Source note · Model Context Protocol transports compared
Under MCP revision 2026-07-28, a client that wants to support older HTTP+SSE servers POSTs a request to the server URL and, if it fails with 400, 404 or 405 and the response body is not a recognized modern JSON-RPC error, issues a GET expecting an SSE stream whose first event is an endpoint event, after which it uses the old transport.
Checked 2026-09-30
- Vendor
- Model Context Protocol project
- Product
- MCP specification
- Subsystem
- backward compatibility
- Deployment
- remote-http
- Region
- not restricted
- Release range
- MCP revision 2026-07-28
- Checked
- 2026-09-30
Sources
- Model Context Protocol specification 2026-07-28, Streamable HTTP — Model Context Protocol project · tier 1 standards and regulators · section Backward Compatibility, subsection HTTP+SSE Transport (2024-11-05), Clients list
Cite this note
APA
WarmTransfer. (2026, September 30). Model Context Protocol transports compared: source note mcp-transport-differences-http-sse-fallback. WarmTransfer. https://warmtransfer.net/knowledge/claims/mcp-transport-differences-http-sse-fallback
BibTeX
@misc{warmtransfer-claim-mcp-transport-differences-http-sse-fallback,
title = {Model Context Protocol transports compared: source note mcp-transport-differences-http-sse-fallback},
author = {{WarmTransfer}},
year = {2026},
url = {https://warmtransfer.net/knowledge/claims/mcp-transport-differences-http-sse-fallback},
note = {Source note mcp-transport-differences-http-sse-fallback, checked 2026-09-30}
}