaBashCodeExecutionToolResultBlockParam:`

          - `Content content`

            - `class BetaBashCodeExecutionToolResultErrorParam:`

              - `ErrorCode errorCode`

                - `INVALID_TOOL_INPUT("invalid_tool_input")`

                - `UNAVAILABLE("unavailable")`

                - `TOO_MANY_REQUESTS("too_many_requests")`

                - `EXECUTION_TIME_EXCEEDED("execution_time_exceeded")`

                - `OUTPUT_FILE_TOO_LARGE("output_file_too_large")`

              - `JsonValue; type "bash_code_execution_tool_result_error"constant`

                - `BASH_CODE_EXECUTION_TOOL_RESULT_ERROR("bash_code_execution_tool_result_error")`

            - `class BetaBashCodeExecutionResultBlockParam:`

              - `List<BetaBashCodeExecutionOutputBlockParam> content`

                - `String fileId`

                - `JsonValue; type "bash_code_execution_output"constant`

                  - `BASH_CODE_EXECUTION_OUTPUT("bash_code_execution_output")`

              - `long returnCode`

              - `String stderr`

              - `String stdout`

              - `JsonValue; type "bash_code_execution_result"constant`

                - `BASH_CODE_EXECUTION_RESULT("bash_code_execution_result")`

          - `String toolUseId`

          - `JsonValue; type "bash_code_execution_tool_result"constant`

            - `BASH_CODE_EXECUTION_TOOL_RESULT("bash_code_execution_tool_result")`

          - `Optional<BetaCacheControlEphemeral> cacheControl`

            Create a cache control breakpoint at this content block.

        - `class BetaTextEditorCodeExecutionToolResultBlockParam:`

          - `Content content`

            - `class BetaTextEditorCodeExecutionToolResultErrorParam:`

              - `ErrorCode errorCode`

                - `INVALID_TOOL_INPUT("invalid_tool_input")`

                - `UNAVAILABLE("unavailable")`

                - `TOO_MANY_REQUESTS("too_many_requests")`

                - `EXECUTION_TIME_EXCEEDED("execution_time_exceeded")`

                - `FILE_NOT_FOUND("file_not_found")`

              - `JsonValue; type "text_editor_code_execution_tool_result_error"constant`

                - `TEXT_EDITOR_CODE_EXECUTION_TOOL_RESULT_ERROR("text_editor_code_execution_tool_result_error")`

              - `Optional<String> errorMessage`

            - `class BetaTextEditorCodeExecutionViewResultBlockParam:`

              - `String content`

              - `FileType fileType`

                - `TEXT("text")`

                - `IMAGE("image")`

                - `PDF("pdf")`

              - `JsonValue; type "text_editor_code_execution_view_result"constant`

                - `TEXT_EDITOR_CODE_EXECUTION_VIEW_RESULT("text_editor_code_execution_view_result")`

              - `Optional<Long> numLines`

              - `Optional<Long> startLine`

              - `Optional<Long> totalLines`

            - `class BetaTextEditorCodeExecutionCreateResultBlockParam:`

              - `boolean isFileUpdate`

              - `JsonValue; type "text_editor_code_execution_create_result"constant`

                - `TEXT_EDITOR_CODE_EXECUTION_CREATE_RESULT("text_editor_code_execution_create_result")`

            - `class BetaTextEditorCodeExecutionStrReplaceResultBlockParam:`

              - `JsonValue; type "text_editor_code_execution_str_replace_result"constant`

                - `TEXT_EDITOR_CODE_EXECUTION_STR_REPLACE_RESULT("text_editor_code_execution_str_replace_result")`

              - `Optional<List<String>> lines`

              - `Optional<Long> newLines`

              - `Optional<Long> newStart`

              - `Optional<Long> oldLines`

              - `Optional<Long> oldStart`

          - `String toolUseId`

          - `JsonValue; type "text_editor_code_execution_tool_result"constant`

            - `TEXT_EDITOR_CODE_EXECUTION_TOOL_RESULT("text_editor_code_execution_tool_result")`

          - `Optional<BetaCacheControlEphemeral> cacheControl`

            Create a cache control breakpoint at this content block.

        - `class BetaToolSearchToolResultBlockParam:`

          - `Content content`

            - `class BetaToolSearchToolResultErrorParam:`

              - `ErrorCode errorCode`

                - `INVALID_TOOL_INPUT("invalid_tool_input")`

                - `UNAVAILABLE("unavailable")`

                - `TOO_MANY_REQUESTS("too_many_requests")`

                - `EXECUTION_TIME_EXCEEDED("execution_time_exceeded")`

              - `JsonValue; type "tool_search_tool_result_error"constant`

                - `TOOL_SEARCH_TOOL_RESULT_ERROR("tool_search_tool_result_error")`

              - `Optional<String> errorMessage`

            - `class BetaToolSearchToolSearchResultBlockParam:`

              - `List<BetaToolReferenceBlockParam> toolReferences`

                - `String toolName`

                - `JsonValue; type "tool_reference"constant`

                - `Optional<BetaCacheControlEphemeral> cacheControl`

                  Create a cache control breakpoint at this content block.

              - `JsonValue; type "tool_search_tool_search_result"constant`

                - `TOOL_SEARCH_TOOL_SEARCH_RESULT("tool_search_tool_search_result")`

          - `String toolUseId`

          - `JsonValue; type "tool_search_tool_result"constant`

            - `TOOL_SEARCH_TOOL_RESULT("tool_search_tool_result")`

          - `Optional<BetaCacheControlEphemeral> cacheControl`

            Create a cache control breakpoint at this content block.

        - `class BetaMcpToolUseBlockParam:`

          - `String id`

          - `Input input`

          - `String name`

          - `String serverName`

            The name of the MCP server

          - `JsonValue; type "mcp_tool_use"constant`

            - `MCP_TOOL_USE("mcp_tool_use")`

          - `Optional<BetaCacheControlEphemeral> cacheControl`

            Create a cache control breakpoint at this content block.

        - `class BetaRequestMcpToolResultBlockParam:`

          - `String toolUseId`

          - `JsonValue; type "mcp_tool_result"constant`

            - `MCP_TOOL_RESULT("mcp_tool_result")`

          - `Optional<BetaCacheControlEphemeral> cacheControl`

            Create a cache control breakpoint at this content block.

          - `Optional<Content> content`

            - `String`

            - `List<BetaTextBlockParam>`

              - `String text`

              - `JsonValue; type "text"constant`

              - `Optional<BetaCacheControlEphemeral> cacheControl`

                Create a cache control breakpoint at this content block.

              - `Optional<List<BetaTextCitationParam>> citations`

          - `Optional<Boolean> isError`

        - `class BetaContainerUploadBlockParam:`

          A content block that represents a file to be uploaded to the container
          Files uploaded via this block will be available in the container's input directory.

          - `String fileId`

          - `JsonValue; type "container_upload"constant`

            - `CONTAINER_UPLOAD("container_upload")`

          - `Optional<BetaCacheControlEphemeral> cacheControl`

            Create a cache control breakpoint at this content block.

        - `class BetaCompactionBlockParam:`

          A compaction block containing summary of previous context.

          Users should round-trip these blocks from responses to subsequent requests
          to maintain context across compaction boundaries.

          When content is None, the block represents a failed compaction. The server
          treats these as no-ops. Empty string content is not allowed.

          - `JsonValue; type "compaction"constant`

            - `COMPACTION("compaction")`

          - `Optional<BetaCacheControlEphemeral> cacheControl`

            Create a cache control breakpoint at this content block.

          - `Optional<String> content`

            Summary of previously compacted content, or null if compaction failed

          - `Optional<String> encryptedContent`

            Opaque metadata from prior compaction, to be round-tripped verbatim

        - `class BetaMidConversationSystemBlockParam:`

          System instructions that appear mid-conversation.

          Use this block to provide or update system-level instructions at a specific
          point in the conversation, rather than only via the top-level `system` parameter.

          - `List<BetaTextBlockParam> content`

            System instruction text blocks.

            - `String text`

            - `JsonValue; type "text"constant`

            - `Optional<BetaCacheControlEphemeral> cacheControl`

              Create a cache control breakpoint at this content block.

            - `Optional<List<BetaTextCitationParam>> citations`

          - `JsonValue; type "mid_conv_system"constant`

            - `MID_CONV_SYSTEM("mid_conv_system")`

          - `Optional<BetaCacheControlEphemeral> cacheControl`

            Create a cache control breakpoint at this content block.

        - `class BetaFallbackBlockParam:`

          A `fallback` block echoed back from a prior response.

          Accepted in `messages[].content` and never rendered into the prompt,
          not validated against the request's `fallbacks` chain or top-level
          `model`, and stripped before the sticky-routing cache key is computed.

          Callers should echo the assistant turn verbatim — block included. The
          block's position is load-bearing for thinking verification: the thinking
          runs on either side of a fallback hop carry independently-rooted
          verification hash chains, and this block is the only record of where one
          chain ends and the next begins. When thinking runs flank the boundary,
          omitting the block merges the runs into one contiguous span whose hashes
          cannot verify (the request is rejected), and moving it into the middle of
          a single run splits that run's chain and is likewise rejected; between
          non-thinking blocks the block's placement has no verification effect.

          - `BetaFallbackInfoParam from`

            Identifies one hop of a fallback transition.

            - `Model model`

              The model that will complete your prompt.

              See [models](https://docs.anthropic.com/en/docs/models-overview) for additional details and options.

              - `CLAUDE_FABLE_5("claude-fable-5")`

                Next generation of intelligence for the hardest knowledge work and coding problems

              - `CLAUDE_MYTHOS_5("claude-mythos-5")`

                Most capable model for cybersecurity and biology research

              - `CLAUDE_OPUS_4_8("claude-opus-4-8")`

                Frontier intelligence for long-running agents and coding

              - `CLAUDE_OPUS_4_7("claude-opus-4-7")`

                Frontier intelligence for long-running agents and coding

              - `CLAUDE_MYTHOS_PREVIEW("claude-mythos-preview")`

                New class of intelligence, strongest in coding and cybersecurity

              - `CLAUDE_OPUS_4_6("claude-opus-4-6")`

                Frontier intelligence for long-running agents and coding

              - `CLAUDE_SONNET_4_6("claude-sonnet-4-6")`

                Best combination of speed and intelligence

              - `CLAUDE_HAIKU_4_5("claude-haiku-4-5")`

                Fastest model with near-frontier intelligence

              - `CLAUDE_HAIKU_4_5_20251001("claude-haiku-4-5-20251001")`

                Fastest model with near-frontier intelligence

              - `CLAUDE_OPUS_4_5("claude-opus-4-5")`

                Premium model combining maximum intelligence with practical performance

              - `CLAUDE_OPUS_4_5_20251101("claude-opus-4-5-20251101")`

                Premium model combining maximum intelligence with practical performance

              - `CLAUDE_SONNET_4_5("claude-sonnet-4-5")`

                High-performance model for agents and coding

              - `CLAUDE_SONNET_4_5_20250929("claude-sonnet-4-5-20250929")`

                High-performance model for agents and coding

              - `CLAUDE_OPUS_4_1("claude-opus-4-1")`

                Exceptional model for specialized complex tasks

              - `CLAUDE_OPUS_4_1_20250805("claude-opus-4-1-20250805")`

                Exceptional model for specialized complex tasks

              - `CLAUDE_OPUS_4_0("claude-opus-4-0")`

                Powerful model for complex tasks

              - `CLAUDE_OPUS_4_20250514("claude-opus-4-20250514")`

                Powerful model for complex tasks

              - `CLAUDE_SONNET_4_0("claude-sonnet-4-0")`

                High-performance model with extended thinking

              - `CLAUDE_SONNET_4_20250514("claude-sonnet-4-20250514")`

                High-performance model with extended thinking

              - `CLAUDE_3_HAIKU_20240307("claude-3-haiku-20240307")`

                Fast and cost-effective model

          - `BetaFallbackInfoParam to`

            Identifies one hop of a fallback transition.

