## Count tokens in a Message

`beta.messages.count_tokens(MessageCountTokensParams**kwargs)  -> BetaMessageTokensCount`

**post** `/v1/messages/count_tokens`

Count the number of tokens in a Message.

The Token Count API can be used to count the number of tokens in a Message, including tools, images, and documents, without creating it.

Learn more about token counting in our [user guide](https://docs.claude.com/en/docs/build-with-claude/token-counting)

### Parameters

- `messages: Iterable[BetaMessageParam]`

  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: Union[str, List[BetaContentBlockParam]]`

    - `str`

    - `List[BetaContentBlockParam]`

      - `class BetaTextBlockParam: …`

        - `text: str`

        - `type: Literal["text"]`

          - `"text"`

        - `cache_control: Optional[BetaCacheControlEphemeral]`

          Create a cache control breakpoint at this content block.

          - `type: Literal["ephemeral"]`

            - `"ephemeral"`

          - `ttl: Optional[Literal["5m", "1h"]]`

            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`.

            - `"5m"`

            - `"1h"`

        - `citations: Optional[List[BetaTextCitationParam]]`

          - `class BetaCitationCharLocationParam: …`

            - `cited_text: str`

            - `document_index: int`

            - `document_title: Optional[str]`

            - `end_char_index: int`

            - `start_char_index: int`

            - `type: Literal["char_location"]`

              - `"char_location"`

          - `class BetaCitationPageLocationParam: …`

            - `cited_text: str`

            - `document_index: int`

            - `document_title: Optional[str]`

            - `end_page_number: int`

            - `start_page_number: int`

            - `type: Literal["page_location"]`

              - `"page_location"`

          - `class BetaCitationContentBlockLocationParam: …`

            - `cited_text: str`

              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.

            - `document_index: int`

            - `document_title: Optional[str]`

            - `end_block_index: int`

              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`.

            - `start_block_index: int`

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

            - `type: Literal["content_block_location"]`

              - `"content_block_location"`

          - `class BetaCitationWebSearchResultLocationParam: …`

            - `cited_text: str`

            - `encrypted_index: str`

            - `title: Optional[str]`

            - `type: Literal["web_search_result_location"]`

              - `"web_search_result_location"`

            - `url: str`

          - `class BetaCitationSearchResultLocationParam: …`

            - `cited_text: str`

              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.

            - `end_block_index: int`

              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`.

            - `search_result_index: int`

              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.

            - `source: str`

            - `start_block_index: int`

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

            - `title: Optional[str]`

            - `type: Literal["search_result_location"]`

              - `"search_result_location"`

      - `class BetaImageBlockParam: …`

        - `source: Source`

          - `class BetaBase64ImageSource: …`

            - `data: str`

            - `media_type: Literal["image/jpeg", "image/png", "image/gif", "image/webp"]`

              - `"image/jpeg"`

              - `"image/png"`

              - `"image/gif"`

              - `"image/webp"`

            - `type: Literal["base64"]`

              - `"base64"`

          - `class BetaURLImageSource: …`

            - `type: Literal["url"]`

              - `"url"`

            - `url: str`

          - `class BetaFileImageSource: …`

            - `file_id: str`

            - `type: Literal["file"]`

              - `"file"`

        - `type: Literal["image"]`

          - `"image"`

        - `cache_control: Optional[BetaCacheControlEphemeral]`

          Create a cache control breakpoint at this content block.

      - `class BetaRequestDocumentBlock: …`

        - `source: Source`

          - `class BetaBase64PDFSource: …`

            - `data: str`

            - `media_type: Literal["application/pdf"]`

              - `"application/pdf"`

            - `type: Literal["base64"]`

              - `"base64"`

          - `class BetaPlainTextSource: …`

            - `data: str`

            - `media_type: Literal["text/plain"]`

              - `"text/plain"`

            - `type: Literal["text"]`

              - `"text"`

          - `class BetaContentBlockSource: …`

            - `content: Union[str, List[BetaContentBlockSourceContent]]`

              - `str`

              - `List[BetaContentBlockSourceContent]`

                - `class BetaTextBlockParam: …`

                - `class BetaImageBlockParam: …`

            - `type: Literal["content"]`

              - `"content"`

          - `class BetaURLPDFSource: …`

            - `type: Literal["url"]`

              - `"url"`

            - `url: str`

          - `class BetaFileDocumentSource: …`

            - `file_id: str`

            - `type: Literal["file"]`

              - `"file"`

        - `type: Literal["document"]`

          - `"document"`

        - `cache_control: Optional[BetaCacheControlEphemeral]`

          Create a cache control breakpoint at this content block.

        - `citations: Optional[BetaCitationsConfigParam]`

          - `enabled: Optional[bool]`

        - `context: Optional[str]`

        - `title: Optional[str]`

      - `class BetaSearchResultBlockParam: …`

        - `content: List[BetaTextBlockParam]`

          - `text: str`

          - `type: Literal["text"]`

          - `cache_control: Optional[BetaCacheControlEphemeral]`

            Create a cache control breakpoint at this content block.

          - `citations: Optional[List[BetaTextCitationParam]]`

        - `source: str`

        - `title: str`

        - `type: Literal["search_result"]`

          - `"search_result"`

        - `cache_control: Optional[BetaCacheControlEphemeral]`

          Create a cache control breakpoint at this content block.

        - `citations: Optional[BetaCitationsConfigParam]`

      - `class BetaThinkingBlockParam: …`

        - `signature: str`

        - `thinking: str`

        - `type: Literal["thinking"]`

          - `"thinking"`

      - `class BetaRedactedThinkingBlockParam: …`

        - `data: str`

        - `type: Literal["redacted_thinking"]`

          - `"redacted_thinking"`

      - `class BetaToolUseBlockParam: …`

        - `id: str`

        - `input: Dict[str, object]`

        - `name: str`

        - `type: Literal["tool_use"]`

          - `"tool_use"`

        - `cache_control: Optional[BetaCacheControlEphemeral]`

          Create a cache control breakpoint at this content block.

        - `caller: Optional[Caller]`

          Tool invocation directly from the model.

          - `class BetaDirectCaller: …`

            Tool invocation directly from the model.

            - `type: Literal["direct"]`

              - `"direct"`

          - `class BetaServerToolCaller: …`

            Tool invocation generated by a server-side tool.

            - `tool_id: str`

            - `type: Literal["code_execution_20250825"]`

              - `"code_execution_20250825"`

          - `class BetaServerToolCaller20260120: …`

            - `tool_id: str`

            - `type: Literal["code_execution_20260120"]`

              - `"code_execution_20260120"`

      - `class BetaToolResultBlockParam: …`

        - `tool_use_id: str`

        - `type: Literal["tool_result"]`

          - `"tool_result"`

        - `cache_control: Optional[BetaCacheControlEphemeral]`

          Create a cache control breakpoint at this content block.

