> ## Documentation Index
> Fetch the complete documentation index at: https://modelcontextprotocol.io/llms.txt
> Use this file to discover all available pages before exploring further.

# Key Changes

This document lists changes made to the Model Context Protocol (MCP) specification since
the previous revision, [2024-11-05](/specification/2024-11-05).

## Major changes

1. Added a comprehensive **[authorization framework](/specification/2025-03-26/basic/authorization)**
   based on OAuth 2.1 (PR
   [#133](https://github.com/modelcontextprotocol/specification/pull/133))
2. Replaced the previous HTTP+SSE transport with a more flexible **[Streamable HTTP
   transport](/specification/2025-03-26/basic/transports#streamable-http)** (PR
   [#206](https://github.com/modelcontextprotocol/specification/pull/206))
3. Added support for JSON-RPC **[batching](https://www.jsonrpc.org/specification#batch)**
   (PR [#228](https://github.com/modelcontextprotocol/specification/pull/228))
4. Added comprehensive **tool annotations** for better describing tool behavior, like
   whether it is read-only or destructive (PR
   [#185](https://github.com/modelcontextprotocol/specification/pull/185))

## Other schema changes

* Added `message` field to `ProgressNotification` to provide descriptive status updates
* Added support for audio data, joining the existing text and image content types
* Added `completions` capability to explicitly indicate support for argument
  autocompletion suggestions

See
[the updated schema](http://github.com/modelcontextprotocol/specification/tree/main/schema/2025-03-26/schema.ts)
for more details.

## Full changelog

For a complete list of all changes that have been made since the last protocol revision,
[see GitHub](https://github.com/modelcontextprotocol/specification/compare/2024-11-05...2025-03-26).