          - `JsonValue; type "fallback"constant`

            - `FALLBACK("fallback")`

    - `Role role`

      - `USER("user")`

      - `ASSISTANT("assistant")`

      - `SYSTEM("system")`

  - `Model model`

    The model that will complete your prompt.

    See [models](https://docs.anthropic.com/en/docs/models-overview) for additional details and options.

  - `Optional<BetaCacheControlEphemeral> cacheControl`

    Top-level cache control automatically applies a cache_control marker to the last cacheable block in the request.

  - `Optional<Container> container`

    Container identifier for reuse across requests.

    - `class BetaContainerParams:`

      Container parameters with skills to be loaded.

      - `Optional<String> id`

        Container id

      - `Optional<List<BetaSkillParams>> skills`

        List of skills to load in the container

        - `String skillId`

          Skill ID

        - `Type type`

          Type of skill - either 'anthropic' (built-in) or 'custom' (user-defined)

          - `ANTHROPIC("anthropic")`

          - `CUSTOM("custom")`

        - `Optional<String> version`

          Skill version or 'latest' for most recent version

    - `String`

  - `Optional<BetaContextManagementConfig> contextManagement`

    Context management configuration.

    This allows you to control how Claude manages context across multiple requests, such as whether to clear function results or not.

  - `Optional<BetaDiagnosticsParam> diagnostics`

    Request-level diagnostics. Currently carries the previous response
    id for prompt-cache divergence reporting.

  - `Optional<String> fallbackCreditToken`

    The `fallback_credit_token` from a prior refusal's `stop_details`.

    When a preceding request was refused and returned a `fallback_credit_token`,
    pass that code here on the retry to have the retry's cache-creation tokens
    for the prefix that was warm on the refused model billed at the cache-read
    rate. Must be redeemed by the same organization and workspace, with the same
    request body (optionally extended by one appended `assistant` message whose
    content is the partial text — with any trailing whitespace stripped from
    the final text block — and paired server-tool blocks streamed before the
    refusal; the appended-assistant form is not available for requests with
    `output_format` set or forced `tool_choice`), on an eligible fallback
    model, on the same platform,
    and within 5 minutes of the refusal; a mismatch is a 400. A token minted
    mid-server-tool-loop whose partial content was continuable may only be
    redeemed with the appended-assistant form — if an exact-body retry is
    rejected with a 400 saying the token must be redeemed by continuing the
    partial response, retry with the appended-assistant form instead.

    When the appended-assistant form is used on a model that otherwise disallows
    assistant-turn prefill, this token also authorizes that one prefill.

  - `Optional<List<BetaFallbackParam>> fallbacks`

    Opt-in server-side retry on one or more substitute models when the requested model declines for policy reasons. Tried in order: if the first entry also declines, the second is tried, and so on.

    - `Model model`

      The model that will complete your prompt.

      See [models](https://docs.anthropic.com/en/docs/models-overview) for additional details and options.

    - `Optional<Long> maxTokens`

    - `Optional<BetaOutputConfig> outputConfig`

      - `Optional<Effort> effort`

        All possible effort levels.

        - `LOW("low")`

        - `MEDIUM("medium")`

        - `HIGH("high")`

        - `XHIGH("xhigh")`

        - `MAX("max")`

      - `Optional<BetaJsonOutputFormat> format`

        A schema to specify Claude's output format in responses. See [structured outputs](https://platform.claude.com/docs/en/build-with-claude/structured-outputs)

        - `Schema schema`

          The JSON schema of the format

        - `JsonValue; type "json_schema"constant`

          - `JSON_SCHEMA("json_schema")`

      - `Optional<BetaTokenTaskBudget> taskBudget`

        User-configurable total token budget across contexts.

        - `long total`

          Total token budget across all contexts in the session.

        - `JsonValue; type "tokens"constant`

          The budget type. Currently only 'tokens' is supported.

          - `TOKENS("tokens")`

        - `Optional<Long> remaining`

          Remaining tokens in the budget. Use this to track usage across contexts when implementing compaction client-side. Defaults to total if not provided.

    - `Optional<Speed> speed`

      - `STANDARD("standard")`

      - `FAST("fast")`

    - `Optional<Thinking> thinking`

      - `class BetaThinkingConfigEnabled:`

        - `long budgetTokens`

          Determines how many tokens Claude can use for its internal reasoning process. Larger budgets can enable more thorough analysis for complex problems, improving response quality.

          Must be ≥1024 and less than `max_tokens`.

          See [extended thinking](https://docs.claude.com/en/docs/build-with-claude/extended-thinking) for details.

        - `JsonValue; type "enabled"constant`

          - `ENABLED("enabled")`

        - `Optional<Display> display`

          Controls how thinking content appears in the response. When set to `summarized`, thinking is returned normally. When set to `omitted`, thinking content is redacted but a signature is returned for multi-turn continuity. Defaults to `summarized`.

          - `SUMMARIZED("summarized")`

          - `OMITTED("omitted")`

      - `class BetaThinkingConfigDisabled:`

        - `JsonValue; type "disabled"constant`

          - `DISABLED("disabled")`

      - `class BetaThinkingConfigAdaptive:`

        - `JsonValue; type "adaptive"constant`

          - `ADAPTIVE("adaptive")`

        - `Optional<Display> display`

          Controls how thinking content appears in the response. When set to `summarized`, thinking is returned normally. When set to `omitted`, thinking content is redacted but a signature is returned for multi-turn continuity. Defaults to `summarized`.

          - `SUMMARIZED("summarized")`

          - `OMITTED("omitted")`

  - `Optional<String> inferenceGeo`

    Specifies the geographic region for inference processing. If not specified, the workspace's `default_inference_geo` is used.

  - `Optional<List<BetaRequestMcpServerUrlDefinition>> mcpServers`

    MCP servers to be utilized in this request

    - `String name`

    - `JsonValue; type "url"constant`

      - `URL("url")`

    - `String url`

    - `Optional<String> authorizationToken`

    - `Optional<BetaRequestMcpServerToolConfiguration> toolConfiguration`

      - `Optional<List<String>> allowedTools`

      - `Optional<Boolean> enabled`

  - `Optional<BetaMetadata> metadata`

    An object describing metadata about the request.

  - `Optional<BetaOutputConfig> outputConfig`

    Configuration options for the model's output, such as the output format.

  - `Optional<BetaJsonOutputFormat> outputFormat`

    Deprecated: Use `output_config.format` instead. See [structured outputs](https://platform.claude.com/docs/en/build-with-claude/structured-outputs)

    A schema to specify Claude's output format in responses. This parameter will be removed in a future release.

  - `Optional<ServiceTier> serviceTier`

    Determines whether to use priority capacity (if available) or standard capacity for this request.

    Anthropic offers different levels of service for your API requests. See [service-tiers](https://docs.claude.com/en/api/service-tiers) for details.

    - `AUTO("auto")`

    - `STANDARD_ONLY("standard_only")`

  - `Optional<Speed> speed`

    The inference speed mode for this request. `"fast"` enables high output-tokens-per-second inference.

    - `STANDARD("standard")`

    - `FAST("fast")`

  - `Optional<List<String>> stopSequences`

    Custom text sequences that will cause the model to stop generating.

    Our models will normally stop when they have naturally completed their turn, which will result in a response `stop_reason` of `"end_turn"`.

    If you want the model to stop generating when it encounters custom strings of text, you can use the `stop_sequences` parameter. If the model encounters one of the custom sequences, the response `stop_reason` value will be `"stop_sequence"` and the response `stop_sequence` value will contain the matched stop sequence.

  - `Optional<System> system`

    System prompt.

    A system prompt is a way of providing context and instructions to Claude, such as specifying a particular goal or role. See our [guide to system prompts](https://docs.claude.com/en/docs/system-prompts).

    - `String`

    - `List<BetaTextBlockParam>`

      - `String text`

      - `JsonValue; type "text"constant`

      - `Optional<BetaCacheControlEphemeral> cacheControl`

        Create a cache control breakpoint at this content block.

      - `Optional<List<BetaTextCitationParam>> citations`

  - `Optional<Double> temperature`

    Amount of randomness injected into the response.

    Defaults to `1.0`. Ranges from `0.0` to `1.0`. Use `temperature` closer to `0.0` for analytical / multiple choice, and closer to `1.0` for creative and generative tasks.

    Note that even with `temperature` of `0.0`, the results will not be fully deterministic.

  - `Optional<BetaThinkingConfigParam> thinking`

    Configuration for enabling Claude's extended thinking.

    When enabled, responses include `thinking` content blocks showing Claude's thinking process before the final answer. Requires a minimum budget of 1,024 tokens and counts towards your `max_tokens` limit.

    See [extended thinking](https://docs.claude.com/en/docs/build-with-claude/extended-thinking) for details.

  - `Optional<BetaToolChoice> toolChoice`

    How the model should use the provided tools. The model can use a specific tool, any available tool, decide by itself, or not use tools at all.

  - `Optional<List<BetaToolUnion>> tools`

    Definitions of tools that the model may use.

    If you include `tools` in your API request, the model may return `tool_use` content blocks that represent the model's use of those tools. You can then run those tools using the tool input generated by the model and then optionally return results back to the model using `tool_result` content blocks.

    There are two types of tools: **client tools** and **server tools**. The behavior described below applies to client tools. For [server tools](https://docs.claude.com/en/docs/agents-and-tools/tool-use/overview#server-tools), see their individual documentation as each has its own behavior (e.g., the [web search tool](https://docs.claude.com/en/docs/agents-and-tools/tool-use/web-search-tool)).

    Each tool definition includes:

    * `name`: Name of the tool.
    * `description`: Optional, but strongly-recommended description of the tool.
    * `input_schema`: [JSON schema](https://json-schema.org/draft/2020-12) for the tool `input` shape that the model will produce in `tool_use` output content blocks.

    For example, if you defined `tools` as:

    ```json
    [
      {
        "name": "get_stock_price",
        "description": "Get the current stock price for a given ticker symbol.",
        "input_schema": {
          "type": "object",
          "properties": {
            "ticker": {
              "type": "string",
              "description": "The stock ticker symbol, e.g. AAPL for Apple Inc."
            }
          },
          "required": ["ticker"]
        }
      }
    ]
    ```

    And then asked the model "What's the S&P 500 at today?", the model might produce `tool_use` content blocks in the response like this:

    ```json
    [
      {
        "type": "tool_use",
        "id": "toolu_01D7FLrfh4GYq7yT1ULFeyMV",
        "name": "get_stock_price",
        "input": { "ticker": "^GSPC" }
      }
    ]
    ```

    You might then run your `get_stock_price` tool with `{"ticker": "^GSPC"}` as an input, and return the following back to the model in a subsequent `user` message:

    ```json
    [
      {
        "type": "tool_result",
        "tool_use_id": "toolu_01D7FLrfh4GYq7yT1ULFeyMV",
        "content": "259.75 USD"
      }
    ]
    ```

    Tools can be used for workflows that include running client-side tools and functions, or more generally whenever you want the model to produce a particular JSON structure of output.

    See our [guide](https://docs.claude.com/en/docs/tool-use) for more details.

    - `class BetaTool:`

      - `InputSchema inputSchema`

        [JSON schema](https://json-schema.org/draft/2020-12) for this tool's input.

        This defines the shape of the `input` that your tool accepts and that the model will produce.

        - `JsonValue; type "object"constant`

          - `OBJECT("object")`

        - `Optional<Properties> properties`

        - `Optional<List<String>> required`

      - `String name`

        Name of the tool.

