Claude Skills API Is GA: Ship a Versioned Skill

On August 19, 2026 Anthropic flipped Agent Skills and the Skills API (/v1/skills) to generally available on the Claude API. The skills-2025-10-02 beta header is gone. The Files API went GA in the same release note, which matters because those two features are how a Skill gets its work back out of the sandbox.

The interesting part is not the header removal. It is that Skills now have a stable versioning story, and almost everyone shipping them is using it wrong. The default "latest" resolution means anyone in your workspace can change what your production agent runs by uploading a new version. Custom Skills are workspace-scoped, not key-scoped, so "anyone" is broader than most teams assume.