        - `content: Optional[Union[str, List[Content], null]]`

          - `str`

          - `List[Content]`

            - `class BetaTextBlockParam: …`

            - `class BetaImageBlockParam: …`

            - `class BetaSearchResultBlockParam: …`

            - `class BetaRequestDocumentBlock: …`

            - `class BetaToolReferenceBlockParam: …`

              Tool reference block that can be included in tool_result content.

              - `tool_name: str`

              - `type: Literal["tool_reference"]`

                - `"tool_reference"`

              - `cache_control: Optional[BetaCacheControlEphemeral]`

                Create a cache control breakpoint at this content block.

        - `is_error: Optional[bool]`

      - `class BetaServerToolUseBlockParam: …`

        - `id: str`

        - `input: Dict[str, object]`

        - `name: Literal["advisor", "web_search", "web_fetch", 5 more]`

          - `"advisor"`

          - `"web_search"`

          - `"web_fetch"`

          - `"code_execution"`

          - `"bash_code_execution"`

          - `"text_editor_code_execution"`

          - `"tool_search_tool_regex"`

          - `"tool_search_tool_bm25"`

        - `type: Literal["server_tool_use"]`

          - `"server_tool_use"`

        - `cache_control: Optional[BetaCacheControlEphemeral]`

          Create a cache control breakpoint at this content block.

        - `caller: Optional[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: …`

        - `content: BetaWebSearchToolResultBlockParamContent`

          - `List[BetaWebSearchResultBlockParam]`

            - `encrypted_content: str`

            - `title: str`

            - `type: Literal["web_search_result"]`

              - `"web_search_result"`

            - `url: str`

            - `page_age: Optional[str]`

          - `class BetaWebSearchToolRequestError: …`

            - `error_code: BetaWebSearchToolResultErrorCode`

              - `"invalid_tool_input"`

              - `"unavailable"`

              - `"max_uses_exceeded"`

              - `"too_many_requests"`

              - `"query_too_long"`

              - `"request_too_large"`

            - `type: Literal["web_search_tool_result_error"]`

              - `"web_search_tool_result_error"`

        - `tool_use_id: str`

        - `type: Literal["web_search_tool_result"]`

          - `"web_search_tool_result"`

        - `cache_control: Optional[BetaCacheControlEphemeral]`

          Create a cache control breakpoint at this content block.

        - `caller: Optional[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: …`

            - `error_code: BetaWebFetchToolResultErrorCode`

              - `"invalid_tool_input"`

              - `"url_too_long"`

              - `"url_not_allowed"`

              - `"url_not_in_prior_context"`

              - `"url_not_accessible"`

              - `"unsupported_content_type"`

              - `"too_many_requests"`

              - `"max_uses_exceeded"`

              - `"unavailable"`

            - `type: Literal["web_fetch_tool_result_error"]`

              - `"web_fetch_tool_result_error"`

          - `class BetaWebFetchBlockParam: …`

            - `content: BetaRequestDocumentBlock`

            - `type: Literal["web_fetch_result"]`

              - `"web_fetch_result"`

            - `url: str`

              Fetched content URL

            - `retrieved_at: Optional[str]`

              ISO 8601 timestamp when the content was retrieved

        - `tool_use_id: str`

        - `type: Literal["web_fetch_tool_result"]`

          - `"web_fetch_tool_result"`

        - `cache_control: Optional[BetaCacheControlEphemeral]`

          Create a cache control breakpoint at this content block.

        - `caller: Optional[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: …`

            - `error_code: Literal["max_uses_exceeded", "prompt_too_long", "too_many_requests", 4 more]`

              - `"max_uses_exceeded"`

              - `"prompt_too_long"`

              - `"too_many_requests"`

              - `"overloaded"`

              - `"unavailable"`

              - `"execution_time_exceeded"`

              - `"model_not_found"`

            - `type: Literal["advisor_tool_result_error"]`

              - `"advisor_tool_result_error"`

          - `class BetaAdvisorResultBlockParam: …`

            - `text: str`

            - `type: Literal["advisor_result"]`

              - `"advisor_result"`

            - `stop_reason: Optional[str]`

          - `class BetaAdvisorRedactedResultBlockParam: …`

            - `encrypted_content: str`

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

            - `type: Literal["advisor_redacted_result"]`

              - `"advisor_redacted_result"`

            - `stop_reason: Optional[str]`

        - `tool_use_id: str`

        - `type: Literal["advisor_tool_result"]`

          - `"advisor_tool_result"`

        - `cache_control: Optional[BetaCacheControlEphemeral]`

          Create a cache control breakpoint at this content block.

      - `class BetaCodeExecutionToolResultBlockParam: …`

        - `content: BetaCodeExecutionToolResultBlockParamContent`

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

          - `class BetaCodeExecutionToolResultErrorParam: …`

            - `error_code: BetaCodeExecutionToolResultErrorCode`

              - `"invalid_tool_input"`

              - `"unavailable"`

              - `"too_many_requests"`

              - `"execution_time_exceeded"`

            - `type: Literal["code_execution_tool_result_error"]`

              - `"code_execution_tool_result_error"`

          - `class BetaCodeExecutionResultBlockParam: …`

            - `content: List[BetaCodeExecutionOutputBlockParam]`

              - `file_id: str`

              - `type: Literal["code_execution_output"]`

                - `"code_execution_output"`

            - `return_code: int`

            - `stderr: str`

            - `stdout: str`

            - `type: Literal["code_execution_result"]`

              - `"code_execution_result"`

          - `class BetaEncryptedCodeExecutionResultBlockParam: …`

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

            - `content: List[BetaCodeExecutionOutputBlockParam]`

              - `file_id: str`

              - `type: Literal["code_execution_output"]`

            - `encrypted_stdout: str`

            - `return_code: int`

            - `stderr: str`

            - `type: Literal["encrypted_code_execution_result"]`

              - `"encrypted_code_execution_result"`

        - `tool_use_id: str`

        - `type: Literal["code_execution_tool_result"]`

          - `"code_execution_tool_result"`

        - `cache_control: Optional[BetaCacheControlEphemeral]`

          Create a cache control breakpoint at this content block.

