API releases
Every release of the REST API and the MCP server is in the API release notes, newest first, with the fields, errors and limits each one changed. The same releases are lines in the product changelog, tagged Developers, so one feed carries both.
The version the API answers today is in the OpenAPI document under info.version, and every MCP server answers the same version in its server info.
Brand terms
The terms a brand accepts when it approves a plan are versioned. Each version keeps its own address, and a plan stays under the version it was signed under. The history is in brand terms changes.
Product changelog
The product changelog lists what changed in the app and the site each week, tagged new, improved or fixed, with the build each change shipped in. Follow it by RSS or JSON feed.