Claude Code Bedrock/Vertex MCP 2026-07-28 default vs Sume
Claude Code on Bedrock, Vertex and Foundry now negotiates MCP 2026-07-28 by default. The opt-out env vars, and the versions the Sume server accepts.
Since Claude Code 2.1.274, Bedrock, Vertex, Foundry and telemetry-disabled installs use the v2 MCP client and 2026-07-28 negotiation by default. The opt-outs are MCP_SDK_GENERATION=v1 or MCP_PROTOCOL_NEGOTIATION=legacy. The Sume MCP server's default protocol version in code is 2025-11-25, so check the connection rather than assuming either side.
Vendor facts are from the Claude Code changelog; Sume facts are from the MCP server code, read 2026-10-01. The connect command is in the MCP quickstart.
What exactly changed in 2.1.274?
The September 17, 2026 entry says these installs now use the v2 MCP client and MCP 2026-07-28 negotiation with direct HTTP servers, as other installs already do. It names two opt-outs: MCP_SDK_GENERATION=v1 and MCP_PROTOCOL_NEGOTIATION=legacy.
Which protocol versions does the Sume server use?
In packages/mcp-server/src/mcp.ts the default is MCP_PROTOCOL_VERSION = "2025-11-25", and the supported list also contains 2025-03-26 and 2025-06-18. When a client requests a version in that list the server answers with it; otherwise it answers with 2025-11-25. The initialize response reports serverInfo name sume-remote-mcp, version 0.4.0.
| Version string | Role in the server |
|---|---|
| 2025-11-25 | Default, returned for unknown requests |
| 2025-06-18 | Supported |
| 2025-03-26 | Supported |
| 2026-07-28 | Not in the supported list in this code |
Do I need the opt-out for Sume?
I can not tell from these sources how Claude Code behaves when the server only offers 2025-11-25, so test it. Connect with claude mcp add --transport http sume https://mcp.sume.com/mcp and call mcp_health. If the connection fails on a cloud-provider install, set MCP_PROTOCOL_NEGOTIATION=legacy and retry. A server-side rejection is described in unsupported protocol version 400.
Sources
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