Streamable HTTP
Also called: Streamable HTTP transport
The current HTTP transport for MCP, using a single endpoint that can optionally upgrade to a stream, replacing the older HTTP+SSE design.
Introduced in the 2025-03-26 protocol revision, Streamable HTTP collapses the earlier two-endpoint (POST + SSE) design into one HTTP endpoint. The server may answer a request with a plain JSON response or, when it needs to push multiple messages, with a Server-Sent Events stream. It also tightened guidance on session handling and origin validation.
Why it matters
The transition period matters for anyone surveying exposed infrastructure: both the legacy HTTP+SSE shape and the newer Streamable HTTP shape are observable on the internet right now, and they fingerprint differently. The revision also added security guidance (validate the Origin header, bind local servers to loopback) precisely because early deployments were getting it wrong.
Exposure map
Live counts of instances showing this pattern will appear here once the exposure map is collecting data.