10. Versioning & change policy

Additive changes — new optional fields on QAPage, new headers, new HTTP codes that only fire in previously-undocumented edge cases — may land in v3 without prior warning. Parse leniently.
Breaking changes — renaming or removing fields, type changes, tightening required constraints, default-value changes — will not land in v3. They go to v4 and run in parallel with v3 for a deprecation window of at least 90 days after announcement.
Status-code semantics are stable within a major version. A response that is 200 today will not silently become 204 or 206.
Migration notes for any future v4 will be shared with partners directly ahead of any change.