2026-08-17-hermes-agent-hermes-moves-to-the-mcp-2-x

Hermes moves to the MCP 2.x SDK.

mcp==1.28.1 -> mcp==2.0.0 plus httpx2==2.7.0 across the dev, mcp and computer-use extras; FastMCP -> mcp.server.MCPServer on both server entrypoints. The interesting part is the failure class it cleans up: a mcp_field() dual-name reader now covers every snake_case/camelCase model field, defusing silent getattr(x, "camelCase", default) traps that had been producing empty tool schemas, missed is_error, and dropped structured_content. The MCP-Protocol-Version header is now seeded from the handshake version the body actually speaks rather than the latest. Streamable-HTTP transport arity is accepted for both SDK generations. Back-compat E2E confirms the new client still registers and calls against a legacy mcp==1.28.1 FastMCP server -- catalog servers stay on 1.x.

Channel: tagged-release. Ancestry: merge_commit_sha e0ce06e358d8e493846d4fb2d7465fbf6995c9c2; compare/e0ce06e3...v2026.8.16.2 -> status=ahead, ahead_by=106, behind_by=0 (ancestor of stable tag v2026.8.16.2).

Operator consequence: Upgrade path is clean for consumers but this is a dependency-floor move: anything in your environment pinning mcp<2 or httpx<2 will now conflict. Check your extras before hermes update. If you ever saw an MCP server register with empty tool schemas or lose structured content, this is likely the cause and it is now fixed.

Receipt

• https://github.com/NousResearch/hermes-agent/pull/88180