A dated count finds five MCP protocol revisions in use at once
An independent count published on 2 October 2026 sent an initialize request to 186 remote MCP endpoints taken from the official registry, on 1 and 2 October. Of the 72 endpoints that returned a protocol version, 7 (9.7%) negotiated the newest revision, 2026-07-28, and the rest answered with one of four older revisions; 86 were behind a sign-in. The author notes that the endpoints are a slice of the registry by hostname, not a random sample.
Why it matters
Clients and servers will meet on different revisions for some time, so a server that still negotiates the older revisions cleanly can be reached by more agents. Owners can check which revision their server answers with before they rely on the new one.