      - `class BetaBashCodeExecutionToolResultBlockParam: …`

        - `content: Content`

          - `class BetaBashCodeExecutionToolResultErrorParam: …`

            - `error_code: Literal["invalid_tool_input", "unavailable", "too_many_requests", 2 more]`

              - `"invalid_tool_input"`

              - `"unavailable"`

              - `"too_many_requests"`

              - `"execution_time_exceeded"`

              - `"output_file_too_large"`

            - `type: Literal["bash_code_execution_tool_result_error"]`

              - `"bash_code_execution_tool_result_error"`

          - `class BetaBashCodeExecutionResultBlockParam: …`

            - `content: List[BetaBashCodeExecutionOutputBlockParam]`

              - `file_id: str`

              - `type: Literal["bash_code_execution_output"]`

                - `"bash_code_execution_output"`

            - `return_code: int`

            - `stderr: str`

            - `stdout: str`

            - `type: Literal["bash_code_execution_result"]`

              - `"bash_code_execution_result"`

        - `tool_use_id: str`

        - `type: Literal["bash_code_execution_tool_result"]`

          - `"bash_code_execution_tool_result"`

        - `cache_control: Optional[BetaCacheControlEphemeral]`

          Create a cache control breakpoint at this content block.

      - `class BetaTextEditorCodeExecutionToolResultBlockParam: …`

        - `content: Content`

          - `class BetaTextEditorCodeExecutionToolResultErrorParam: …`

            - `error_code: Literal["invalid_tool_input", "unavailable", "too_many_requests", 2 more]`

              - `"invalid_tool_input"`

              - `"unavailable"`

              - `"too_many_requests"`

              - `"execution_time_exceeded"`

              - `"file_not_found"`

            - `type: Literal["text_editor_code_execution_tool_result_error"]`

              - `"text_editor_code_execution_tool_result_error"`

            - `error_message: Optional[str]`

          - `class BetaTextEditorCodeExecutionViewResultBlockParam: …`

            - `content: str`

            - `file_type: Literal["text", "image", "pdf"]`

              - `"text"`

              - `"image"`

              - `"pdf"`

            - `type: Literal["text_editor_code_execution_view_result"]`

              - `"text_editor_code_execution_view_result"`

            - `num_lines: Optional[int]`

            - `start_line: Optional[int]`

            - `total_lines: Optional[int]`

          - `class BetaTextEditorCodeExecutionCreateResultBlockParam: …`

            - `is_file_update: bool`

            - `type: Literal["text_editor_code_execution_create_result"]`

              - `"text_editor_code_execution_create_result"`

          - `class BetaTextEditorCodeExecutionStrReplaceResultBlockParam: …`

            - `type: Literal["text_editor_code_execution_str_replace_result"]`

              - `"text_editor_code_execution_str_replace_result"`

            - `lines: Optional[List[str]]`

            - `new_lines: Optional[int]`

            - `new_start: Optional[int]`

            - `old_lines: Optional[int]`

            - `old_start: Optional[int]`

        - `tool_use_id: str`

        - `type: Literal["text_editor_code_execution_tool_result"]`

          - `"text_editor_code_execution_tool_result"`

        - `cache_control: Optional[BetaCacheControlEphemeral]`

          Create a cache control breakpoint at this content block.

      - `class BetaToolSearchToolResultBlockParam: …`

        - `content: Content`

          - `class BetaToolSearchToolResultErrorParam: …`

            - `error_code: Literal["invalid_tool_input", "unavailable", "too_many_requests", "execution_time_exceeded"]`

              - `"invalid_tool_input"`

              - `"unavailable"`

              - `"too_many_requests"`

              - `"execution_time_exceeded"`

            - `type: Literal["tool_search_tool_result_error"]`

              - `"tool_search_tool_result_error"`

            - `error_message: Optional[str]`

          - `class BetaToolSearchToolSearchResultBlockParam: …`

            - `tool_references: List[BetaToolReferenceBlockParam]`

              - `tool_name: str`

              - `type: Literal["tool_reference"]`

              - `cache_control: Optional[BetaCacheControlEphemeral]`

                Create a cache control breakpoint at this content block.

            - `type: Literal["tool_search_tool_search_result"]`

              - `"tool_search_tool_search_result"`

        - `tool_use_id: str`

        - `type: Literal["tool_search_tool_result"]`

          - `"tool_search_tool_result"`

        - `cache_control: Optional[BetaCacheControlEphemeral]`

          Create a cache control breakpoint at this content block.

      - `class BetaMCPToolUseBlockParam: …`

        - `id: str`

        - `input: Dict[str, object]`

        - `name: str`

        - `server_name: str`

          The name of the MCP server

        - `type: Literal["mcp_tool_use"]`

          - `"mcp_tool_use"`

        - `cache_control: Optional[BetaCacheControlEphemeral]`

          Create a cache control breakpoint at this content block.

      - `class BetaRequestMCPToolResultBlockParam: …`

        - `tool_use_id: str`

        - `type: Literal["mcp_tool_result"]`

          - `"mcp_tool_result"`

        - `cache_control: Optional[BetaCacheControlEphemeral]`

          Create a cache control breakpoint at this content block.

        - `content: Optional[Union[str, List[BetaTextBlockParam], null]]`

          - `str`

          - `List[BetaTextBlockParam]`

            - `text: str`

            - `type: Literal["text"]`

            - `cache_control: Optional[BetaCacheControlEphemeral]`

              Create a cache control breakpoint at this content block.

            - `citations: Optional[List[BetaTextCitationParam]]`

        - `is_error: Optional[bool]`

      - `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.

        - `file_id: str`

        - `type: Literal["container_upload"]`

          - `"container_upload"`

        - `cache_control: Optional[BetaCacheControlEphemeral]`

          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.

        - `type: Literal["compaction"]`

          - `"compaction"`

        - `cache_control: Optional[BetaCacheControlEphemeral]`

          Create a cache control breakpoint at this content block.

        - `content: Optional[str]`

          Summary of previously compacted content, or null if compaction failed

        - `encrypted_content: Optional[str]`

          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.

        - `content: List[BetaTextBlockParam]`

          System instruction text blocks.

          - `text: str`

          - `type: Literal["text"]`

          - `cache_control: Optional[BetaCacheControlEphemeral]`

            Create a cache control breakpoint at this content block.

          - `citations: Optional[List[BetaTextCitationParam]]`

        - `type: Literal["mid_conv_system"]`

          - `"mid_conv_system"`

        - `cache_control: Optional[BetaCacheControlEphemeral]`

          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.

        - `from_: BetaFallbackInfoParam`

          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.

