MCP 2026-07-28 drops initialize: does Sume answer server/discover?

No. Sume's hosted MCP server does not answer server/discover today. The code on origin/main, read on 2026-10-04, handles four JSON-RPC methods (initialize, ping, tools/list and tools/call), and any other method returns error -32601, method not found. The 2026-07-28 revision of the Model Context Protocol removes initialize and requires servers to implement server/discover, so a client that speaks only that revision cannot complete a handshake with Sume yet.

That matters less than it sounds, because Sume also speaks the older revisions that clients still send.

What changed in the spec?

The 2026-07-28 changelog removes sessions and the Mcp-Session-Id header (SEP-2567) and makes the protocol stateless. initialize goes away, server/discover takes its place and servers must implement it (SEP-2575). The same changelog removes ping, logging/setLevel and roots/list_changed, moves tasks to an extension, and adds Mcp-Method and Mcp-Name request headers.

Which revisions does Sume list?

What should I do today?

Point clients at https://mcp.sume.com/mcp and let them negotiate to 2025-11-25, which is what Sume returns as its default. If your client or gateway pins 2026-07-28 only, expect the discovery call to fail with -32601 and use a client that can fall back, or keep the pin off until Sume lists the new revision. Sume's own server code is the source of truth here, not this post, so check the live initialize response from your session.

The AgentCore Gateway page lists 2026-07-28 among its supported protocol versions, which shows why a stateless-only client is plausible in a gateway. Its session-id guidance applies to 2025-11-25 and earlier, while 2026-07-28 is stateless.

Does the stateless change affect my tool calls?

Sume's tool surface does not depend on a session for the calls that matter: tools/list returns the tools your credential can see, and tools/call runs one. Long work goes through jobs, where you create, then jobs_wait, then jobs_result. The MCP quickstart and the MCP overview walk through the flow with the current revisions.

How can I check what my client sends?

Capture the first request your client makes to https://mcp.sume.com/mcp. If it is initialize with a 2025 protocol version, you are on a supported path. If it is server/discover, expect -32601 until Sume lists the new revision. The answer to "will it work" depends on the client's fallback behavior, which the specification changelog does not decide for you, so test with the exact build you plan to ship and keep an API-key fallback ready.