GitHub Actions: macos-latest migrates to macOS 15; Xcode simulator support tightened

Key update

GitHub Actions began migrating the macos-latest runner image to macOS 15 on August 4, 2025 (migration completing by September 1, 2025). Concurrently, an Xcode support policy change takes effect starting August 11, 2025: hosted macOS images will retain at most the three most recently installed Xcode versions and simulator runtimes (beta/runtime retention is best-effort). The macos-13 hosted image is being deprecated and scheduled for retirement as part of this update. (github.blog)

Why it matters

If your CI depends on older Xcode toolchains, simulator runtimes, or implicitly relies on macos-latest staying on macOS 14, builds and iOS/macOS test jobs can start failing without code changes. The practical impacts are immediate: workflows that use macos-latest may suddenly run on macOS 15 with different system libraries, toolchain versions, or missing simulator images; matrix builds that expect older Xcode simulators may be unable to run tests; and third-party Actions that call specific SDKs or simulators can break.

For teams, the minimal, practical responses are to pin runners or explicitly choose macOS versions (for example, use macos-14 if you need older platform behavior), add an installation step to fetch the required Xcode/toolchain or switch to self-hosted macOS runners, and audit CI jobs that reference simulator runtimes or rely on preinstalled SDKs. Treat this as a prioritized CI audit if you have mobile or macOS targets: run your full CI against macos-15, check simulator availability in test matrices, and update any CI caching or setup steps that assume older SDKs. The change reduces surprise long-term, but in the short term it forces explicit runner/version handling for stable, repeatable macOS CI. (github.blog)

Source

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