            - `Literal["claude-fable-5", "claude-mythos-5", "claude-opus-4-8", 17 more]`

              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` - Next generation of intelligence for the hardest knowledge work and coding problems
              - `claude-mythos-5` - Most capable model for cybersecurity and biology research
              - `claude-opus-4-8` - Frontier intelligence for long-running agents and coding
              - `claude-opus-4-7` - Frontier intelligence for long-running agents and coding
              - `claude-mythos-preview` - Deprecated: Will reach end-of-life on June 30, 2026. Please migrate to claude-mythos-5. Visit https://docs.anthropic.com/en/docs/resources/model-deprecations for more information.
              - `claude-opus-4-6` - Frontier intelligence for long-running agents and coding
              - `claude-sonnet-4-6` - Best combination of speed and intelligence
              - `claude-haiku-4-5` - Fastest model with near-frontier intelligence
              - `claude-haiku-4-5-20251001` - Fastest model with near-frontier intelligence
              - `claude-opus-4-5` - Premium model combining maximum intelligence with practical performance
              - `claude-opus-4-5-20251101` - Premium model combining maximum intelligence with practical performance
              - `claude-sonnet-4-5` - High-performance model for agents and coding
              - `claude-sonnet-4-5-20250929` - High-performance model for agents and coding
              - `claude-opus-4-1` - Deprecated: Will reach end-of-life on August 5, 2026. Please migrate to a newer model. Visit https://docs.anthropic.com/en/docs/resources/model-deprecations for more information.
              - `claude-opus-4-1-20250805` - Deprecated: Will reach end-of-life on August 5, 2026. Please migrate to a newer model. Visit https://docs.anthropic.com/en/docs/resources/model-deprecations for more information.
              - `claude-opus-4-0` - Deprecated: Will reach end-of-life on June 15th, 2026. Please migrate to a newer model. Visit https://docs.anthropic.com/en/docs/resources/model-deprecations for more information.
              - `claude-opus-4-20250514` - Deprecated: Will reach end-of-life on June 15th, 2026. Please migrate to a newer model. Visit https://docs.anthropic.com/en/docs/resources/model-deprecations for more information.
              - `claude-sonnet-4-0` - Deprecated: Will reach end-of-life on June 15th, 2026. Please migrate to a newer model. Visit https://docs.anthropic.com/en/docs/resources/model-deprecations for more information.
              - `claude-sonnet-4-20250514` - Deprecated: Will reach end-of-life on June 15th, 2026. Please migrate to a newer model. Visit https://docs.anthropic.com/en/docs/resources/model-deprecations for more information.
              - `claude-3-haiku-20240307` - Deprecated: Will reach end-of-life on April 20th, 2026. Please migrate to claude-haiku-4-5. Visit https://docs.anthropic.com/en/docs/resources/model-deprecations for more information.

              - `"claude-fable-5"`

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

              - `"claude-mythos-5"`

                Most capable model for cybersecurity and biology research

              - `"claude-opus-4-8"`

                Frontier intelligence for long-running agents and coding

              - `"claude-opus-4-7"`

                Frontier intelligence for long-running agents and coding

              - `"claude-mythos-preview"`

                New class of intelligence, strongest in coding and cybersecurity

              - `"claude-opus-4-6"`

                Frontier intelligence for long-running agents and coding

              - `"claude-sonnet-4-6"`

                Best combination of speed and intelligence

              - `"claude-haiku-4-5"`

                Fastest model with near-frontier intelligence

              - `"claude-haiku-4-5-20251001"`

                Fastest model with near-frontier intelligence

              - `"claude-opus-4-5"`

                Premium model combining maximum intelligence with practical performance

              - `"claude-opus-4-5-20251101"`

                Premium model combining maximum intelligence with practical performance

              - `"claude-sonnet-4-5"`

                High-performance model for agents and coding

              - `"claude-sonnet-4-5-20250929"`

                High-performance model for agents and coding

              - `"claude-opus-4-1"`

                Exceptional model for specialized complex tasks

              - `"claude-opus-4-1-20250805"`

                Exceptional model for specialized complex tasks

              - `"claude-opus-4-0"`

                Powerful model for complex tasks

              - `"claude-opus-4-20250514"`

                Powerful model for complex tasks

              - `"claude-sonnet-4-0"`

                High-performance model with extended thinking

              - `"claude-sonnet-4-20250514"`

                High-performance model with extended thinking

              - `"claude-3-haiku-20240307"`

                Fast and cost-effective model

            - `str`

        - `to: BetaFallbackInfoParam`

          Identifies one hop of a fallback transition.

        - `type: Literal["fallback"]`

          - `"fallback"`

  - `role: Literal["user", "assistant", "system"]`

    - `"user"`

    - `"assistant"`

    - `"system"`

- `model: ModelParam`

  The model that will complete your prompt.

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

- `cache_control: Optional[BetaCacheControlEphemeralParam]`

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

- `context_management: Optional[BetaContextManagementConfigParam]`

  Context management configuration.

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

  - `edits: Optional[List[Edit]]`

    List of context management edits to apply

    - `class BetaClearToolUses20250919Edit: …`

      - `type: Literal["clear_tool_uses_20250919"]`

        - `"clear_tool_uses_20250919"`

      - `clear_at_least: Optional[BetaInputTokensClearAtLeast]`

        Minimum number of tokens that must be cleared when triggered. Context will only be modified if at least this many tokens can be removed.

        - `type: Literal["input_tokens"]`

          - `"input_tokens"`

        - `value: int`

      - `clear_tool_inputs: Optional[Union[bool, List[str], null]]`

        Whether to clear all tool inputs (bool) or specific tool inputs to clear (list)

        - `bool`

        - `List[str]`

      - `exclude_tools: Optional[List[str]]`

        Tool names whose uses are preserved from clearing

      - `keep: Optional[BetaToolUsesKeep]`

        Number of tool uses to retain in the conversation

        - `type: Literal["tool_uses"]`

          - `"tool_uses"`

        - `value: int`

      - `trigger: Optional[Trigger]`

        Condition that triggers the context management strategy

        - `class BetaInputTokensTrigger: …`

          - `type: Literal["input_tokens"]`

            - `"input_tokens"`

          - `value: int`

        - `class BetaToolUsesTrigger: …`

          - `type: Literal["tool_uses"]`

            - `"tool_uses"`

          - `value: int`

    - `class BetaClearThinking20251015Edit: …`

      - `type: Literal["clear_thinking_20251015"]`

        - `"clear_thinking_20251015"`

      - `keep: Optional[Keep]`

        Number of most recent assistant turns to keep thinking blocks for. Older turns will have their thinking blocks removed.

        - `class BetaThinkingTurns: …`

          - `type: Literal["thinking_turns"]`

            - `"thinking_turns"`

          - `value: int`

        - `class BetaAllThinkingTurns: …`

          - `type: Literal["all"]`

            - `"all"`

        - `Literal["all"]`

          - `"all"`

    - `class BetaCompact20260112Edit: …`

      Automatically compact older context when reaching the configured trigger threshold.

