MCP publishes its Skills extension, SDKs haven't caught up

The Model Context Protocol's Skills extension is now marked Final under proposal SEP-2640, and the protocol's spec docs caught up with that status on September 18 in PR #3372. The extension itself lives in a separate repo, modelcontextprotocol/ext-skills, and works by distributing skills through MCP's existing Resources primitive rather than adding a new one.

That's a real design choice worth sitting with for a second. Skills don't get their own protocol surface. A server exposes them the same way it exposes any other resource, and a client that already speaks Resources gets skills discovery close to free, in theory.

In practice, nobody's client speaks it yet. The PR is explicit that finalizing the spec and shipping SDK support are two different jobs, and the second one hasn't happened. Implementation PRs for the Go, Python, TypeScript and C# SDKs are all still open. A server author can point at the finished spec, but a client built on any of the four official SDKs can't consume a Skills-exposing server until its language's SDK PR merges and ships.

That gap matters because "Final" reads as "stable" to anyone skimming the spec status, and stability at the protocol layer doesn't buy you a working client. If you're designing against MCP now, treat the Resources-based approach as the target shape, not something you can wire up before those four PRs close. The thing to watch is which SDK merges first. Whichever language gets support becomes the reference implementation everyone else's client library gets compared against, and that usually sets defaults the other three end up copying.