        This is how the tool will be called by the model and in `tool_use` blocks.

      - `Optional<List<AllowedCaller>> allowedCallers`

        - `DIRECT("direct")`

        - `CODE_EXECUTION_20250825("code_execution_20250825")`

        - `CODE_EXECUTION_20260120("code_execution_20260120")`

      - `Optional<BetaCacheControlEphemeral> cacheControl`

        Create a cache control breakpoint at this content block.

      - `Optional<Boolean> deferLoading`

        If true, tool will not be included in initial system prompt. Only loaded when returned via tool_reference from tool search.

      - `Optional<String> description`

        Description of what this tool does.

        Tool descriptions should be as detailed as possible. The more information that the model has about what the tool is and how to use it, the better it will perform. You can use natural language descriptions to reinforce important aspects of the tool input JSON schema.

      - `Optional<Boolean> eagerInputStreaming`

        Enable eager input streaming for this tool. When true, tool input parameters will be streamed incrementally as they are generated, and types will be inferred on-the-fly rather than buffering the full JSON output. When false, streaming is disabled for this tool even if the fine-grained-tool-streaming beta is active. When null (default), uses the default behavior based on beta headers.

      - `Optional<List<InputExample>> inputExamples`

      - `Optional<Boolean> strict`

        When true, guarantees schema validation on tool names and inputs

      - `Optional<Type> type`

        - `CUSTOM("custom")`

    - `class BetaToolBash20241022:`

      - `JsonValue; name "bash"constant`

        Name of the tool.

        This is how the tool will be called by the model and in `tool_use` blocks.

        - `BASH("bash")`

      - `JsonValue; type "bash_20241022"constant`

        - `BASH_20241022("bash_20241022")`

      - `Optional<List<AllowedCaller>> allowedCallers`

        - `DIRECT("direct")`

        - `CODE_EXECUTION_20250825("code_execution_20250825")`

        - `CODE_EXECUTION_20260120("code_execution_20260120")`

      - `Optional<BetaCacheControlEphemeral> cacheControl`

        Create a cache control breakpoint at this content block.

      - `Optional<Boolean> deferLoading`

        If true, tool will not be included in initial system prompt. Only loaded when returned via tool_reference from tool search.

      - `Optional<List<InputExample>> inputExamples`

      - `Optional<Boolean> strict`

        When true, guarantees schema validation on tool names and inputs

    - `class BetaToolBash20250124:`

      - `JsonValue; name "bash"constant`

        Name of the tool.

        This is how the tool will be called by the model and in `tool_use` blocks.

        - `BASH("bash")`

      - `JsonValue; type "bash_20250124"constant`

        - `BASH_20250124("bash_20250124")`

      - `Optional<List<AllowedCaller>> allowedCallers`

        - `DIRECT("direct")`

        - `CODE_EXECUTION_20250825("code_execution_20250825")`

        - `CODE_EXECUTION_20260120("code_execution_20260120")`

      - `Optional<BetaCacheControlEphemeral> cacheControl`

        Create a cache control breakpoint at this content block.

      - `Optional<Boolean> deferLoading`

        If true, tool will not be included in initial system prompt. Only loaded when returned via tool_reference from tool search.

      - `Optional<List<InputExample>> inputExamples`

      - `Optional<Boolean> strict`

        When true, guarantees schema validation on tool names and inputs

    - `class BetaCodeExecutionTool20250522:`

      - `JsonValue; name "code_execution"constant`

        Name of the tool.

        This is how the tool will be called by the model and in `tool_use` blocks.

        - `CODE_EXECUTION("code_execution")`

      - `JsonValue; type "code_execution_20250522"constant`

        - `CODE_EXECUTION_20250522("code_execution_20250522")`

      - `Optional<List<AllowedCaller>> allowedCallers`

        - `DIRECT("direct")`

        - `CODE_EXECUTION_20250825("code_execution_20250825")`

        - `CODE_EXECUTION_20260120("code_execution_20260120")`

      - `Optional<BetaCacheControlEphemeral> cacheControl`

        Create a cache control breakpoint at this content block.

      - `Optional<Boolean> deferLoading`

        If true, tool will not be included in initial system prompt. Only loaded when returned via tool_reference from tool search.

      - `Optional<Boolean> strict`

        When true, guarantees schema validation on tool names and inputs

    - `class BetaCodeExecutionTool20250825:`

      - `JsonValue; name "code_execution"constant`

        Name of the tool.

        This is how the tool will be called by the model and in `tool_use` blocks.

        - `CODE_EXECUTION("code_execution")`

      - `JsonValue; type "code_execution_20250825"constant`

        - `CODE_EXECUTION_20250825("code_execution_20250825")`

      - `Optional<List<AllowedCaller>> allowedCallers`

        - `DIRECT("direct")`

        - `CODE_EXECUTION_20250825("code_execution_20250825")`

        - `CODE_EXECUTION_20260120("code_execution_20260120")`

      - `Optional<BetaCacheControlEphemeral> cacheControl`

        Create a cache control breakpoint at this content block.

      - `Optional<Boolean> deferLoading`

        If true, tool will not be included in initial system prompt. Only loaded when returned via tool_reference from tool search.

      - `Optional<Boolean> strict`

        When true, guarantees schema validation on tool names and inputs

    - `class BetaCodeExecutionTool20260120:`

      Code execution tool with REPL state persistence (daemon mode + gVisor checkpoint).

      - `JsonValue; name "code_execution"constant`

        Name of the tool.

        This is how the tool will be called by the model and in `tool_use` blocks.

        - `CODE_EXECUTION("code_execution")`

      - `JsonValue; type "code_execution_20260120"constant`

        - `CODE_EXECUTION_20260120("code_execution_20260120")`

      - `Optional<List<AllowedCaller>> allowedCallers`

        - `DIRECT("direct")`

        - `CODE_EXECUTION_20250825("code_execution_20250825")`

        - `CODE_EXECUTION_20260120("code_execution_20260120")`

      - `Optional<BetaCacheControlEphemeral> cacheControl`

        Create a cache control breakpoint at this content block.

      - `Optional<Boolean> deferLoading`

        If true, tool will not be included in initial system prompt. Only loaded when returned via tool_reference from tool search.

      - `Optional<Boolean> strict`

        When true, guarantees schema validation on tool names and inputs

    - `class BetaToolComputerUse20241022:`

      - `long displayHeightPx`

        The height of the display in pixels.

      - `long displayWidthPx`

        The width of the display in pixels.

      - `JsonValue; name "computer"constant`

        Name of the tool.

        This is how the tool will be called by the model and in `tool_use` blocks.

        - `COMPUTER("computer")`

      - `JsonValue; type "computer_20241022"constant`

        - `COMPUTER_20241022("computer_20241022")`

      - `Optional<List<AllowedCaller>> allowedCallers`

        - `DIRECT("direct")`

        - `CODE_EXECUTION_20250825("code_execution_20250825")`

        - `CODE_EXECUTION_20260120("code_execution_20260120")`

      - `Optional<BetaCacheControlEphemeral> cacheControl`

        Create a cache control breakpoint at this content block.

      - `Optional<Boolean> deferLoading`

        If true, tool will not be included in initial system prompt. Only loaded when returned via tool_reference from tool search.

      - `Optional<Long> displayNumber`

        The X11 display number (e.g. 0, 1) for the display.

      - `Optional<List<InputExample>> inputExamples`

      - `Optional<Boolean> strict`

        When true, guarantees schema validation on tool names and inputs

    - `class BetaMemoryTool20250818:`

      - `JsonValue; name "memory"constant`

        Name of the tool.

        This is how the tool will be called by the model and in `tool_use` blocks.

        - `MEMORY("memory")`

      - `JsonValue; type "memory_20250818"constant`

        - `MEMORY_20250818("memory_20250818")`

      - `Optional<List<AllowedCaller>> allowedCallers`

        - `DIRECT("direct")`

        - `CODE_EXECUTION_20250825("code_execution_20250825")`

        - `CODE_EXECUTION_20260120("code_execution_20260120")`

      - `Optional<BetaCacheControlEphemeral> cacheControl`

        Create a cache control breakpoint at this content block.

      - `Optional<Boolean> deferLoading`

        If true, tool will not be included in initial system prompt. Only loaded when returned via tool_reference from tool search.

      - `Optional<List<InputExample>> inputExamples`

      - `Optional<Boolean> strict`

        When true, guarantees schema validation on tool names and inputs

    - `class BetaToolComputerUse20250124:`

      - `long displayHeightPx`

        The height of the display in pixels.

      - `long displayWidthPx`

        The width of the display in pixels.

      - `JsonValue; name "computer"constant`

        Name of the tool.

        This is how the tool will be called by the model and in `tool_use` blocks.

        - `COMPUTER("computer")`

      - `JsonValue; type "computer_20250124"constant`

        - `COMPUTER_20250124("computer_20250124")`

      - `Optional<List<AllowedCaller>> allowedCallers`

        - `DIRECT("direct")`

        - `CODE_EXECUTION_20250825("code_execution_20250825")`

        - `CODE_EXECUTION_20260120("code_execution_20260120")`

      - `Optional<BetaCacheControlEphemeral> cacheControl`

        Create a cache control breakpoint at this content block.

      - `Optional<Boolean> deferLoading`

        If true, tool will not be included in initial system prompt. Only loaded when returned via tool_reference from tool search.

      - `Optional<Long> displayNumber`

        The X11 display number (e.g. 0, 1) for the display.

      - `Optional<List<InputExample>> inputExamples`

      - `Optional<Boolean> strict`

        When true, guarantees schema validation on tool names and inputs

    - `class BetaToolTextEditor20241022:`

      - `JsonValue; name "str_replace_editor"constant`

        Name of the tool.

        This is how the tool will be called by the model and in `tool_use` blocks.

        - `STR_REPLACE_EDITOR("str_replace_editor")`

      - `JsonValue; type "text_editor_20241022"constant`

        - `TEXT_EDITOR_20241022("text_editor_20241022")`

      - `Optional<List<AllowedCaller>> allowedCallers`

        - `DIRECT("direct")`

        - `CODE_EXECUTION_20250825("code_execution_20250825")`

        - `CODE_EXECUTION_20260120("code_execution_20260120")`

      - `Optional<BetaCacheControlEphemeral> cacheControl`

        Create a cache control breakpoint at this content block.

      - `Optional<Boolean> deferLoading`

        If true, tool will not be included in initial system prompt. Only loaded when returned via tool_reference from tool search.

      - `Optional<List<InputExample>> inputExamples`

      - `Optional<Boolean> strict`

        When true, guarantees schema validation on tool names and inputs

    - `class BetaToolComputerUse20251124:`

      - `long displayHeightPx`

        The height of the display in pixels.

      - `long displayWidthPx`

        The width of the display in pixels.

      - `JsonValue; name "computer"constant`

        Name of the tool.

        This is how the tool will be called by the model and in `tool_use` blocks.

        - `COMPUTER("computer")`

      - `JsonValue; type "computer_20251124"constant`

        - `COMPUTER_20251124("computer_20251124")`

      - `Optional<List<AllowedCaller>> allowedCallers`

        - `DIRECT("direct")`

        - `CODE_EXECUTION_20250825("code_execution_20250825")`

        - `CODE_EXECUTION_20260120("code_execution_20260120")`

      - `Optional<BetaCacheControlEphemeral> cacheControl`

        Create a cache control breakpoint at this content block.

      - `Optional<Boolean> deferLoading`

        If true, tool will not be included in initial system prompt. Only loaded when returned via tool_reference from tool search.

      - `Optional<Long> displayNumber`

        The X11 display number (e.g. 0, 1) for the display.

