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FastMCP 4.0 first alpha released (announcement dated 2026-07-22) and built on MCP…

2026-07-22 · 11:35 UTC ·@jlowin ·0 min read

Brief

FastMCP 4.0’s first alpha (announced 2026-07-22) is based on the MCP SDK v2 and prepared for the 2026-07-28 protocol spec. The build is a compatibility/upgrade test release with a limited set of breaking changes—primarily existing deprecations and a few SDK-driven changes—and the author requests server testing feedback, expecting most servers to upgrade unchanged.

Why it matters

FastMCP 4.0 first alpha released (announcement dated 2026-07-22) and built on MCP SDK v2.

Key details

  • Release targets the new protocol spec dated 2026-07-28 and is intended solely for compatibility and upgrade testing.
  • Alpha contains a small number of breaking changes (mostly previously announced deprecations, plus a few to match SDK v2); author asks operators to test servers and report results, believing the vast majority will upgrade without changes.
Source evidence

The first alpha of FastMCP 4.0 is out.

FastMCP 4 is built on the MCP SDK v2 and designed for the new 2026-07-28 protocol spec. The alpha release is solely for compatibility and upgrade testing. It includes a small number of breaking changes (mostly existing deprecations, but a few to comply with the SDK's many breaking changes).

I'd appreciate it if you'd test your servers and let me know what works!

I believe that the vast majority of FastMCP servers should be able to upgrade without changes.