Stay on Tahoe 26.7.1. Hold macOS 27.

Apple's Xcode page also lists Xcode 27.1 RC and 27.2 beta 2, both needing Tahoe 26.6 or later. I found no macOS releases Oct 1 to 9, no Rapid Security Responses or Background Security Improvements, and no pulled updates.

Intel and Sonoma: macOS 27 and Xcode 27 don't run on Intel Macs. Sonoma got no updates this cycle. Move any stragglers to Sequoia 15.8.1 or Tahoe 26.7.1.

• Xcode 26 on macOS 27 shows "not compatible with this version of macOS".
• The iOS 27 SDK requires the UIKit scene lifecycle. Apps without it build, then fail at launch: UIScene life cycle is required for apps built with this SDK. Apps built with older SDKs still run on iOS 27.
• Deployment target: the minimum is iOS 15. Targets of 13.x or 14.x fail.
• Device debugging needs iOS 17 or later. Keep Xcode 26 for iOS 15 and 16 test devices.
• Device Hub replaces Simulator.app. Scripts that drive Simulator.app may need changes. simctl and devicectl still work.
• Address Sanitizer may fail on iOS 27 with Xcode 26.4 or older. Use 26.5 or later.
• App Store uploads currently need Xcode 26 or later with an iOS 26 SDK. An iOS 27 SDK requirement around April 2027 fits Apple's usual pattern. Unverified
• Command Line Tools: install with xcode-select --install. I found no CLT-specific issues.

Workaround on macOS 27 (emergency only): developers report that Xcode 26 runs if you launch its binary directly, and that xcodebuild works with the old toolchain selected. Apple doesn't support or document this, and some Xcode 26.3 features crashed. Community reports

/Applications/Xcode.app/Contents/MacOS/Xcode
# or build with the old toolchain:
DEVELOPER_DIR=/Applications/Xcode-26.6.app/Contents/Developer xcodebuild ...

"SDK 57" and "SDK 58" are Expo SDK versions. The patch that matters is expo@57.0.23, the first SDK 57 release with opt-in scene support. Earlier 57.x patches fixed a JavaScript-engine memory regression (57.0.9) and slow dev-mode startup (57.0.17).

Expo SDK 57 on Xcode 27:

npx expo install expo@^57.0.23
# app.json, plugins, expo-build-properties:
#   { "ios": { "enableSceneSupport": true } }
npx expo prebuild --clean

• Expo SDK 58 has been in beta since Sep 15. It's built for iOS 27, uses the scene lifecycle by default, and ships React Native 0.88 RC. The stable release follows React Native 0.88 stable.
• Expo SDK 56 and older reportedly fail to launch under Xcode 27. Secondary source
• EAS Build: the default image (latest/sdk-57) uses Xcode 26.6, and sdk-58 uses Xcode 27.0. Cloud builds don't depend on your local macOS. Pin the image.
• React Native: scene support is in 0.88, now at release candidate 2. A stable release is "scheduled for 12 October". Unverified On 0.87 or older, add a SceneDelegate yourself. Move deep-link handling to scene(_:openURLContexts:) and scene(_:continue:), then retest OAuth and push. Reanimated raised its example app's target to iOS 15.1 because Xcode 27 rejects 13.4.
• Flutter: 3.41+ auto-migrates an unmodified AppDelegate when you build. Watch for "Finished migration to UIScene lifecycle". A custom AppDelegate needs manual steps. Flutter is raising its iOS minimum to 15.

flutter upgrade
flutter build ios   # look for: Finished migration to UIScene lifecycle

Upgrading to macOS 27 doesn't reinstall Rosetta. Apps you'd set to "Open using Rosetta" now launch natively. Rosetta stays available through macOS 27. In macOS 28 it's for legacy games only.

Cursor: the agent's grep, search, read and terminal steps hang (even pwd) when the git on PATH is an Intel build, usually an old /usr/local/bin/git. Cursor staff confirmed this, and the fix is coming in 3.23. Changing the git.path setting doesn't help the agent.

# check
file "$(which git)"
# if it says x86_64, either install Rosetta:
softwareupdate --install-rosetta --agree-to-license
# or remove the old Intel git (macOS has /usr/bin/git):
sudo rm -f /usr/local/bin/git

Audit the rest of your PATH before upgrading:

file $(which -a git node python3 java ruby) 2>/dev/null | grep x86_64
ls /usr/local/bin

Installer packages that don't name an architecture default to arm64 on macOS 27. Docker amd64 images rely on Rosetta-based emulation, so test them after upgrading.

• Homebrew 7.0.0 (Sep 13): macOS 27 on Apple silicon is Tier 1 with prebuilt packages. Intel Macs have dropped to Tier 3.
• Docker Desktop: nothing macOS 27-specific in Docker's known issues. I also found no explicit support statement. Check current release notes first.
• OrbStack: the app window crashes at launch on 27.0 for some non-US number formats (issue #2596). The engine and the docker/orb command-line tools keep working. A beta-only kernel panic (#2562) was fixed before release.
• VS Code, JetBrains, git/ssh, Node, Python: I found no macOS 27 reports. Only Intel-built copies are at risk.

# OrbStack window crash workaround
open --env LC_NUMERIC=en_US.UTF-8 -a OrbStack

Tahoe VMs won't update in place. Going from 26.6.2 to 26.7 or 26.7.1 hangs on a black screen in Parallels, UTM, VirtualBuddy and VMTek. The guest is left on 26.6.2, sometimes broken. It happens on Tahoe and macOS 27.0.1 hosts. Parallels has reproduced it, and I found no fix announced. Physical Macs and macOS 27 guests are fine.

Workaround: build a fresh VM from the 26.7.1 IPSW or full installer. One user reported an overnight in-place update did eventually finish.

Parallels Desktop 27 supports macOS 27 as the host (Apple silicon only). Parallels 26 on macOS 27 is flagged "not fully optimized". An Xcode 27 beta bug that blocked macOS VM creation is fixed in Xcode 27.

• Mission Control, Spaces, Stage Manager, full screen: stutter, black or empty Spaces, missing thumbnails, and multi-display glitches. The menu bar sometimes doesn't appear in full-screen apps.
• Menu bar: menus are slow to open and Control Center lags. Menu bar managers need versions updated for 27.
• Battery and heat: widely reported, usually blamed on reindexing, background AI work or outdated apps. Some users downgraded.
• 27.0.1: reports are split, and many see no change. Apple documented only the single sign-on fix. Users report Reduce Transparency, and removing incompatible window or menu bar utilities, help.

These reports are anecdotal, though widespread.

• Update to 27.0.1 (26A434).
• Install Rosetta if you use any Intel tools: softwareupdate --install-rosetta --agree-to-license.
• Use Xcode 27 with framework versions that support the scene lifecycle. Launch Xcode 26 directly only in an emergency.
• Update Cursor to 3.23 when it ships. Use the OrbStack workaround if its window crashes.

• React Native 0.88 stable date (Oct 12): secondary source.
• April 2027 App Store iOS 27 SDK deadline: not on Apple's page yet.
• Expo SDK 56 failing under Xcode 27: secondary source.
• Running Xcode 26 directly, or xcodebuild, on macOS 27: developer reports, not Apple.
• Docker Desktop, VS Code, JetBrains on macOS 27: no statements found either way.