      - `Optional<Boolean> enableZoom`

        Whether to enable an action to take a zoomed-in screenshot of the screen.

      - `Optional<List<InputExample>> inputExamples`

      - `Optional<Boolean> strict`

        When true, guarantees schema validation on tool names and inputs

    - `class BetaToolTextEditor20250124:`

      - `JsonValue; name "str_replace_editor"constant`

        Name of the tool.

        This is how the tool will be called by the model and in `tool_use` blocks.

        - `STR_REPLACE_EDITOR("str_replace_editor")`

      - `JsonValue; type "text_editor_20250124"constant`

        - `TEXT_EDITOR_20250124("text_editor_20250124")`

      - `Optional<List<AllowedCaller>> allowedCallers`

        - `DIRECT("direct")`

        - `CODE_EXECUTION_20250825("code_execution_20250825")`

        - `CODE_EXECUTION_20260120("code_execution_20260120")`

      - `Optional<BetaCacheControlEphemeral> cacheControl`

        Create a cache control breakpoint at this content block.

      - `Optional<Boolean> deferLoading`

        If true, tool will not be included in initial system prompt. Only loaded when returned via tool_reference from tool search.

      - `Optional<List<InputExample>> inputExamples`

      - `Optional<Boolean> strict`

        When true, guarantees schema validation on tool names and inputs

    - `class BetaToolTextEditor20250429:`

      - `JsonValue; name "str_replace_based_edit_tool"constant`

        Name of the tool.

        This is how the tool will be called by the model and in `tool_use` blocks.

        - `STR_REPLACE_BASED_EDIT_TOOL("str_replace_based_edit_tool")`

      - `JsonValue; type "text_editor_20250429"constant`

        - `TEXT_EDITOR_20250429("text_editor_20250429")`

      - `Optional<List<AllowedCaller>> allowedCallers`

        - `DIRECT("direct")`

        - `CODE_EXECUTION_20250825("code_execution_20250825")`

        - `CODE_EXECUTION_20260120("code_execution_20260120")`

      - `Optional<BetaCacheControlEphemeral> cacheControl`

        Create a cache control breakpoint at this content block.

      - `Optional<Boolean> deferLoading`

        If true, tool will not be included in initial system prompt. Only loaded when returned via tool_reference from tool search.

      - `Optional<List<InputExample>> inputExamples`

      - `Optional<Boolean> strict`

        When true, guarantees schema validation on tool names and inputs

    - `class BetaToolTextEditor20250728:`

      - `JsonValue; name "str_replace_based_edit_tool"constant`

        Name of the tool.

        This is how the tool will be called by the model and in `tool_use` blocks.

        - `STR_REPLACE_BASED_EDIT_TOOL("str_replace_based_edit_tool")`

      - `JsonValue; type "text_editor_20250728"constant`

        - `TEXT_EDITOR_20250728("text_editor_20250728")`

      - `Optional<List<AllowedCaller>> allowedCallers`

        - `DIRECT("direct")`

        - `CODE_EXECUTION_20250825("code_execution_20250825")`

        - `CODE_EXECUTION_20260120("code_execution_20260120")`

      - `Optional<BetaCacheControlEphemeral> cacheControl`

        Create a cache control breakpoint at this content block.

      - `Optional<Boolean> deferLoading`

        If true, tool will not be included in initial system prompt. Only loaded when returned via tool_reference from tool search.

      - `Optional<List<InputExample>> inputExamples`

      - `Optional<Long> maxCharacters`

        Maximum number of characters to display when viewing a file. If not specified, defaults to displaying the full file.

      - `Optional<Boolean> strict`

        When true, guarantees schema validation on tool names and inputs

    - `class BetaWebSearchTool20250305:`

      - `JsonValue; name "web_search"constant`

        Name of the tool.

        This is how the tool will be called by the model and in `tool_use` blocks.

        - `WEB_SEARCH("web_search")`

      - `JsonValue; type "web_search_20250305"constant`

        - `WEB_SEARCH_20250305("web_search_20250305")`

      - `Optional<List<AllowedCaller>> allowedCallers`

        - `DIRECT("direct")`

        - `CODE_EXECUTION_20250825("code_execution_20250825")`

        - `CODE_EXECUTION_20260120("code_execution_20260120")`

      - `Optional<List<String>> allowedDomains`

        If provided, only these domains will be included in results. Cannot be used alongside `blocked_domains`.

      - `Optional<List<String>> blockedDomains`

        If provided, these domains will never appear in results. Cannot be used alongside `allowed_domains`.

      - `Optional<BetaCacheControlEphemeral> cacheControl`

        Create a cache control breakpoint at this content block.

      - `Optional<Boolean> deferLoading`

        If true, tool will not be included in initial system prompt. Only loaded when returned via tool_reference from tool search.

      - `Optional<Long> maxUses`

        Maximum number of times the tool can be used in the API request.

      - `Optional<Boolean> strict`

        When true, guarantees schema validation on tool names and inputs

      - `Optional<BetaUserLocation> userLocation`

        Parameters for the user's location. Used to provide more relevant search results.

        - `JsonValue; type "approximate"constant`

          - `APPROXIMATE("approximate")`

        - `Optional<String> city`

          The city of the user.

        - `Optional<String> country`

          The two letter [ISO country code](https://en.wikipedia.org/wiki/ISO_3166-1_alpha-2) of the user.

        - `Optional<String> region`

          The region of the user.

        - `Optional<String> timezone`

          The [IANA timezone](https://nodatime.org/TimeZones) of the user.

    - `class BetaWebFetchTool20250910:`

      - `JsonValue; name "web_fetch"constant`

        Name of the tool.

        This is how the tool will be called by the model and in `tool_use` blocks.

        - `WEB_FETCH("web_fetch")`

      - `JsonValue; type "web_fetch_20250910"constant`

        - `WEB_FETCH_20250910("web_fetch_20250910")`

      - `Optional<List<AllowedCaller>> allowedCallers`

        - `DIRECT("direct")`

        - `CODE_EXECUTION_20250825("code_execution_20250825")`

        - `CODE_EXECUTION_20260120("code_execution_20260120")`

      - `Optional<List<String>> allowedDomains`

        List of domains to allow fetching from

      - `Optional<List<String>> blockedDomains`

        List of domains to block fetching from

      - `Optional<BetaCacheControlEphemeral> cacheControl`

        Create a cache control breakpoint at this content block.

      - `Optional<BetaCitationsConfigParam> citations`

        Citations configuration for fetched documents. Citations are disabled by default.

      - `Optional<Boolean> deferLoading`

        If true, tool will not be included in initial system prompt. Only loaded when returned via tool_reference from tool search.

      - `Optional<Long> maxContentTokens`

        Maximum number of tokens used by including web page text content in the context. The limit is approximate and does not apply to binary content such as PDFs.

      - `Optional<Long> maxUses`

        Maximum number of times the tool can be used in the API request.

      - `Optional<Boolean> strict`

        When true, guarantees schema validation on tool names and inputs

    - `class BetaWebSearchTool20260209:`

      - `JsonValue; name "web_search"constant`

        Name of the tool.

        This is how the tool will be called by the model and in `tool_use` blocks.

        - `WEB_SEARCH("web_search")`

      - `JsonValue; type "web_search_20260209"constant`

        - `WEB_SEARCH_20260209("web_search_20260209")`

      - `Optional<List<AllowedCaller>> allowedCallers`

        - `DIRECT("direct")`

        - `CODE_EXECUTION_20250825("code_execution_20250825")`

        - `CODE_EXECUTION_20260120("code_execution_20260120")`

      - `Optional<List<String>> allowedDomains`

        If provided, only these domains will be included in results. Cannot be used alongside `blocked_domains`.

      - `Optional<List<String>> blockedDomains`

        If provided, these domains will never appear in results. Cannot be used alongside `allowed_domains`.

      - `Optional<BetaCacheControlEphemeral> cacheControl`

        Create a cache control breakpoint at this content block.

      - `Optional<Boolean> deferLoading`

        If true, tool will not be included in initial system prompt. Only loaded when returned via tool_reference from tool search.

      - `Optional<Long> maxUses`

        Maximum number of times the tool can be used in the API request.

      - `Optional<Boolean> strict`

        When true, guarantees schema validation on tool names and inputs

      - `Optional<BetaUserLocation> userLocation`

        Parameters for the user's location. Used to provide more relevant search results.

    - `class BetaWebFetchTool20260209:`

      - `JsonValue; name "web_fetch"constant`

        Name of the tool.

        This is how the tool will be called by the model and in `tool_use` blocks.

        - `WEB_FETCH("web_fetch")`

      - `JsonValue; type "web_fetch_20260209"constant`

        - `WEB_FETCH_20260209("web_fetch_20260209")`

      - `Optional<List<AllowedCaller>> allowedCallers`

        - `DIRECT("direct")`

        - `CODE_EXECUTION_20250825("code_execution_20250825")`

        - `CODE_EXECUTION_20260120("code_execution_20260120")`

      - `Optional<List<String>> allowedDomains`

        List of domains to allow fetching from

      - `Optional<List<String>> blockedDomains`

        List of domains to block fetching from

      - `Optional<BetaCacheControlEphemeral> cacheControl`

        Create a cache control breakpoint at this content block.

      - `Optional<BetaCitationsConfigParam> citations`

        Citations configuration for fetched documents. Citations are disabled by default.

      - `Optional<Boolean> deferLoading`

        If true, tool will not be included in initial system prompt. Only loaded when returned via tool_reference from tool search.

      - `Optional<Long> maxContentTokens`

        Maximum number of tokens used by including web page text content in the context. The limit is approximate and does not apply to binary content such as PDFs.

      - `Optional<Long> maxUses`

        Maximum number of times the tool can be used in the API request.

      - `Optional<Boolean> strict`

        When true, guarantees schema validation on tool names and inputs

    - `class BetaWebFetchTool20260309:`

      Web fetch tool with use_cache parameter for bypassing cached content.

      - `JsonValue; name "web_fetch"constant`

        Name of the tool.

        This is how the tool will be called by the model and in `tool_use` blocks.

        - `WEB_FETCH("web_fetch")`

      - `JsonValue; type "web_fetch_20260309"constant`

        - `WEB_FETCH_20260309("web_fetch_20260309")`

      - `Optional<List<AllowedCaller>> allowedCallers`

        - `DIRECT("direct")`

        - `CODE_EXECUTION_20250825("code_execution_20250825")`

        - `CODE_EXECUTION_20260120("code_execution_20260120")`

      - `Optional<List<String>> allowedDomains`

        List of domains to allow fetching from

      - `Optional<List<String>> blockedDomains`

        List of domains to block fetching from

      - `Optional<BetaCacheControlEphemeral> cacheControl`

        Create a cache control breakpoint at this content block.

      - `Optional<BetaCitationsConfigParam> citations`

        Citations configuration for fetched documents. Citations are disabled by default.

      - `Optional<Boolean> deferLoading`

        If true, tool will not be included in initial system prompt. Only loaded when returned via tool_reference from tool search.

      - `Optional<Long> maxContentTokens`

        Maximum number of tokens used by including web page text content in the context. The limit is approximate and does not apply to binary content such as PDFs.

      - `Optional<Long> maxUses`

        Maximum number of times the tool can be used in the API request.

      - `Optional<Boolean> strict`

        When true, guarantees schema validation on tool names and inputs

      - `Optional<Boolean> useCache`

        Whether to use cached content. Set to false to bypass the cache and fetch fresh content. Only set to false when the user explicitly requests fresh content or when fetching rapidly-changing sources.

    - `class BetaAdvisorTool20260301:`

      - `Model model`

        The model that will complete your prompt.

        See [models](https://docs.anthropic.com/en/docs/models-overview) for additional details and options.

