Post-1.0. Not for the 1.0 launch. From the WWDC 2026 review — see docs/wwdc-2026-macos-27-opportunities.md (PR #911 ), opportunity #5 .
Why (near-free wins)
Significant ViewBuilder build-time improvements in Xcode 27 — real money across 23 targets and ~350 test files.
Foundation URL parsing up to 4× faster.
Swift 6.4: @diagnose for finer-grained warning control, simplified availability syntax (anyAppleOS).
Swift Testing ↔ XCTest interop ships with this toolchain (prerequisite for the migration-policy issue).
Prerequisite for all macOS 27 SDK adoption (Foundation Models, Entity Schemas, AppKit observation, intent testing).
Plan
Validate local + CI builds on Xcode 27 beta; watch for strict-concurrency diagnostics changes (all targets are .v6 already, expect a quiet upgrade).
Check pinned-tool interactions: SwiftFormat 0.61.1 pin (mise.toml) vs. any Swift 6.4 syntax changes — do not bulk-reformat with an unpinned version (Pin/align swiftformat version — local runs reformat unrelated code (churn) #634
Verify notarization/signing pipeline (Scripts/build-and-sign.sh) against the new SDK.
Switch CI when the GM seed lands; betas via a side lane only.
https://claude.ai/code/session_01Nsiqm39oCwHkbrHytefnGM
Post-1.0. Not for the 1.0 launch. From the WWDC 2026 review — see
docs/wwdc-2026-macos-27-opportunities.md(PR #911), opportunity #5.Why (near-free wins)
@diagnosefor finer-grained warning control, simplified availability syntax (anyAppleOS).Plan
.v6already, expect a quiet upgrade).mise.toml) vs. any Swift 6.4 syntax changes — do not bulk-reformat with an unpinned version (Pin/align swiftformat version — local runs reformat unrelated code (churn) #634).Scripts/build-and-sign.sh) against the new SDK.https://claude.ai/code/session_01Nsiqm39oCwHkbrHytefnGM