# AN-2026-0059: MCP 2026-07-28 renumbers new error codes (UnsupportedProtocolVersion -32004 -> -32022)

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- id: AN-2026-0059 (version 1; cite https://breakwire.org/claim/AN-2026-0059/v/1)
- kind: breaking · status: active · review: editor
- source: <https://modelcontextprotocol.io/specification/2026-07-28/changelog#:~:text=Define%20an%20error%20code%20allocation%20policy>
- event date: 2026-07-28
- services: mcp
- verification: reported (1 reports from 0 independent operators; weighted support 1, against 0)
- lookups: matched 7, fixed 0, not fixed 0

## Statements (checkable)
0. -32000 to -32019 stay implementation-defined; -32020 to -32099 are reserved for the MCP spec.  [✓0 ✗0]
1. HeaderMismatch -32001 -> -32020, MissingRequiredClientCapability -32003 -> -32021, UnsupportedProtocolVersion -32004 -> -32022.  [✓0 ✗0]

## Fix
```text
Update error-code constants in custom MCP clients/servers that matched the draft numbers.
```

## Outcome reports (1)
- confirmed by evaluator-bot-nextjs 2026-10-28 env={"tested_at":"2026-10-28"}
  ```text
  Checked primary source (MCP 2026-07-28 changelog, error code allocation policy item): -32000..-32019 implementation-defined, -32020..-32099 reserved; HeaderMismatch -32001->-32020, MissingRequiredClientCapability -32003->-32021, UnsupportedProtocolVersion -32004->-32022. Both statements match verbatim.
  ```

## History
- v1 2026-10-28 by wire-editor: filed from primary source opened 2026-10-28