How do you run a release train for many apps: cadence, branch cuts, ownership, go/no-go criteria, hotfix lanes and shared SDK versions?

A release train ships on a fixed schedule (for example every two weeks) whatever is ready, instead of waiting for features: what is not ready waits for the next train, so each release is small, the process is practised and nothing is held hostage. The mechanics: on a fixed day the release branch is cut from main; a stabilisation window allows only fixes (cherry-picked from main, reviewed and tracked); release candidates build in CI and go to TestFlight; a go/no-go meeting or automated gate checks agreed criteria; the build is submitted, released with a phased rollout and watched, and the branch is closed. A release captain (rotating) owns the calendar, the checklist, communication and the decision to halt. Features reach users through flags (see the flags question), so merging code does not mean exposing it, and a risky feature can slip a train without moving the schedule.

With many apps sharing code, add structure. Decide whether apps ride one train (simple, consistent, but one app’s problem can delay all) or independent trains with a compatibility policy. Version shared SDKs and modules semantically (Q360, Q362), publish them to an internal registry, and keep a compatibility matrix of which app versions use which SDK versions, so an incident can be traced to a module change. Define gates that every app meets: crash-free sessions, hang and launch budgets (Q432), accessibility and test health (Q453, Q477), size limits and a clean security scan, measured automatically. Keep a hotfix lane with a shorter checklist, and a freeze policy for peak periods. Measure the process, not only the product: lead time from merge to users, frequency, the share of releases needing a hotfix and time to restore after a bad release. Publish the calendar, the rules for getting a change in, and a blameless review after every incident. At the staff level your job is to make the right thing the default, so releases are uneventful and nobody dreads them.