      - `JsonValue; name "advisor"constant`

        Name of the tool.

        This is how the tool will be called by the model and in `tool_use` blocks.

        - `ADVISOR("advisor")`

      - `JsonValue; type "advisor_20260301"constant`

        - `ADVISOR_20260301("advisor_20260301")`

      - `Optional<List<AllowedCaller>> allowedCallers`

        - `DIRECT("direct")`

        - `CODE_EXECUTION_20250825("code_execution_20250825")`

        - `CODE_EXECUTION_20260120("code_execution_20260120")`

      - `Optional<BetaCacheControlEphemeral> cacheControl`

        Create a cache control breakpoint at this content block.

      - `Optional<BetaCacheControlEphemeral> caching`

        Caching for the advisor's own prompt. When set, each advisor call writes a cache entry at the given TTL so subsequent calls in the same conversation read the stable prefix. When omitted, the advisor prompt is not cached.

      - `Optional<Boolean> deferLoading`

        If true, tool will not be included in initial system prompt. Only loaded when returned via tool_reference from tool search.

      - `Optional<Long> maxTokens`

        Bounds the advisor's total output (thinking + text) per call. When the advisor hits this cap, the returned advisor_result or advisor_redacted_result block carries stop_reason='max_tokens', and a truncation note is appended to the advice text the worker model sees (inside the encrypted blob in redacted mode). When set, the server also emits a remaining-tokens budget block in the advisor's prompt so the advisor self-shapes toward the cap. When omitted, the advisor model's default output cap applies and no budget block is emitted.

      - `Optional<Long> maxUses`

        Maximum number of times the tool can be used in the API request.

      - `Optional<Boolean> strict`

        When true, guarantees schema validation on tool names and inputs

    - `class BetaToolSearchToolBm25_20251119:`

      - `JsonValue; name "tool_search_tool_bm25"constant`

        Name of the tool.

        This is how the tool will be called by the model and in `tool_use` blocks.

        - `TOOL_SEARCH_TOOL_BM25("tool_search_tool_bm25")`

      - `Type type`

        - `TOOL_SEARCH_TOOL_BM25_20251119("tool_search_tool_bm25_20251119")`

        - `TOOL_SEARCH_TOOL_BM25("tool_search_tool_bm25")`

      - `Optional<List<AllowedCaller>> allowedCallers`

        - `DIRECT("direct")`

        - `CODE_EXECUTION_20250825("code_execution_20250825")`

        - `CODE_EXECUTION_20260120("code_execution_20260120")`

      - `Optional<BetaCacheControlEphemeral> cacheControl`

        Create a cache control breakpoint at this content block.

      - `Optional<Boolean> deferLoading`

        If true, tool will not be included in initial system prompt. Only loaded when returned via tool_reference from tool search.

      - `Optional<Boolean> strict`

        When true, guarantees schema validation on tool names and inputs

    - `class BetaToolSearchToolRegex20251119:`

      - `JsonValue; name "tool_search_tool_regex"constant`

        Name of the tool.

        This is how the tool will be called by the model and in `tool_use` blocks.

        - `TOOL_SEARCH_TOOL_REGEX("tool_search_tool_regex")`

      - `Type type`

        - `TOOL_SEARCH_TOOL_REGEX_20251119("tool_search_tool_regex_20251119")`

        - `TOOL_SEARCH_TOOL_REGEX("tool_search_tool_regex")`

      - `Optional<List<AllowedCaller>> allowedCallers`

        - `DIRECT("direct")`

        - `CODE_EXECUTION_20250825("code_execution_20250825")`

        - `CODE_EXECUTION_20260120("code_execution_20260120")`

      - `Optional<BetaCacheControlEphemeral> cacheControl`

        Create a cache control breakpoint at this content block.

      - `Optional<Boolean> deferLoading`

        If true, tool will not be included in initial system prompt. Only loaded when returned via tool_reference from tool search.

      - `Optional<Boolean> strict`

        When true, guarantees schema validation on tool names and inputs

    - `class BetaMcpToolset:`

      Configuration for a group of tools from an MCP server.

      Allows configuring enabled status and defer_loading for all tools
      from an MCP server, with optional per-tool overrides.

      - `String mcpServerName`

        Name of the MCP server to configure tools for

      - `JsonValue; type "mcp_toolset"constant`

        - `MCP_TOOLSET("mcp_toolset")`

      - `Optional<BetaCacheControlEphemeral> cacheControl`

        Create a cache control breakpoint at this content block.

      - `Optional<Configs> configs`

        Configuration overrides for specific tools, keyed by tool name

        - `Optional<Boolean> deferLoading`

        - `Optional<Boolean> enabled`

      - `Optional<BetaMcpToolDefaultConfig> defaultConfig`

        Default configuration applied to all tools from this server

        - `Optional<Boolean> deferLoading`

        - `Optional<Boolean> enabled`

  - `Optional<Long> topK`

    Only sample from the top K options for each subsequent token.

    Used to remove "long tail" low probability responses. [Learn more technical details here](https://towardsdatascience.com/how-to-sample-from-language-models-682bceb97277).

    Recommended for advanced use cases only.

  - `Optional<Double> topP`

    Use nucleus sampling.

    In nucleus sampling, we compute the cumulative distribution over all the options for each subsequent token in decreasing probability order and cut it off once it reaches a particular probability specified by `top_p`.

    Recommended for advanced use cases only.

  - `Optional<String> userProfileId`

    The user profile ID to attribute this request to. Use when acting on behalf of a party other than your organization.

### Returns

- `class BetaMessage:`

  - `String id`

    Unique object identifier.

    The format and length of IDs may change over time.

  - `Optional<BetaContainer> container`

    Information about the container used in the request (for the code execution tool)

    - `String id`

      Identifier for the container used in this request

    - `LocalDateTime expiresAt`

      The time at which the container will expire.

    - `Optional<List<BetaSkill>> skills`

      Skills loaded in the container

      - `String skillId`

        Skill ID

      - `Type type`

        Type of skill - either 'anthropic' (built-in) or 'custom' (user-defined)

        - `ANTHROPIC("anthropic")`

        - `CUSTOM("custom")`

      - `String version`

        Skill version or 'latest' for most recent version

  - `List<BetaContentBlock> content`

    Content generated by the model.

    This is an array of content blocks, each of which has a `type` that determines its shape.

    Example:

    ```json
    [{"type": "text", "text": "Hi, I'm Claude."}]
    ```

    If the request input `messages` ended with an `assistant` turn, then the response `content` will continue directly from that last turn. You can use this to constrain the model's output.

    For example, if the input `messages` were:

    ```json
    [
      {"role": "user", "content": "What's the Greek name for Sun? (A) Sol (B) Helios (C) Sun"},
      {"role": "assistant", "content": "The best answer is ("}
    ]
    ```

    Then the response `content` might be:

    ```json
    [{"type": "text", "text": "B)"}]
    ```

    - `class BetaTextBlock:`

      - `Optional<List<BetaTextCitation>> citations`

        Citations supporting the text block.

        The type of citation returned will depend on the type of document being cited. Citing a PDF results in `page_location`, plain text results in `char_location`, and content document results in `content_block_location`.

        - `class BetaCitationCharLocation:`

          - `String citedText`

          - `long documentIndex`

          - `Optional<String> documentTitle`

          - `long endCharIndex`

          - `Optional<String> fileId`

          - `long startCharIndex`

          - `JsonValue; type "char_location"constant`

            - `CHAR_LOCATION("char_location")`

        - `class BetaCitationPageLocation:`

          - `String citedText`

          - `long documentIndex`

          - `Optional<String> documentTitle`

          - `long endPageNumber`

          - `Optional<String> fileId`

          - `long startPageNumber`

          - `JsonValue; type "page_location"constant`

            - `PAGE_LOCATION("page_location")`

        - `class BetaCitationContentBlockLocation:`

          - `String citedText`

            The full text of the cited block range, concatenated.

            Always equals the contents of `content[start_block_index:end_block_index]` joined together. The text block is the minimal citable unit; this field is never a substring of a single block. Not counted toward output tokens, and not counted toward input tokens when sent back in subsequent turns.

          - `long documentIndex`

          - `Optional<String> documentTitle`

          - `long endBlockIndex`

            Exclusive 0-based end index of the cited block range in the source's `content` array.

            Always greater than `start_block_index`; a single-block citation has `end_block_index = start_block_index + 1`.

          - `Optional<String> fileId`

          - `long startBlockIndex`

            0-based index of the first cited block in the source's `content` array.

          - `JsonValue; type "content_block_location"constant`

            - `CONTENT_BLOCK_LOCATION("content_block_location")`

        - `class BetaCitationsWebSearchResultLocation:`

          - `String citedText`

          - `String encryptedIndex`

          - `Optional<String> title`

          - `JsonValue; type "web_search_result_location"constant`

            - `WEB_SEARCH_RESULT_LOCATION("web_search_result_location")`

          - `String url`

        - `class BetaCitationSearchResultLocation:`

          - `String citedText`

            The full text of the cited block range, concatenated.

            Always equals the contents of `content[start_block_index:end_block_index]` joined together. The text block is the minimal citable unit; this field is never a substring of a single block. Not counted toward output tokens, and not counted toward input tokens when sent back in subsequent turns.

          - `long endBlockIndex`

            Exclusive 0-based end index of the cited block range in the source's `content` array.

            Always greater than `start_block_index`; a single-block citation has `end_block_index = start_block_index + 1`.

          - `long searchResultIndex`

            0-based index of the cited search result among all `search_result` content blocks in the request, in the order they appear across messages and tool results.

            Counted separately from `document_index`; server-side web search results are not included in this count.

          - `String source`

          - `long startBlockIndex`

            0-based index of the first cited block in the source's `content` array.

          - `Optional<String> title`

          - `JsonValue; type "search_result_location"constant`

            - `SEARCH_RESULT_LOCATION("search_result_location")`

      - `String text`

      - `JsonValue; type "text"constant`

        - `TEXT("text")`

    - `class BetaThinkingBlock:`

      - `String signature`

      - `String thinking`

      - `JsonValue; type "thinking"constant`

        - `THINKING("thinking")`

    - `class BetaRedactedThinkingBlock:`

      - `String data`

      - `JsonValue; type "redacted_thinking"constant`

        - `REDACTED_THINKING("redacted_thinking")`

    - `class BetaToolUseBlock:`

      - `String id`

      - `Input input`

      - `String name`

      - `JsonValue; type "tool_use"constant`

        - `TOOL_USE("tool_use")`

      - `Optional<Caller> caller`

        Tool invocation directly from the model.

        - `class BetaDirectCaller:`

          Tool invocation directly from the model.

          - `JsonValue; type "direct"constant`

            - `DIRECT("direct")`

        - `class BetaServerToolCaller:`

          Tool invocation generated by a server-side tool.

          - `String toolId`

          - `JsonValue; type "code_execution_20250825"constant`

            - `CODE_EXECUTION_20250825("code_execution_20250825")`

        - `class BetaServerToolCaller20260120:`

          - `String toolId`

          - `JsonValue; type "code_execution_20260120"constant`

            - `CODE_EXECUTION_20260120("code_execution_20260120")`

    - `class BetaServerToolUseBlock:`

      - `String id`

      - `Input input`

      - `Name name`

        - `ADVISOR("advisor")`

        - `WEB_SEARCH("web_search")`

        - `WEB_FETCH("web_fetch")`

        - `CODE_EXECUTION("code_execution")`

        - `BASH_CODE_EXECUTION("bash_code_execution")`

        - `TEXT_EDITOR_CODE_EXECUTION("text_editor_code_execution")`

        - `TOOL_SEARCH_TOOL_REGEX("tool_search_tool_regex")`

        - `TOOL_SEARCH_TOOL_BM25("tool_search_tool_bm25")`

      - `JsonValue; type "server_tool_use"constant`

        - `SERVER_TOOL_USE("server_tool_use")`

      - `Optional<Caller> caller`

        Tool invocation directly from the model.

