Deprecate roots, sampling, and logging per SEP-2577#406
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Warn when Roots, Sampling, or Logging APIs are used with MCP protocol version 2026-07-28, while leaving the latest stable default at 2025-11-25. Add a shared protocol deprecation helper, YARD deprecation notes, and regression tests covering warnings for 2026-07-28 and no warnings for older protocol versions. Closes modelcontextprotocol#390
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@koic Happy to push this through or were you thinking of doing the deprecation later? |
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I'd lean toward doing the deprecation later rather than merging the full behavior change now. This SEP introduces a behavioral switch tied to protocol versioning, and I think that design makes sense because it preserves compatibility with existing protocol versions. However, the 2026-07-28 specification hasn't actually been released yet, and it doesn't appear to have been added to Given that, I'd prefer to wait until the 2026-07-28 release is closer before enabling the deprecation behavior. In the meantime, it might be reasonable to land the advisory annotations on their own. |
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@koic Sounds good! I can split out the advisory. |
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Split the advisory YARD @deprecated annotations out of modelcontextprotocol#406 so the documentation can land ahead of the 2026-07-28 protocol release. Per maintainer feedback, this drops the protocol-version-gated runtime Kernel.warn behavior and the new 2026-07-28 supported protocol version, leaving only the @deprecated notes for the Roots, Sampling, and Logging APIs deprecated by SEP-2577. Refs modelcontextprotocol#390 Co-authored-by: 🦞 Qlaw <noreply@qlaw.quick.shopify.io>
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Split the advisory annotations out into #429 so they can land independently of the protocol-version behavior change. I'll keep this PR open for the |
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## Motivation and Context The MCP specification defines `sampling/createMessage` as a server-to-client request that lets a server ask the client to generate an LLM completion, so the server can leverage the client's model access without its own API keys. The Ruby SDK already supports the server side (sending the request) and, on the client side, the generic server-to-client request infrastructure introduced for elicitation (the standalone GET SSE listening stream and `on_server_request` dispatch). This adds the client-side `sampling/createMessage` handler on top of that infrastructure. ## Changes - Add `MCP::Client#on_sampling`, a thin wrapper that registers a `sampling/createMessage` handler via `transport.on_server_request`, mirroring `on_elicitation`. The handler receives the request params and returns a `CreateMessageResult`-shaped Hash sent back as the JSON-RPC result. - Document client-side sampling in the README, including the `sampling` (and `sampling.tools`) capability declaration and the human-in-the-loop guidance from the specification. ## How Has This Been Tested? - Unit tests for `on_sampling` covering handler registration on the transport and the error raised when the transport does not support server-to-client requests. - An HTTP transport test that dispatches a `sampling/createMessage` server request delivered on the SSE stream and returns a `CreateMessageResult`. ## Deprecation Note SEP-2577 deprecates sampling (along with roots and logging) starting with protocol version `2026-07-28`. The deprecation warnings are added in #406. Sampling remains fully supported under the current `2025-11-25` protocol version and stays available throughout the spec's deprecation window, so the client side is implemented here for parity with the server side and with the Python and TypeScript SDKs. `MCP::Client#on_sampling` carries the same `@deprecated` annotation as the server-side senders annotated in #429, tailored to the receiving side: the handler exists to interoperate with servers that still send sampling requests during the deprecation window. The README section carries the same note. Ref: https://modelcontextprotocol.io/specification/2025-11-25/client/sampling
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TL;DR
Deprecate MCP Roots, Sampling, and Logging only when protocol version
2026-07-28is negotiated or explicitly configured.Context
SEP-2577 deprecates Roots, Sampling, and Logging in the
2026-07-28protocol version.Closes #390
Changes
2026-07-28as an explicitly supported stable protocol version while keepingLATEST_STABLE_PROTOCOL_VERSIONat2025-11-25.Kernel.warnmessages only for2026-07-28.2026-07-28.@deprecatednotes and regression tests for both warning and no-warning behavior.Testing
GEM_HOME="$PWD/.gem-test" GEM_PATH="$PWD/.gem-test:/nix/store/jh918yiwd5cs4pjg005ac32m2q7ckw3l-ruby-4.0.5/lib/ruby/gems/4.0.0" bundle exec rake testGEM_HOME="$PWD/.gem-test" GEM_PATH="$PWD/.gem-test:/nix/store/jh918yiwd5cs4pjg005ac32m2q7ckw3l-ruby-4.0.5/lib/ruby/gems/4.0.0" bundle exec rake rubocopgit diff --check