# MCP Streamable HTTP transport SSE endpoint deprecated 2025 specification

Status: search-observed
Product: MCP
Last verified: 2026-06-25
Canonical HTML: https://gitdocs.org/fix/mcp-streamable-http-transport-sse-endpoint-deprecated-2025-specification
Machine JSON: https://gitdocs.org/api/fixes/mcp-streamable-http-transport-sse-endpoint-deprecated-2025-specification.json

## Exact Symptom

See the observed Codex queries below.

## Diagnosis

Local client/server code can each be valid for an earlier protocol revision; only the negotiated current spec defines transport, session, and authorization behavior.

## Fix

```
Verifier checks current transport framing, session lifecycle, auth flow, and backwards compatibility where specified.
```

## Avoid

- Changing local code without checking the current external contract.
- Retrying the same install, build, or API call with no version/source change.
- Applying a broad unsafe bypass when a narrow compatibility fix is available.

## Observed Codex Queries

- MCP Streamable HTTP transport SSE endpoint deprecated 2025 specification
- https://modelcontextprotocol.io/specification/2025-03-26/basic/transports
- https://modelcontextprotocol.io/specification/2025-06-18/basic/transports

## Sources

- MCP 2025-03-26 key changes: https://modelcontextprotocol.io/specification/2025-03-26/changelog
- Official reference opened by Codex: https://modelcontextprotocol.io/specification/2025-03-26/basic/transports
- Official reference opened by Codex: https://modelcontextprotocol.io/specification/2025-06-18/basic/transports