        - `class BetaDirectCaller:`

          Tool invocation directly from the model.

        - `class BetaServerToolCaller:`

          Tool invocation generated by a server-side tool.

        - `class BetaServerToolCaller20260120:`

    - `class BetaWebSearchToolResultBlock:`

      - `BetaWebSearchToolResultBlockContent content`

        - `class BetaWebSearchToolResultError:`

          - `BetaWebSearchToolResultErrorCode errorCode`

            - `INVALID_TOOL_INPUT("invalid_tool_input")`

            - `UNAVAILABLE("unavailable")`

            - `MAX_USES_EXCEEDED("max_uses_exceeded")`

            - `TOO_MANY_REQUESTS("too_many_requests")`

            - `QUERY_TOO_LONG("query_too_long")`

            - `REQUEST_TOO_LARGE("request_too_large")`

          - `JsonValue; type "web_search_tool_result_error"constant`

            - `WEB_SEARCH_TOOL_RESULT_ERROR("web_search_tool_result_error")`

        - `List<BetaWebSearchResultBlock>`

          - `String encryptedContent`

          - `Optional<String> pageAge`

          - `String title`

          - `JsonValue; type "web_search_result"constant`

            - `WEB_SEARCH_RESULT("web_search_result")`

          - `String url`

      - `String toolUseId`

      - `JsonValue; type "web_search_tool_result"constant`

        - `WEB_SEARCH_TOOL_RESULT("web_search_tool_result")`

      - `Optional<Caller> caller`

        Tool invocation directly from the model.

        - `class BetaDirectCaller:`

          Tool invocation directly from the model.

        - `class BetaServerToolCaller:`

          Tool invocation generated by a server-side tool.

        - `class BetaServerToolCaller20260120:`

    - `class BetaWebFetchToolResultBlock:`

      - `Content content`

        - `class BetaWebFetchToolResultErrorBlock:`

          - `BetaWebFetchToolResultErrorCode errorCode`

            - `INVALID_TOOL_INPUT("invalid_tool_input")`

            - `URL_TOO_LONG("url_too_long")`

            - `URL_NOT_ALLOWED("url_not_allowed")`

            - `URL_NOT_IN_PRIOR_CONTEXT("url_not_in_prior_context")`

            - `URL_NOT_ACCESSIBLE("url_not_accessible")`

            - `UNSUPPORTED_CONTENT_TYPE("unsupported_content_type")`

            - `TOO_MANY_REQUESTS("too_many_requests")`

            - `MAX_USES_EXCEEDED("max_uses_exceeded")`

            - `UNAVAILABLE("unavailable")`

          - `JsonValue; type "web_fetch_tool_result_error"constant`

            - `WEB_FETCH_TOOL_RESULT_ERROR("web_fetch_tool_result_error")`

        - `class BetaWebFetchBlock:`

          - `BetaDocumentBlock content`

            - `Optional<BetaCitationConfig> citations`

              Citation configuration for the document

              - `boolean enabled`

            - `Source source`

              - `class BetaBase64PdfSource:`

                - `String data`

                - `JsonValue; mediaType "application/pdf"constant`

                  - `APPLICATION_PDF("application/pdf")`

                - `JsonValue; type "base64"constant`

                  - `BASE64("base64")`

              - `class BetaPlainTextSource:`

                - `String data`

                - `JsonValue; mediaType "text/plain"constant`

                  - `TEXT_PLAIN("text/plain")`

                - `JsonValue; type "text"constant`

                  - `TEXT("text")`

            - `Optional<String> title`

              The title of the document

            - `JsonValue; type "document"constant`

              - `DOCUMENT("document")`

          - `Optional<String> retrievedAt`

            ISO 8601 timestamp when the content was retrieved

          - `JsonValue; type "web_fetch_result"constant`

            - `WEB_FETCH_RESULT("web_fetch_result")`

          - `String url`

            Fetched content URL

      - `String toolUseId`

      - `JsonValue; type "web_fetch_tool_result"constant`

        - `WEB_FETCH_TOOL_RESULT("web_fetch_tool_result")`

      - `Optional<Caller> caller`

        Tool invocation directly from the model.

        - `class BetaDirectCaller:`

          Tool invocation directly from the model.

        - `class BetaServerToolCaller:`

          Tool invocation generated by a server-side tool.

        - `class BetaServerToolCaller20260120:`

    - `class BetaAdvisorToolResultBlock:`

      - `Content content`

        - `class BetaAdvisorToolResultError:`

          - `ErrorCode errorCode`

            - `MAX_USES_EXCEEDED("max_uses_exceeded")`

            - `PROMPT_TOO_LONG("prompt_too_long")`

            - `TOO_MANY_REQUESTS("too_many_requests")`

            - `OVERLOADED("overloaded")`

            - `UNAVAILABLE("unavailable")`

            - `EXECUTION_TIME_EXCEEDED("execution_time_exceeded")`

            - `MODEL_NOT_FOUND("model_not_found")`

          - `JsonValue; type "advisor_tool_result_error"constant`

            - `ADVISOR_TOOL_RESULT_ERROR("advisor_tool_result_error")`

        - `class BetaAdvisorResultBlock:`

          - `Optional<String> stopReason`

            The advisor sub-inference's stop reason (same values as the top-level message `stop_reason`). `max_tokens` indicates the advisor's output was truncated at the tool's `max_tokens` value or the advisor model's policy cap.

          - `String text`

          - `JsonValue; type "advisor_result"constant`

            - `ADVISOR_RESULT("advisor_result")`

        - `class BetaAdvisorRedactedResultBlock:`

          - `String encryptedContent`

            Opaque blob containing the advisor's output. Round-trip verbatim; do not inspect or modify.

          - `Optional<String> stopReason`

            The advisor sub-inference's stop reason (same values as the top-level message `stop_reason`).

          - `JsonValue; type "advisor_redacted_result"constant`

            - `ADVISOR_REDACTED_RESULT("advisor_redacted_result")`

      - `String toolUseId`

      - `JsonValue; type "advisor_tool_result"constant`

        - `ADVISOR_TOOL_RESULT("advisor_tool_result")`

    - `class BetaCodeExecutionToolResultBlock:`

      - `BetaCodeExecutionToolResultBlockContent content`

        Code execution result with encrypted stdout for PFC + web_search results.

        - `class BetaCodeExecutionToolResultError:`

          - `BetaCodeExecutionToolResultErrorCode errorCode`

            - `INVALID_TOOL_INPUT("invalid_tool_input")`

            - `UNAVAILABLE("unavailable")`

            - `TOO_MANY_REQUESTS("too_many_requests")`

            - `EXECUTION_TIME_EXCEEDED("execution_time_exceeded")`

          - `JsonValue; type "code_execution_tool_result_error"constant`

            - `CODE_EXECUTION_TOOL_RESULT_ERROR("code_execution_tool_result_error")`

        - `class BetaCodeExecutionResultBlock:`

          - `List<BetaCodeExecutionOutputBlock> content`

            - `String fileId`

            - `JsonValue; type "code_execution_output"constant`

              - `CODE_EXECUTION_OUTPUT("code_execution_output")`

          - `long returnCode`

          - `String stderr`

          - `String stdout`

          - `JsonValue; type "code_execution_result"constant`

            - `CODE_EXECUTION_RESULT("code_execution_result")`

        - `class BetaEncryptedCodeExecutionResultBlock:`

          Code execution result with encrypted stdout for PFC + web_search results.

          - `List<BetaCodeExecutionOutputBlock> content`

            - `String fileId`

            - `JsonValue; type "code_execution_output"constant`

          - `String encryptedStdout`

          - `long returnCode`

          - `String stderr`

          - `JsonValue; type "encrypted_code_execution_result"constant`

            - `ENCRYPTED_CODE_EXECUTION_RESULT("encrypted_code_execution_result")`

      - `String toolUseId`

      - `JsonValue; type "code_execution_tool_result"constant`

        - `CODE_EXECUTION_TOOL_RESULT("code_execution_tool_result")`

    - `class BetaBashCodeExecutionToolResultBlock:`

      - `Content content`

        - `class BetaBashCodeExecutionToolResultError:`

          - `ErrorCode errorCode`

            - `INVALID_TOOL_INPUT("invalid_tool_input")`

            - `UNAVAILABLE("unavailable")`

            - `TOO_MANY_REQUESTS("too_many_requests")`

            - `EXECUTION_TIME_EXCEEDED("execution_time_exceeded")`

            - `OUTPUT_FILE_TOO_LARGE("output_file_too_large")`

          - `JsonValue; type "bash_code_execution_tool_result_error"constant`

            - `BASH_CODE_EXECUTION_TOOL_RESULT_ERROR("bash_code_execution_tool_result_error")`

        - `class BetaBashCodeExecutionResultBlock:`

          - `List<BetaBashCodeExecutionOutputBlock> content`

            - `String fileId`

            - `JsonValue; type "bash_code_execution_output"constant`

              - `BASH_CODE_EXECUTION_OUTPUT("bash_code_execution_output")`

          - `long returnCode`

          - `String stderr`

          - `String stdout`

          - `JsonValue; type "bash_code_execution_result"constant`

            - `BASH_CODE_EXECUTION_RESULT("bash_code_execution_result")`

      - `String toolUseId`

      - `JsonValue; type "bash_code_execution_tool_result"constant`

        - `BASH_CODE_EXECUTION_TOOL_RESULT("bash_code_execution_tool_result")`

    - `class BetaTextEditorCodeExecutionToolResultBlock:`

      - `Content content`

        - `class BetaTextEditorCodeExecutionToolResultError:`

          - `ErrorCode errorCode`

            - `INVALID_TOOL_INPUT("invalid_tool_input")`

            - `UNAVAILABLE("unavailable")`

            - `TOO_MANY_REQUESTS("too_many_requests")`

            - `EXECUTION_TIME_EXCEEDED("execution_time_exceeded")`

            - `FILE_NOT_FOUND("file_not_found")`

          - `Optional<String> errorMessage`

          - `JsonValue; type "text_editor_code_execution_tool_result_error"constant`

            - `TEXT_EDITOR_CODE_EXECUTION_TOOL_RESULT_ERROR("text_editor_code_execution_tool_result_error")`

        - `class BetaTextEditorCodeExecutionViewResultBlock:`

          - `String content`

          - `FileType fileType`

            - `TEXT("text")`

            - `IMAGE("image")`

            - `PDF("pdf")`

          - `Optional<Long> numLines`

          - `Optional<Long> startLine`

          - `Optional<Long> totalLines`

          - `JsonValue; type "text_editor_code_execution_view_result"constant`

            - `TEXT_EDITOR_CODE_EXECUTION_VIEW_RESULT("text_editor_code_execution_view_result")`

        - `class BetaTextEditorCodeExecutionCreateResultBlock:`

          - `boolean isFileUpdate`

          - `JsonValue; type "text_editor_code_execution_create_result"constant`

            - `TEXT_EDITOR_CODE_EXECUTION_CREATE_RESULT("text_editor_code_execution_create_result")`

        - `class BetaTextEditorCodeExecutionStrReplaceResultBlock:`

          - `Optional<List<String>> lines`

          - `Optional<Long> newLines`

          - `Optional<Long> newStart`

          - `Optional<Long> oldLines`

          - `Optional<Long> oldStart`

          - `JsonValue; type "text_editor_code_execution_str_replace_result"constant`

            - `TEXT_EDITOR_CODE_EXECUTION_STR_REPLACE_RESULT("text_editor_code_execution_str_replace_result")`

