Agents SDK mcp.Client mode auto against Sume's MCP server
With MCP Python SDK v2, the Agents SDK probes the newest protocol and falls back to initialize. Sume's hosted server still serves initialize with 2025-11-25.
An Agents SDK connection using mcp.Client(mode="auto") probes for the newest protocol and falls back to the legacy initialize handshake for older servers. Sume's hosted MCP server is such a server: it serves initialize and negotiates among 2025-03-26, 2025-06-18 and 2025-11-25.
Vendor facts are from the Agents SDK release notes; Sume facts from the MCP server source and the MCP quickstart, read 2026-10-01. The raw handshake is covered in the discover RPC post.
What does the Agents SDK release say?
Local MCP connections now support MCP Python SDK v2 while keeping v1 compatibility through mcp>=1.19.0,<3. With v2 installed, stdio, SSE and Streamable HTTP connections use mcp.Client(mode="auto"). Custom httpx.Auth objects or httpx.AsyncClient factories must move to httpx2, or you pin mcp<2.
What does Sume negotiate?
| Behavior | Value |
|---|---|
| Supported versions | 2025-03-26, 2025-06-18, 2025-11-25 |
initialize server name | sume-remote-mcp |
| Version header not in the list | 400, "Unsupported MCP protocol version." |
| Endpoint | https://mcp.sume.com/mcp |
How do I confirm the connection works?
After connecting, list tools and call mcp_health, which the quickstart describes as confirming endpoint, auth source and safety posture. If tools are missing, check the auth header first, then the negotiated version.
Do I need to pin mcp below 2?
Not for Sume's protocol versions on the evidence above; the fallback exists for this case. You may still need httpx2 migration for custom auth, which is an Agents SDK matter, not a Sume one.
Sources
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