FastMCP (standalone)

The dominant Python framework for building MCP servers and clients. FastMCP 1.0 was incorporated into the official mcp package in 2024, but the standalone project continued evolving independently. Now maintained by Prefect (PrefectHQ/fastmcp), v3.0 shipped February 2026 as a major breaking rewrite. ~1M daily downloads. Powers ~70% of MCP servers across all languages. Critical: minor versions may contain breaking changes — pin aggressively.