MCP Python SDK v2.1.0 — StdioServerParameters in Client, Image/Audio in prompts, TypedDict results, structured_output flag; v2.1.1 points at migration guide
Model Context Protocol
v2.1.0 on Aug 24: `Client` accepts `StdioServerParameters` directly (no manual stdio wiring). Prompt messages accept `Image` and `Audio`; `Message`/`UserMessage`/`AssistantMessage` exported from `mcp.server.mcpserver`. 4 MiB request-body limit now applies to SSE transport and OAuth endpoints too. Handler exceptions are now logged once at ERROR and clients see `Error executing tool <name>` instead of exception text. Content-block return annotations no longer advertise `outputSchema` unless `structured_output=True`. TypedDict tool results: `NotRequired` keys omitted instead of serialized as `null`. The 2026-07-28 notifications spec change (e.g. `notifications/cancelled`) is honored: clients get a 202 acknowledgement instead of a 400 rejection. `mcp install` reads and preserves non-ASCII Claude Desktop config on Windows. v2.1.1 (Aug 25) is a one-line follow-up: imports in `mcp.server.fastmcp` are redirected at the migration guide (the v2.x line is moving the FastMCP path). v1.29.1 (Aug 24) pairs with v2.1.0: completes the FastMCP Settings model at import time, applies the request-body limit to SSE/OAuth, gives recursive tool return types an object-rooted output schema.
Why it matters
v2.1.0 is the first release after Anthropic's Files + Skills GA push and adds three things that line up with that direction: prompt messages accept image/audio content; structured output is opt-in per-tool via `structured_output=True`; the 4 MiB body limit is now consistent across JSON-RPC, SSE, and OAuth endpoints — together they raise the ceiling for richer MCP tool payloads. The v2.1.1 redirect into a migration guide signals the FastMCP import path is moving; users importing `mcp.server.fastmcp` directly should expect breakage.
Importance: 3/5
MCP Python SDK major (v2.1) with new content types and structured_output flag