MCP 2025-03-26 lands: Streamable HTTP and OAuth 2.1 authorization
The protocol's second specification revision replaced the original HTTP+SSE transport with Streamable HTTP, added a comprehensive OAuth 2.1 authorization framework, and introduced JSON-RPC batching and tool annotations.
The 2025-03-26 revision was the Model Context Protocol's first major update after launch, and the one that made remote servers practical. It replaced the original HTTP+SSE transport with Streamable HTTP, removing the need for persistent connections, and added the protocol's first comprehensive authorization framework, based on OAuth 2.1.
The revision also added JSON-RPC batching (removed again in the following revision), tool annotations describing tool behavior such as read-only versus destructive, audio content support, and a completions capability. The full change list is recorded on the MCP 2025-03-26 revision page.
Related spec revisions
- MCP 2025-03-26 - superseded
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Published · last verified · confidence 1.00.