Ruby SDK 1.5.0 makes the client answer server pings with the required empty result

The official Ruby SDK released v1.5.0 on 2026-09-05. Per the release notes, it "makes the client answer a server's ping with the empty result the specification requires." Earlier clients replied with Method not found over Streamable HTTP and stayed silent over stdio, so "a server that checks liveness dropped their long-lived sessions."

Two OAuth changes ship alongside the fix. authorization_request_validator lets the embedding application refuse an authorization request (#539). Stored tokens are now refreshed only against the authorization server that issued them: when the server named for a session differs, the client reauthorizes instead of refreshing, and the validator sees the newly named server; tokens stored by earlier releases carry no issuer and keep refreshing as before. v1.5.1 followed on 2026-09-09, fixing HTTP client compatibility with Faraday and json 3.0.

The SDK's proposed promotion from Tier 2 to Tier 1 has not progressed. PR #3248 in the spec repo, which proposes the promotion, was still open as of 2026-09-15, with no activity since its last update on 2026-08-23. The previous release, v1.4.0, repaired the subscriptions/listen stream's delivery ordering.