      - `type: Literal["compact_20260112"]`

        - `"compact_20260112"`

      - `instructions: Optional[str]`

        Additional instructions for summarization.

      - `pause_after_compaction: Optional[bool]`

        Whether to pause after compaction and return the compaction block to the user.

      - `trigger: Optional[BetaInputTokensTrigger]`

        When to trigger compaction. Defaults to 150000 input tokens.

- `mcp_servers: Optional[Iterable[BetaRequestMCPServerURLDefinitionParam]]`

  MCP servers to be utilized in this request

  - `name: str`

  - `type: Literal["url"]`

    - `"url"`

  - `url: str`

  - `authorization_token: Optional[str]`

  - `tool_configuration: Optional[BetaRequestMCPServerToolConfiguration]`

    - `allowed_tools: Optional[List[str]]`

    - `enabled: Optional[bool]`

- `output_config: Optional[BetaOutputConfigParam]`

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

  - `effort: Optional[Literal["low", "medium", "high", 2 more]]`

    All possible effort levels.

    - `"low"`

    - `"medium"`

    - `"high"`

    - `"xhigh"`

    - `"max"`

  - `format: Optional[BetaJSONOutputFormat]`

    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: Dict[str, object]`

      The JSON schema of the format

    - `type: Literal["json_schema"]`

      - `"json_schema"`

  - `task_budget: Optional[BetaTokenTaskBudget]`

    User-configurable total token budget across contexts.

    - `total: int`

      Total token budget across all contexts in the session.

    - `type: Literal["tokens"]`

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

      - `"tokens"`

    - `remaining: Optional[int]`

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

- `output_format: Optional[BetaJSONOutputFormatParam]`

  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.

- `speed: Optional[Literal["standard", "fast"]]`

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

  - `"standard"`

  - `"fast"`

- `system: Optional[Union[str, Iterable[BetaTextBlockParam]]]`

  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).

  - `str`

  - `Iterable[BetaTextBlockParam]`

    - `text: str`

    - `type: Literal["text"]`

    - `cache_control: Optional[BetaCacheControlEphemeral]`

      Create a cache control breakpoint at this content block.

    - `citations: Optional[List[BetaTextCitationParam]]`

- `thinking: Optional[BetaThinkingConfigParam]`

  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.

  - `class BetaThinkingConfigEnabled: …`

    - `budget_tokens: int`

      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.

    - `type: Literal["enabled"]`

      - `"enabled"`

    - `display: Optional[Literal["summarized", "omitted"]]`

      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"`

      - `"omitted"`

  - `class BetaThinkingConfigDisabled: …`

    - `type: Literal["disabled"]`

      - `"disabled"`

  - `class BetaThinkingConfigAdaptive: …`

    - `type: Literal["adaptive"]`

      - `"adaptive"`

    - `display: Optional[Literal["summarized", "omitted"]]`

      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"`

      - `"omitted"`

- `tool_choice: Optional[BetaToolChoiceParam]`

  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.

  - `class BetaToolChoiceAuto: …`

    The model will automatically decide whether to use tools.

    - `type: Literal["auto"]`

      - `"auto"`

    - `disable_parallel_tool_use: Optional[bool]`

      Whether to disable parallel tool use.

      Defaults to `false`. If set to `true`, the model will output at most one tool use.

  - `class BetaToolChoiceAny: …`

    The model will use any available tools.

    - `type: Literal["any"]`

      - `"any"`

    - `disable_parallel_tool_use: Optional[bool]`

      Whether to disable parallel tool use.

      Defaults to `false`. If set to `true`, the model will output exactly one tool use.

  - `class BetaToolChoiceTool: …`

    The model will use the specified tool with `tool_choice.name`.

    - `name: str`

      The name of the tool to use.

    - `type: Literal["tool"]`

      - `"tool"`

    - `disable_parallel_tool_use: Optional[bool]`

      Whether to disable parallel tool use.

      Defaults to `false`. If set to `true`, the model will output exactly one tool use.

  - `class BetaToolChoiceNone: …`

    The model will not be allowed to use tools.

    - `type: Literal["none"]`

      - `"none"`

- `tools: Optional[Iterable[Tool]]`

  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: …`

    - `input_schema: 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.

      - `type: Literal["object"]`

        - `"object"`

      - `properties: Optional[Dict[str, object]]`

      - `required: Optional[List[str]]`

    - `name: str`

      Name of the tool.

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

    - `allowed_callers: Optional[List[Literal["direct", "code_execution_20250825", "code_execution_20260120"]]]`

      - `"direct"`

      - `"code_execution_20250825"`

      - `"code_execution_20260120"`

    - `cache_control: Optional[BetaCacheControlEphemeral]`

      Create a cache control breakpoint at this content block.

    - `defer_loading: Optional[bool]`

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

    - `description: Optional[str]`

      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.

    - `eager_input_streaming: Optional[bool]`

      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.

    - `input_examples: Optional[List[Dict[str, object]]]`

    - `strict: Optional[bool]`

      When true, guarantees schema validation on tool names and inputs

    - `type: Optional[Literal["custom"]]`

      - `"custom"`

  - `class BetaToolBash20241022: …`

    - `name: Literal["bash"]`

      Name of the tool.

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

      - `"bash"`

    - `type: Literal["bash_20241022"]`

      - `"bash_20241022"`

    - `allowed_callers: Optional[List[Literal["direct", "code_execution_20250825", "code_execution_20260120"]]]`

      - `"direct"`

      - `"code_execution_20250825"`

      - `"code_execution_20260120"`

    - `cache_control: Optional[BetaCacheControlEphemeral]`

      Create a cache control breakpoint at this content block.

    - `defer_loading: Optional[bool]`

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

    - `input_examples: Optional[List[Dict[str, object]]]`

    - `strict: Optional[bool]`

      When true, guarantees schema validation on tool names and inputs

  - `class BetaToolBash20250124: …`

    - `name: Literal["bash"]`

      Name of the tool.

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

      - `"bash"`

    - `type: Literal["bash_20250124"]`

      - `"bash_20250124"`

    - `allowed_callers: Optional[List[Literal["direct", "code_execution_20250825", "code_execution_20260120"]]]`

      - `"direct"`

      - `"code_execution_20250825"`

      - `"code_execution_20260120"`

    - `cache_control: Optional[BetaCacheControlEphemeral]`

      Create a cache control breakpoint at this content block.

