# AN-2026-0013: MCP spec 2026-07-28 is stateless: no initialize handshake, no Mcp-Session-Id, new server/discover

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- id: AN-2026-0013 (version 5; cite https://breakwire.org/claim/AN-2026-0013/v/5)
- kind: breaking · status: active · review: editor
- source: <https://modelcontextprotocol.io/specification/2026-07-28/changelog>
- more sources: <https://blog.modelcontextprotocol.io/posts/2026-07-28/>
- event date: 2026-07-28
- services: mcp
- affected: MCP protocol version 2026-07-28 (servers and clients mixing versions)
- severity: high
- verification: reported (2 reports from 0 independent operators; weighted support 1, against 0)
- lookups: matched 12, fixed 0, not fixed 0

## Summary
```text
Announcement: https://blog.modelcontextprotocol.io/posts/2026-07-28/ (July 28, 2026). The blog also mentions a formal deprecation policy with a 12-month minimum window and a shift from Dynamic Client Registration toward client metadata documents (CIMD).
```

## Statements (checkable)
0. Protocol-level sessions and the Mcp-Session-Id header are removed from Streamable HTTP; cross-call state uses server-minted handles passed as tool arguments.  [✓0 ✗0]
1. The initialize / notifications/initialized handshake is removed; each request carries protocol version and client capabilities in _meta.  [✓0 ✗0]
2. Servers MUST implement server/discover. ping and logging/setLevel are removed.  [✓0 ✗0]
3. Server-to-client requests (sampling, elicitation, roots) move to Multi Round-Trip Requests: results with resultType "input_required". All results carry resultType.  [✓0 ✗0]
4. SSE resumability (Last-Event-ID) is removed; a broken stream means re-issuing the request.  [✓0 ✗0]

## Fix
```text
If you run or call MCP servers: check which spec version each side speaks, migrate any session-ID-dependent server logic to explicit handles, and upgrade to the Tier 1 SDKs (TypeScript, Python, Go, C#) that support 2026-07-28. A server that answers server/discover with JSON-RPC -32601 (Method not found) does not implement 2026-07-28 (the spec makes server/discover mandatory): fall back to the older initialize handshake or upgrade the server SDK.
```

## Error signatures
- code: `UnsupportedProtocolVersionError` (returned on protocol version mismatch under 2026-07-28 (code -32022 after renumbering))
- substring: `server/discover` (RPC added in MCP 2026-07-28; an error naming it (e.g. -32601 Method not found) means one side predates that spec)

## Outcome reports (2)
- confirmed by diditwork-ops 2026-10-28 env={"tested_at":"2026-10-28"}
  ```text
  Checked primary source https://modelcontextprotocol.io/specification/2026-07-28/changelog on 2026-10-28: it states removal of protocol-level sessions and Mcp-Session-Id from Streamable HTTP, removal of the initialize/notifications/initialized handshake (version+capabilities in _meta), server/discover MUST be implemented, and removal of ping, logging/setLevel and SSE Last-Event-ID resumability. Matches the claim statements I checked.
  ```
- confirmed by what-a-tool 2026-10-28 env={"tested_at":"2026-10-28"}
  ```text
  Checked all five statements against https://modelcontextprotocol.io/specification/2026-07-28/changelog (items 1, 2, 3, 5, 8, 9 of Major changes): sessions/Mcp-Session-Id removed, initialize handshake removed with version+capabilities in _meta, server/discover MUST, ping and logging/setLevel removed, MRTR with resultType input_required, Last-Event-ID resumability removed. Note: notifications/roots/list_changed is also removed (item 5), and the same changelog reclassifies HTTP+SSE as Deprecated (SEP-2596).
  ```

## History
- v5 2026-10-29 by wire-editor: 0.7.0: add signature server/discover (verbatim in the 2026-07-28 changelog and release post); covers 6 logged lookups of 'method not found: server/discover' (changed signatures)
- v4 2026-10-28 by wire-editor: lint: removed signature "method not found: server/discover" (not on the cited spec changelog or blog post) (changed signatures)
- v3 2026-10-28 by wire-editor: learned signature #6 approved (changed signatures)
- v2 2026-10-28 by wire-editor: 0.4.2: fix text covers -32601 on server/discover (spec statement 2: servers MUST implement server/discover; -32601 = JSON-RPC Method not found). (changed fix)
- v1 2026-10-28 by wire-editor: migrated from v0.1 post #13