Swift 6 Strict Concurrency: Production Migration Playbook

Swift 6.0's strict concurrency looks, at first glance, like an opt-in compile flag. But in reality? It's a serious refactor mandate touching every one of your classes, singletons, delegate patterns, and dependency-injection architecture.

This article walks through the 12 common pitfalls you are likely to hit when moving a large production iOS codebase to strict concurrency mode, their fixes, and the correct actor migration order. Spoiler: @MainActor is not the cure for everything.

Pro Tip: Before starting the migration, don't begin with SWIFT_STRICT_CONCURRENCY = complete — start with targeted . Targeted mode only checks Sendable; complete mode also enforces actor isolation. Starting targeted cuts your first-pass error count in half.

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