    - `defer_loading: Optional[bool]`

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

    - `input_examples: Optional[List[Dict[str, object]]]`

    - `strict: Optional[bool]`

      When true, guarantees schema validation on tool names and inputs

  - `class BetaCodeExecutionTool20250522: …`

    - `name: Literal["code_execution"]`

      Name of the tool.

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

      - `"code_execution"`

    - `type: Literal["code_execution_20250522"]`

      - `"code_execution_20250522"`

    - `allowed_callers: Optional[List[Literal["direct", "code_execution_20250825", "code_execution_20260120"]]]`

      - `"direct"`

      - `"code_execution_20250825"`

      - `"code_execution_20260120"`

    - `cache_control: Optional[BetaCacheControlEphemeral]`

      Create a cache control breakpoint at this content block.

    - `defer_loading: Optional[bool]`

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

    - `strict: Optional[bool]`

      When true, guarantees schema validation on tool names and inputs

  - `class BetaCodeExecutionTool20250825: …`

    - `name: Literal["code_execution"]`

      Name of the tool.

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

      - `"code_execution"`

    - `type: Literal["code_execution_20250825"]`

      - `"code_execution_20250825"`

    - `allowed_callers: Optional[List[Literal["direct", "code_execution_20250825", "code_execution_20260120"]]]`

      - `"direct"`

      - `"code_execution_20250825"`

      - `"code_execution_20260120"`

    - `cache_control: Optional[BetaCacheControlEphemeral]`

      Create a cache control breakpoint at this content block.

    - `defer_loading: Optional[bool]`

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

    - `strict: Optional[bool]`

      When true, guarantees schema validation on tool names and inputs

  - `class BetaCodeExecutionTool20260120: …`

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

    - `name: Literal["code_execution"]`

      Name of the tool.

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

      - `"code_execution"`

    - `type: Literal["code_execution_20260120"]`

      - `"code_execution_20260120"`

    - `allowed_callers: Optional[List[Literal["direct", "code_execution_20250825", "code_execution_20260120"]]]`

      - `"direct"`

      - `"code_execution_20250825"`

      - `"code_execution_20260120"`

    - `cache_control: Optional[BetaCacheControlEphemeral]`

      Create a cache control breakpoint at this content block.

    - `defer_loading: Optional[bool]`

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

    - `strict: Optional[bool]`

      When true, guarantees schema validation on tool names and inputs

  - `class BetaToolComputerUse20241022: …`

    - `display_height_px: int`

      The height of the display in pixels.

    - `display_width_px: int`

      The width of the display in pixels.

    - `name: Literal["computer"]`

      Name of the tool.

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

      - `"computer"`

    - `type: Literal["computer_20241022"]`

      - `"computer_20241022"`

    - `allowed_callers: Optional[List[Literal["direct", "code_execution_20250825", "code_execution_20260120"]]]`

      - `"direct"`

      - `"code_execution_20250825"`

      - `"code_execution_20260120"`

    - `cache_control: Optional[BetaCacheControlEphemeral]`

      Create a cache control breakpoint at this content block.

    - `defer_loading: Optional[bool]`

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

    - `display_number: Optional[int]`

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

    - `input_examples: Optional[List[Dict[str, object]]]`

    - `strict: Optional[bool]`

      When true, guarantees schema validation on tool names and inputs

  - `class BetaMemoryTool20250818: …`

    - `name: Literal["memory"]`

      Name of the tool.

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

      - `"memory"`

    - `type: Literal["memory_20250818"]`

      - `"memory_20250818"`

    - `allowed_callers: Optional[List[Literal["direct", "code_execution_20250825", "code_execution_20260120"]]]`

      - `"direct"`

      - `"code_execution_20250825"`

      - `"code_execution_20260120"`

    - `cache_control: Optional[BetaCacheControlEphemeral]`

      Create a cache control breakpoint at this content block.

    - `defer_loading: Optional[bool]`

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

    - `input_examples: Optional[List[Dict[str, object]]]`

    - `strict: Optional[bool]`

      When true, guarantees schema validation on tool names and inputs

  - `class BetaToolComputerUse20250124: …`

    - `display_height_px: int`

      The height of the display in pixels.

    - `display_width_px: int`

      The width of the display in pixels.

    - `name: Literal["computer"]`

      Name of the tool.

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

      - `"computer"`

    - `type: Literal["computer_20250124"]`

      - `"computer_20250124"`

    - `allowed_callers: Optional[List[Literal["direct", "code_execution_20250825", "code_execution_20260120"]]]`

      - `"direct"`

      - `"code_execution_20250825"`

      - `"code_execution_20260120"`

    - `cache_control: Optional[BetaCacheControlEphemeral]`

      Create a cache control breakpoint at this content block.

    - `defer_loading: Optional[bool]`

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

    - `display_number: Optional[int]`

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

    - `input_examples: Optional[List[Dict[str, object]]]`

    - `strict: Optional[bool]`

      When true, guarantees schema validation on tool names and inputs

  - `class BetaToolTextEditor20241022: …`

    - `name: Literal["str_replace_editor"]`

      Name of the tool.

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

      - `"str_replace_editor"`

    - `type: Literal["text_editor_20241022"]`

      - `"text_editor_20241022"`

    - `allowed_callers: Optional[List[Literal["direct", "code_execution_20250825", "code_execution_20260120"]]]`

      - `"direct"`

      - `"code_execution_20250825"`

      - `"code_execution_20260120"`

    - `cache_control: Optional[BetaCacheControlEphemeral]`

      Create a cache control breakpoint at this content block.

    - `defer_loading: Optional[bool]`

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

    - `input_examples: Optional[List[Dict[str, object]]]`

    - `strict: Optional[bool]`

      When true, guarantees schema validation on tool names and inputs

  - `class BetaToolComputerUse20251124: …`

    - `display_height_px: int`

      The height of the display in pixels.

    - `display_width_px: int`

      The width of the display in pixels.

    - `name: Literal["computer"]`

      Name of the tool.

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

      - `"computer"`

    - `type: Literal["computer_20251124"]`

      - `"computer_20251124"`

    - `allowed_callers: Optional[List[Literal["direct", "code_execution_20250825", "code_execution_20260120"]]]`

      - `"direct"`

      - `"code_execution_20250825"`

      - `"code_execution_20260120"`

    - `cache_control: Optional[BetaCacheControlEphemeral]`

      Create a cache control breakpoint at this content block.

    - `defer_loading: Optional[bool]`

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

    - `display_number: Optional[int]`

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

    - `enable_zoom: Optional[bool]`

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

    - `input_examples: Optional[List[Dict[str, object]]]`

    - `strict: Optional[bool]`

      When true, guarantees schema validation on tool names and inputs

  - `class BetaToolTextEditor20250124: …`

    - `name: Literal["str_replace_editor"]`

      Name of the tool.

