# Versioning

Platform API version `2026-09` is published under stable `/v1` resource grammar. Additive compatible fields may appear without a route-version change. Breaking wire or semantic changes require an explicit version transition and migration account.

Published Business App Engine App Versions are immutable authorities for the Cases, Runs, Effects, and Receipts that used them. Deploying a later App Version never rewrites the application definition attached to historical work.