      - `String toolUseId`

      - `JsonValue; type "text_editor_code_execution_tool_result"constant`

        - `TEXT_EDITOR_CODE_EXECUTION_TOOL_RESULT("text_editor_code_execution_tool_result")`

    - `class BetaToolSearchToolResultBlock:`

      - `Content content`

        - `class BetaToolSearchToolResultError:`

          - `ErrorCode errorCode`

            - `INVALID_TOOL_INPUT("invalid_tool_input")`

            - `UNAVAILABLE("unavailable")`

            - `TOO_MANY_REQUESTS("too_many_requests")`

            - `EXECUTION_TIME_EXCEEDED("execution_time_exceeded")`

          - `Optional<String> errorMessage`

          - `JsonValue; type "tool_search_tool_result_error"constant`

            - `TOOL_SEARCH_TOOL_RESULT_ERROR("tool_search_tool_result_error")`

        - `class BetaToolSearchToolSearchResultBlock:`

          - `List<BetaToolReferenceBlock> toolReferences`

            - `String toolName`

            - `JsonValue; type "tool_reference"constant`

              - `TOOL_REFERENCE("tool_reference")`

          - `JsonValue; type "tool_search_tool_search_result"constant`

            - `TOOL_SEARCH_TOOL_SEARCH_RESULT("tool_search_tool_search_result")`

      - `String toolUseId`

      - `JsonValue; type "tool_search_tool_result"constant`

        - `TOOL_SEARCH_TOOL_RESULT("tool_search_tool_result")`

    - `class BetaMcpToolUseBlock:`

      - `String id`

      - `Input input`

      - `String name`

        The name of the MCP tool

      - `String serverName`

        The name of the MCP server

      - `JsonValue; type "mcp_tool_use"constant`

        - `MCP_TOOL_USE("mcp_tool_use")`

    - `class BetaMcpToolResultBlock:`

      - `Content content`

        - `String`

        - `List<BetaTextBlock>`

          - `Optional<List<BetaTextCitation>> citations`

            Citations supporting the text block.

            The type of citation returned will depend on the type of document being cited. Citing a PDF results in `page_location`, plain text results in `char_location`, and content document results in `content_block_location`.

          - `String text`

          - `JsonValue; type "text"constant`

      - `boolean isError`

      - `String toolUseId`

      - `JsonValue; type "mcp_tool_result"constant`

        - `MCP_TOOL_RESULT("mcp_tool_result")`

    - `class BetaContainerUploadBlock:`

      Response model for a file uploaded to the container.

      - `String fileId`

      - `JsonValue; type "container_upload"constant`

        - `CONTAINER_UPLOAD("container_upload")`

    - `class BetaCompactionBlock:`

      A compaction block returned when autocompact is triggered.

      When content is None, it indicates the compaction failed to produce a valid
      summary (e.g., malformed output from the model). Clients may round-trip
      compaction blocks with null content; the server treats them as no-ops.

      - `Optional<String> content`

        Summary of compacted content, or null if compaction failed

      - `Optional<String> encryptedContent`

        Opaque metadata from prior compaction, to be round-tripped verbatim

      - `JsonValue; type "compaction"constant`

        - `COMPACTION("compaction")`

    - `class BetaFallbackBlock:`

      Marks the point in `content` where one model's output gives way to the next.

      One block appears per hop where a preceding model actually ran this turn and
      declined. A turn routed directly by the sticky decision has no such boundary
      and carries no block — the signal for whether a fallback model served the
      response is the presence of a `fallback_message` entry in
      `usage.iterations`, not this block.

      The block is treated like a server-tool content block for streaming: it
      arrives via the standard `content_block_start` / `content_block_stop`
      pair and carries no deltas.

      - `BetaFallbackInfo from`

        The model whose output ends at this point — the model that declined at this hop. When the declining hop is the requested model, its `model` echoes the top-level `model` string the caller sent (alias or canonical); when the declining hop is a fallback model, its `model` is that model's canonical id.

        - `Model model`

          The model that will complete your prompt.

          See [models](https://docs.anthropic.com/en/docs/models-overview) for additional details and options.

          - `CLAUDE_FABLE_5("claude-fable-5")`

            Next generation of intelligence for the hardest knowledge work and coding problems

          - `CLAUDE_MYTHOS_5("claude-mythos-5")`

            Most capable model for cybersecurity and biology research

          - `CLAUDE_OPUS_4_8("claude-opus-4-8")`

            Frontier intelligence for long-running agents and coding

          - `CLAUDE_OPUS_4_7("claude-opus-4-7")`

            Frontier intelligence for long-running agents and coding

          - `CLAUDE_MYTHOS_PREVIEW("claude-mythos-preview")`

            New class of intelligence, strongest in coding and cybersecurity

          - `CLAUDE_OPUS_4_6("claude-opus-4-6")`

            Frontier intelligence for long-running agents and coding

          - `CLAUDE_SONNET_4_6("claude-sonnet-4-6")`

            Best combination of speed and intelligence

          - `CLAUDE_HAIKU_4_5("claude-haiku-4-5")`

            Fastest model with near-frontier intelligence

          - `CLAUDE_HAIKU_4_5_20251001("claude-haiku-4-5-20251001")`

            Fastest model with near-frontier intelligence

          - `CLAUDE_OPUS_4_5("claude-opus-4-5")`

            Premium model combining maximum intelligence with practical performance

          - `CLAUDE_OPUS_4_5_20251101("claude-opus-4-5-20251101")`

            Premium model combining maximum intelligence with practical performance

          - `CLAUDE_SONNET_4_5("claude-sonnet-4-5")`

            High-performance model for agents and coding

          - `CLAUDE_SONNET_4_5_20250929("claude-sonnet-4-5-20250929")`

            High-performance model for agents and coding

          - `CLAUDE_OPUS_4_1("claude-opus-4-1")`

            Exceptional model for specialized complex tasks

          - `CLAUDE_OPUS_4_1_20250805("claude-opus-4-1-20250805")`

            Exceptional model for specialized complex tasks

          - `CLAUDE_OPUS_4_0("claude-opus-4-0")`

            Powerful model for complex tasks

          - `CLAUDE_OPUS_4_20250514("claude-opus-4-20250514")`

            Powerful model for complex tasks

          - `CLAUDE_SONNET_4_0("claude-sonnet-4-0")`

            High-performance model with extended thinking

          - `CLAUDE_SONNET_4_20250514("claude-sonnet-4-20250514")`

            High-performance model with extended thinking

          - `CLAUDE_3_HAIKU_20240307("claude-3-haiku-20240307")`

            Fast and cost-effective model

      - `BetaFallbackInfo to`

        The fallback model producing the content that follows this block. Its `model` is always the canonical id.

      - `JsonValue; type "fallback"constant`

        - `FALLBACK("fallback")`

  - `Optional<BetaContextManagementResponse> contextManagement`

    Context management response.

    Information about context management strategies applied during the request.

    - `List<AppliedEdit> appliedEdits`

      List of context management edits that were applied.

      - `class BetaClearToolUses20250919EditResponse:`

        - `long clearedInputTokens`

          Number of input tokens cleared by this edit.

        - `long clearedToolUses`

          Number of tool uses that were cleared.

        - `JsonValue; type "clear_tool_uses_20250919"constant`

          The type of context management edit applied.

          - `CLEAR_TOOL_USES_20250919("clear_tool_uses_20250919")`

      - `class BetaClearThinking20251015EditResponse:`

        - `long clearedInputTokens`

          Number of input tokens cleared by this edit.

        - `long clearedThinkingTurns`

          Number of thinking turns that were cleared.

        - `JsonValue; type "clear_thinking_20251015"constant`

          The type of context management edit applied.

          - `CLEAR_THINKING_20251015("clear_thinking_20251015")`

  - `Optional<BetaDiagnostics> diagnostics`

    Response envelope for request-level diagnostics. Present (possibly
    null) whenever the caller supplied `diagnostics` on the request.

    - `Optional<CacheMissReason> cacheMissReason`

      Explains why the prompt cache could not fully reuse the prefix from the request identified by `diagnostics.previous_message_id`. `null` means diagnosis is still pending — the response was serialized before the background comparison completed.

      - `class BetaCacheMissModelChanged:`

        - `long cacheMissedInputTokens`

          Approximate number of input tokens that would have been read from cache had the prefix matched the previous request.

        - `JsonValue; type "model_changed"constant`

          - `MODEL_CHANGED("model_changed")`

      - `class BetaCacheMissSystemChanged:`

        - `long cacheMissedInputTokens`

          Approximate number of input tokens that would have been read from cache had the prefix matched the previous request.

        - `JsonValue; type "system_changed"constant`

          - `SYSTEM_CHANGED("system_changed")`

      - `class BetaCacheMissToolsChanged:`

        - `long cacheMissedInputTokens`

          Approximate number of input tokens that would have been read from cache had the prefix matched the previous request.

        - `JsonValue; type "tools_changed"constant`

          - `TOOLS_CHANGED("tools_changed")`

      - `class BetaCacheMissMessagesChanged:`

        - `long cacheMissedInputTokens`

          Approximate number of input tokens that would have been read from cache had the prefix matched the previous request.

        - `JsonValue; type "messages_changed"constant`

          - `MESSAGES_CHANGED("messages_changed")`

      - `class BetaCacheMissPreviousMessageNotFound:`

        - `JsonValue; type "previous_message_not_found"constant`

          - `PREVIOUS_MESSAGE_NOT_FOUND("previous_message_not_found")`

      - `class BetaCacheMissUnavailable:`

        - `JsonValue; type "unavailable"constant`

          - `UNAVAILABLE("unavailable")`

  - `Model model`

    The model that will complete your prompt.

    See [models](https://docs.anthropic.com/en/docs/models-overview) for additional details and options.

  - `JsonValue; role "assistant"constant`

    Conversational role of the generated message.

    This will always be `"assistant"`.

    - `ASSISTANT("assistant")`

  - `Optional<BetaRefusalStopDetails> stopDetails`

    Structured information about a refusal.

    - `Optional<Category> category`

      The policy category that triggered the refusal.

      `null` when the refusal doesn't map to a named category.

      - `CYBER("cyber")`

      - `BIO("bio")`

      - `REASONING_EXTRACTION("reasoning_extraction")`

    - `Optional<String> explanation`

      Human-readable explanation of the refusal.

      This text is not guaranteed to be stable. `null` when no explanation is available for the category.

    - `Optional<String> fallbackCreditToken`

      Opaque code that refunds the cache-miss cost when retrying this refused
      request on the fallback model. Pass it as `fallback_credit_token` on the
      retry request. Expires 5 minutes after the refusal.

      The retry is sent either with the same request body (`system`, `messages`,
      `tools`, and other render-shaping fields), or with the same body plus one
      appended `assistant` message whose content is the partial text (with any
      trailing whitespace stripped from the final text block) and paired
      server-tool blocks from this refusal — which also authorizes that
      appended turn as an assistant-prefill continuation on models that otherwise
      disallow prefill. A token minted mid-server-tool-loop whose partial content
      was continuable may only be redeemed the second way — if a same-body retry
      is rejected with a 400 saying the token must be redeemed by continuing the
      partial response, retry the second way instead. Either way: same workspace,
      same platform; a mismatch is a 400. Resending a token for an already-warm
      prefix is permitted but yields no additional credit.

      `null` when the refused model isn't eligible for a fallback credit.

    - `Optional<Boolean> fallbackHasPrefillClaim`

      Whether the accompanying `fallback_credit_token` may be redeemed with the
      appended-assistant retry form. Only set when `fallback_credit_token` is
      present.