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

      - `"str_replace_editor"`

    - `type: Literal["text_editor_20250124"]`

      - `"text_editor_20250124"`

    - `allowed_callers: Optional[List[Literal["direct", "code_execution_20250825", "code_execution_20260120"]]]`

      - `"direct"`

      - `"code_execution_20250825"`

      - `"code_execution_20260120"`

    - `cache_control: Optional[BetaCacheControlEphemeral]`

      Create a cache control breakpoint at this content block.

    - `defer_loading: Optional[bool]`

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

    - `input_examples: Optional[List[Dict[str, object]]]`

    - `strict: Optional[bool]`

      When true, guarantees schema validation on tool names and inputs

  - `class BetaToolTextEditor20250429: …`

    - `name: Literal["str_replace_based_edit_tool"]`

      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"`

    - `type: Literal["text_editor_20250429"]`

      - `"text_editor_20250429"`

    - `allowed_callers: Optional[List[Literal["direct", "code_execution_20250825", "code_execution_20260120"]]]`

      - `"direct"`

      - `"code_execution_20250825"`

      - `"code_execution_20260120"`

    - `cache_control: Optional[BetaCacheControlEphemeral]`

      Create a cache control breakpoint at this content block.

    - `defer_loading: Optional[bool]`

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

    - `input_examples: Optional[List[Dict[str, object]]]`

    - `strict: Optional[bool]`

      When true, guarantees schema validation on tool names and inputs

  - `class BetaToolTextEditor20250728: …`

    - `name: Literal["str_replace_based_edit_tool"]`

      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"`

    - `type: Literal["text_editor_20250728"]`

      - `"text_editor_20250728"`

    - `allowed_callers: Optional[List[Literal["direct", "code_execution_20250825", "code_execution_20260120"]]]`

      - `"direct"`

      - `"code_execution_20250825"`

      - `"code_execution_20260120"`

    - `cache_control: Optional[BetaCacheControlEphemeral]`

      Create a cache control breakpoint at this content block.

    - `defer_loading: Optional[bool]`

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

    - `input_examples: Optional[List[Dict[str, object]]]`

    - `max_characters: Optional[int]`

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

    - `strict: Optional[bool]`

      When true, guarantees schema validation on tool names and inputs

  - `class BetaWebSearchTool20250305: …`

    - `name: Literal["web_search"]`

      Name of the tool.

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

      - `"web_search"`

    - `type: Literal["web_search_20250305"]`

      - `"web_search_20250305"`

    - `allowed_callers: Optional[List[Literal["direct", "code_execution_20250825", "code_execution_20260120"]]]`

      - `"direct"`

      - `"code_execution_20250825"`

      - `"code_execution_20260120"`

    - `allowed_domains: Optional[List[str]]`

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

    - `blocked_domains: Optional[List[str]]`

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

    - `cache_control: Optional[BetaCacheControlEphemeral]`

      Create a cache control breakpoint at this content block.

    - `defer_loading: Optional[bool]`

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

    - `max_uses: Optional[int]`

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

    - `strict: Optional[bool]`

      When true, guarantees schema validation on tool names and inputs

    - `user_location: Optional[BetaUserLocation]`

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

      - `type: Literal["approximate"]`

        - `"approximate"`

      - `city: Optional[str]`

        The city of the user.

      - `country: Optional[str]`

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

      - `region: Optional[str]`

        The region of the user.

      - `timezone: Optional[str]`

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

  - `class BetaWebFetchTool20250910: …`

    - `name: Literal["web_fetch"]`

      Name of the tool.

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

      - `"web_fetch"`

    - `type: Literal["web_fetch_20250910"]`

      - `"web_fetch_20250910"`

    - `allowed_callers: Optional[List[Literal["direct", "code_execution_20250825", "code_execution_20260120"]]]`

      - `"direct"`

      - `"code_execution_20250825"`

      - `"code_execution_20260120"`

    - `allowed_domains: Optional[List[str]]`

      List of domains to allow fetching from

    - `blocked_domains: Optional[List[str]]`

      List of domains to block fetching from

    - `cache_control: Optional[BetaCacheControlEphemeral]`

      Create a cache control breakpoint at this content block.

    - `citations: Optional[BetaCitationsConfigParam]`

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

    - `defer_loading: Optional[bool]`

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

    - `max_content_tokens: Optional[int]`

      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.

    - `max_uses: Optional[int]`

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

    - `strict: Optional[bool]`

      When true, guarantees schema validation on tool names and inputs

  - `class BetaWebSearchTool20260209: …`

    - `name: Literal["web_search"]`

      Name of the tool.

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

      - `"web_search"`

    - `type: Literal["web_search_20260209"]`

      - `"web_search_20260209"`

    - `allowed_callers: Optional[List[Literal["direct", "code_execution_20250825", "code_execution_20260120"]]]`

      - `"direct"`

      - `"code_execution_20250825"`

      - `"code_execution_20260120"`

    - `allowed_domains: Optional[List[str]]`

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

    - `blocked_domains: Optional[List[str]]`

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

    - `cache_control: Optional[BetaCacheControlEphemeral]`

      Create a cache control breakpoint at this content block.

    - `defer_loading: Optional[bool]`

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

    - `max_uses: Optional[int]`

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

    - `strict: Optional[bool]`

      When true, guarantees schema validation on tool names and inputs

    - `user_location: Optional[BetaUserLocation]`

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

  - `class BetaWebFetchTool20260209: …`

    - `name: Literal["web_fetch"]`

      Name of the tool.

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

      - `"web_fetch"`

    - `type: Literal["web_fetch_20260209"]`

      - `"web_fetch_20260209"`

    - `allowed_callers: Optional[List[Literal["direct", "code_execution_20250825", "code_execution_20260120"]]]`

      - `"direct"`

      - `"code_execution_20250825"`

      - `"code_execution_20260120"`

    - `allowed_domains: Optional[List[str]]`

      List of domains to allow fetching from

    - `blocked_domains: Optional[List[str]]`

      List of domains to block fetching from

    - `cache_control: Optional[BetaCacheControlEphemeral]`

      Create a cache control breakpoint at this content block.

    - `citations: Optional[BetaCitationsConfigParam]`

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

    - `defer_loading: Optional[bool]`

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

    - `max_content_tokens: Optional[int]`

      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.

    - `max_uses: Optional[int]`

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

    - `strict: Optional[bool]`

      When true, guarantees schema validation on tool names and inputs

  - `class BetaWebFetchTool20260309: …`

    Web fetch tool with use_cache parameter for bypassing cached content.

    - `name: Literal["web_fetch"]`

      Name of the tool.