      `true`: retry by resending the same request body plus one appended
      `assistant` message whose content is this response's `content` with any
      trailing whitespace stripped from the final text block and unpaired
      `tool_use` blocks omitted (the same appended-turn shape described on
      `fallback_credit_token`), with the token attached. `false`: retry by
      resending the original request body unchanged, with the token attached —
      the appended-assistant form is not available for this refusal (no
      continuable partial content, or the request uses `output_format` or a
      `tool_choice` that forces tool use). One exception: when the request used
      `output_format` or a forced `tool_choice` and the refusal arrived after
      server tools (including MCP connector tools) had already executed, the
      token may not be redeemable by either retry form; if the exact-body retry
      is then rejected with a 400 saying the token must be redeemed by
      continuing the partial response, discard the token and retry without it.

      Advisory: if an appended-assistant retry is rejected with a 400 despite
      `true`, fall back to resending the original request body with the token.

    - `Optional<String> recommendedModel`

      The server's suggested retry target for this refusal. Populated when a fallback attempt could not be made (the fallback model's rate limit was exhausted, or it was overloaded); names the fallback model the caller can retry directly. Null otherwise.

    - `JsonValue; type "refusal"constant`

      - `REFUSAL("refusal")`

  - `Optional<BetaStopReason> stopReason`

    The reason that we stopped.

    This may be one the following values:

    * `"end_turn"`: the model reached a natural stopping point
    * `"max_tokens"`: we exceeded the requested `max_tokens` or the model's maximum
    * `"stop_sequence"`: one of your provided custom `stop_sequences` was generated
    * `"tool_use"`: the model invoked one or more tools
    * `"pause_turn"`: we paused a long-running turn. You may provide the response back as-is in a subsequent request to let the model continue.
    * `"refusal"`: when streaming classifiers intervene to handle potential policy violations

    In non-streaming mode this value is always non-null. In streaming mode, it is null in the `message_start` event and non-null otherwise.

    - `END_TURN("end_turn")`

    - `MAX_TOKENS("max_tokens")`

    - `STOP_SEQUENCE("stop_sequence")`

    - `TOOL_USE("tool_use")`

    - `PAUSE_TURN("pause_turn")`

    - `COMPACTION("compaction")`

    - `REFUSAL("refusal")`

    - `MODEL_CONTEXT_WINDOW_EXCEEDED("model_context_window_exceeded")`

  - `Optional<String> stopSequence`

    Which custom stop sequence was generated, if any.

    This value will be a non-null string if one of your custom stop sequences was generated.

  - `JsonValue; type "message"constant`

    Object type.

    For Messages, this is always `"message"`.

    - `MESSAGE("message")`

  - `BetaUsage usage`

    Billing and rate-limit usage.

    Anthropic's API bills and rate-limits by token counts, as tokens represent the underlying cost to our systems.

    Under the hood, the API transforms requests into a format suitable for the model. The model's output then goes through a parsing stage before becoming an API response. As a result, the token counts in `usage` will not match one-to-one with the exact visible content of an API request or response.

    For example, `output_tokens` will be non-zero, even for an empty string response from Claude.

    Total input tokens in a request is the summation of `input_tokens`, `cache_creation_input_tokens`, and `cache_read_input_tokens`.

    - `Optional<BetaCacheCreation> cacheCreation`

      Breakdown of cached tokens by TTL

      - `long ephemeral1hInputTokens`

        The number of input tokens used to create the 1 hour cache entry.

      - `long ephemeral5mInputTokens`

        The number of input tokens used to create the 5 minute cache entry.

    - `Optional<Long> cacheCreationInputTokens`

      The number of input tokens used to create the cache entry.

    - `Optional<Long> cacheReadInputTokens`

      The number of input tokens read from the cache.

    - `Optional<String> inferenceGeo`

      The geographic region where inference was performed for this request.

    - `long inputTokens`

      The number of input tokens which were used.

    - `Optional<List<BetaIterationsUsageItems>> iterations`

      Per-iteration token usage breakdown.

      Each entry represents one sampling iteration, with its own input/output token counts and cache statistics. This allows you to:

      - Determine which iterations exceeded long context thresholds (>=200k tokens)
      - Calculate the true context window size from the last iteration
      - Understand token accumulation across server-side tool use loops

      - `class BetaMessageIterationUsage:`

        Token usage for a sampling iteration.

        - `Optional<BetaCacheCreation> cacheCreation`

          Breakdown of cached tokens by TTL

        - `long cacheCreationInputTokens`

          The number of input tokens used to create the cache entry.

        - `long cacheReadInputTokens`

          The number of input tokens read from the cache.

        - `long inputTokens`

          The number of input tokens which were used.

        - `Model model`

          The model that will complete your prompt.

          See [models](https://docs.anthropic.com/en/docs/models-overview) for additional details and options.

        - `long outputTokens`

          The number of output tokens which were used.

        - `JsonValue; type "message"constant`

          Usage for a sampling iteration

          - `MESSAGE("message")`

      - `class BetaCompactionIterationUsage:`

        Token usage for a compaction iteration.

        - `Optional<BetaCacheCreation> cacheCreation`

          Breakdown of cached tokens by TTL

        - `long cacheCreationInputTokens`

          The number of input tokens used to create the cache entry.

        - `long cacheReadInputTokens`

          The number of input tokens read from the cache.

        - `long inputTokens`

          The number of input tokens which were used.

        - `long outputTokens`

          The number of output tokens which were used.

        - `JsonValue; type "compaction"constant`

          Usage for a compaction iteration

          - `COMPACTION("compaction")`

      - `class BetaAdvisorMessageIterationUsage:`

        Token usage for an advisor sub-inference iteration.

        - `Optional<BetaCacheCreation> cacheCreation`

          Breakdown of cached tokens by TTL

        - `long cacheCreationInputTokens`

          The number of input tokens used to create the cache entry.

        - `long cacheReadInputTokens`

          The number of input tokens read from the cache.

        - `long inputTokens`

          The number of input tokens which were used.

        - `Model model`

          The model that will complete your prompt.

          See [models](https://docs.anthropic.com/en/docs/models-overview) for additional details and options.

        - `long outputTokens`

          The number of output tokens which were used.

        - `JsonValue; type "advisor_message"constant`

          Usage for an advisor sub-inference iteration

          - `ADVISOR_MESSAGE("advisor_message")`

      - `class BetaFallbackMessageIterationUsage:`

        Token usage for the fallback-model attempt of a server-side fallback request.

        Produced in place of a `message` entry for whichever hop served the
        response. A declined hop produces the existing `message` entry. Whether
        a fallback model served the response is signalled by the presence of this
        entry in `usage.iterations`.

        - `Optional<BetaCacheCreation> cacheCreation`

          Breakdown of cached tokens by TTL

        - `long cacheCreationInputTokens`

          The number of input tokens used to create the cache entry.

        - `long cacheReadInputTokens`

          The number of input tokens read from the cache.

        - `long inputTokens`

          The number of input tokens which were used.

        - `Model model`

          The model that will complete your prompt.

          See [models](https://docs.anthropic.com/en/docs/models-overview) for additional details and options.

        - `long outputTokens`

          The number of output tokens which were used.

        - `JsonValue; type "fallback_message"constant`

          Usage for the fallback-model attempt that served the response

          - `FALLBACK_MESSAGE("fallback_message")`

    - `long outputTokens`

      The number of output tokens which were used.

    - `Optional<BetaOutputTokensDetails> outputTokensDetails`

      Breakdown of output tokens by category.

      `output_tokens` remains the inclusive, authoritative total used for billing.
      This object provides a read-only decomposition for observability — for example,
      how many of the billed output tokens were spent on internal reasoning that may
      have been summarized before being returned to you.

      - `long thinkingTokens`

        Number of output tokens the model generated as internal reasoning, including
        the thinking-block delimiter tokens.

        Reflects the raw reasoning the model produced, not the (possibly shorter)
        summarized thinking text returned in the response body. Computed by
        re-tokenizing the raw reasoning text, so it may differ from the model's exact
        generation count by a small number of tokens. Always ≤ `output_tokens`;
        `output_tokens - thinking_tokens` approximates the non-reasoning output.

    - `Optional<BetaServerToolUsage> serverToolUse`

      The number of server tool requests.

      - `long webFetchRequests`

        The number of web fetch tool requests.

      - `long webSearchRequests`

        The number of web search tool requests.

    - `Optional<ServiceTier> serviceTier`

      If the request used the priority, standard, or batch tier.

      - `STANDARD("standard")`

      - `PRIORITY("priority")`

      - `BATCH("batch")`

    - `Optional<Speed> speed`

      The inference speed mode used for this request.

      - `STANDARD("standard")`

      - `FAST("fast")`

### Example

```java
package com.anthropic.example;

import com.anthropic.client.AnthropicClient;
import com.anthropic.client.okhttp.AnthropicOkHttpClient;
import com.anthropic.models.beta.messages.BetaMessage;
import com.anthropic.models.beta.messages.MessageCreateParams;
import com.anthropic.models.messages.Model;

public final class Main {
    private Main() {}

    public static void main(String[] args) {
        AnthropicClient client = AnthropicOkHttpClient.fromEnv();

        MessageCreateParams params = MessageCreateParams.builder()
            .maxTokens(1024L)
            .addUserMessage("Hello, world")
            .model(Model.CLAUDE_OPUS_4_6)
            .build();
        BetaMessage betaMessage = client.beta().messages().create(params);
    }
}
```

#### Response

```json
{
  "id": "msg_013Zva2CMHLNnXjNJJKqJ2EF",
  "container": {
    "id": "id",
    "expires_at": "2019-12-27T18:11:19.117Z",
    "skills": [
      {
        "skill_id": "pdf",
        "type": "anthropic",
        "version": "latest"
      }
    ]
  },
  "content": [
    {
      "citations": [
        {
          "cited_text": "cited_text",
          "document_index": 0,
          "document_title": "document_title",
          "end_char_index": 0,
          "file_id": "file_id",
          "start_char_index": 0,
          "type": "char_location"
        }
      ],
      "text": "Hi! My name is Claude.",
      "type": "text"
    }
  ],
  "context_management": {
    "applied_edits": [
      {
        "cleared_input_tokens": 0,
        "cleared_tool_uses": 0,
        "type": "clear_tool_uses_20250919"
      }
    ]
  },
  "diagnostics": {
    "cache_miss_reason": {
      "cache_missed_input_tokens": 0,
      "type": "model_changed"
    }
  },
  "model": "claude-opus-4-6",
  "role": "assistant",
  "stop_details": {
    "category": "cyber",
    "explanation": "explanation",
    "fallback_credit_token": "fallback_credit_token",
    "fallback_has_prefill_claim": true,
    "recommended_model": "recommended_model",
    "type": "refusal"
  },
  "stop_reason": "end_turn",
  "stop_sequence": null,
  "type": "message",
  "usage": {
    "cache_creation": {
      "ephemeral_1h_input_tokens": 0,
      "ephemeral_5m_input_tokens": 0
    },
    "cache_creation_input_tokens": 2051,
    "cache_read_input_tokens": 2051,
    "inference_geo": "inference_geo",
    "input_tokens": 2095,
    "iterations": [
      {
        "cache_creation": {
          "ephemeral_1h_input_tokens": 0,
          "ephemeral_5m_input_tokens": 0
        },
        "cache_creation_input_tokens": 0,
        "cache_read_input_tokens": 0,
        "input_tokens": 0,
        "model": "claude-fable-5",
        "output_tokens": 0,
        "type": "message"
      }
    ],
    "output_tokens": 503,
    "output_tokens_details": {
      "thinking_tokens": 0
    },
    "server_tool_use": {
      "web_fetch_requests": 2,
      "web_search_requests": 0
    },
    "service_tier": "standard",
    "speed": "standard"
  }
}
```