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

      - `"web_fetch"`

    - `type: Literal["web_fetch_20260309"]`

      - `"web_fetch_20260309"`

    - `allowed_callers: Optional[List[Literal["direct", "code_execution_20250825", "code_execution_20260120"]]]`

      - `"direct"`

      - `"code_execution_20250825"`

      - `"code_execution_20260120"`

    - `allowed_domains: Optional[List[str]]`

      List of domains to allow fetching from

    - `blocked_domains: Optional[List[str]]`

      List of domains to block fetching from

    - `cache_control: Optional[BetaCacheControlEphemeral]`

      Create a cache control breakpoint at this content block.

    - `citations: Optional[BetaCitationsConfigParam]`

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

    - `defer_loading: Optional[bool]`

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

    - `max_content_tokens: Optional[int]`

      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.

    - `max_uses: Optional[int]`

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

    - `strict: Optional[bool]`

      When true, guarantees schema validation on tool names and inputs

    - `use_cache: Optional[bool]`

      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.

    - `name: Literal["advisor"]`

      Name of the tool.

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

      - `"advisor"`

    - `type: Literal["advisor_20260301"]`

      - `"advisor_20260301"`

    - `allowed_callers: Optional[List[Literal["direct", "code_execution_20250825", "code_execution_20260120"]]]`

      - `"direct"`

      - `"code_execution_20250825"`

      - `"code_execution_20260120"`

    - `cache_control: Optional[BetaCacheControlEphemeral]`

      Create a cache control breakpoint at this content block.

    - `caching: Optional[BetaCacheControlEphemeral]`

      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.

    - `defer_loading: Optional[bool]`

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

    - `max_tokens: Optional[int]`

      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.

    - `max_uses: Optional[int]`

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

    - `strict: Optional[bool]`

      When true, guarantees schema validation on tool names and inputs

  - `class BetaToolSearchToolBm25_20251119: …`

    - `name: Literal["tool_search_tool_bm25"]`

      Name of the tool.

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

      - `"tool_search_tool_bm25"`

    - `type: Literal["tool_search_tool_bm25_20251119", "tool_search_tool_bm25"]`

      - `"tool_search_tool_bm25_20251119"`

      - `"tool_search_tool_bm25"`

    - `allowed_callers: Optional[List[Literal["direct", "code_execution_20250825", "code_execution_20260120"]]]`

      - `"direct"`

      - `"code_execution_20250825"`

      - `"code_execution_20260120"`

    - `cache_control: Optional[BetaCacheControlEphemeral]`

      Create a cache control breakpoint at this content block.

    - `defer_loading: Optional[bool]`

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

    - `strict: Optional[bool]`

      When true, guarantees schema validation on tool names and inputs

  - `class BetaToolSearchToolRegex20251119: …`

    - `name: Literal["tool_search_tool_regex"]`

      Name of the tool.

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

      - `"tool_search_tool_regex"`

    - `type: Literal["tool_search_tool_regex_20251119", "tool_search_tool_regex"]`

      - `"tool_search_tool_regex_20251119"`

      - `"tool_search_tool_regex"`

    - `allowed_callers: Optional[List[Literal["direct", "code_execution_20250825", "code_execution_20260120"]]]`

      - `"direct"`

      - `"code_execution_20250825"`

      - `"code_execution_20260120"`

    - `cache_control: Optional[BetaCacheControlEphemeral]`

      Create a cache control breakpoint at this content block.

    - `defer_loading: Optional[bool]`

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

    - `strict: Optional[bool]`

      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.

    - `mcp_server_name: str`

      Name of the MCP server to configure tools for

    - `type: Literal["mcp_toolset"]`

      - `"mcp_toolset"`

    - `cache_control: Optional[BetaCacheControlEphemeral]`

      Create a cache control breakpoint at this content block.

    - `configs: Optional[Dict[str, BetaMCPToolConfig]]`

      Configuration overrides for specific tools, keyed by tool name

      - `defer_loading: Optional[bool]`

      - `enabled: Optional[bool]`

    - `default_config: Optional[BetaMCPToolDefaultConfig]`

      Default configuration applied to all tools from this server

      - `defer_loading: Optional[bool]`

      - `enabled: Optional[bool]`

- `betas: Optional[List[AnthropicBetaParam]]`

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

  - `str`

  - `Literal["message-batches-2024-09-24", "prompt-caching-2024-07-31", "computer-use-2024-10-22", 25 more]`

    - `"message-batches-2024-09-24"`

    - `"prompt-caching-2024-07-31"`

    - `"computer-use-2024-10-22"`

    - `"computer-use-2025-01-24"`

    - `"pdfs-2024-09-25"`

    - `"token-counting-2024-11-01"`

    - `"token-efficient-tools-2025-02-19"`

    - `"output-128k-2025-02-19"`

    - `"files-api-2025-04-14"`

    - `"mcp-client-2025-04-04"`

    - `"mcp-client-2025-11-20"`

    - `"dev-full-thinking-2025-05-14"`

    - `"interleaved-thinking-2025-05-14"`

    - `"code-execution-2025-05-22"`

    - `"extended-cache-ttl-2025-04-11"`

    - `"context-1m-2025-08-07"`

    - `"context-management-2025-06-27"`

    - `"model-context-window-exceeded-2025-08-26"`

    - `"skills-2025-10-02"`

    - `"fast-mode-2026-02-01"`

    - `"output-300k-2026-03-24"`

    - `"user-profiles-2026-03-24"`

    - `"advisor-tool-2026-03-01"`

    - `"managed-agents-2026-04-01"`

    - `"cache-diagnosis-2026-04-07"`

    - `"thinking-token-count-2026-05-13"`

    - `"server-side-fallback-2026-06-01"`

    - `"fallback-credit-2026-06-01"`

### Returns

- `class BetaMessageTokensCount: …`

  - `context_management: Optional[BetaCountTokensContextManagementResponse]`

    Information about context management applied to the message.

    - `original_input_tokens: int`

      The original token count before context management was applied

  - `input_tokens: int`

    The total number of tokens across the provided list of messages, system prompt, and tools.

### Example

```python
import os
from anthropic import Anthropic

client = Anthropic(
    api_key=os.environ.get("ANTHROPIC_API_KEY"),  # This is the default and can be omitted
)
beta_message_tokens_count = client.beta.messages.count_tokens(
    messages=[{
        "content": "Hello, world",
        "role": "user",
    }],
    model="claude-opus-4-6",
)
print(beta_message_tokens_count.context_management)
```

#### Response

```json
{
  "context_management": {
    "original_input_tokens": 0
  },
  "input_tokens": 2095
}
```
