watchOS 4 SDK Release Notes



watchOS 4 SDK provides support for developing watchOS apps. It is packaged with a complete set of Xcode tools, compilers, and frameworks for creating apps for watchOS. These tools include the Xcode IDE and the Instruments analysis tool, among many others.

With this software you can develop apps for Apple Watch running watchOS 4. You can also test your apps using the included watchOS Simulator, which supports watchOS 4. watchOS 4 SDK requires a Mac computer running macOS Sierra 10.12.6 or later.

This version of watchOS is intended for installation only on devices registered with the Apple Developer Program. Attempting to install this version of watchOS in an unauthorized manner could put your device in an unusable state.

Tools and Developer Resources

You obtain Xcode 9 from the Mac App Store. It is a free download that installs directly into the Applications folder. By default, Xcode downloads developer documentation in the background for offline reading; it also automatically downloads documentation updates. This behavior can be changed after installation using the Downloads preferences pane.

The Apple Developer Program provides access to the App Store, Mac App Store, and Apple TV App Store, additional support and documentation, and signing resources for testing and deployment on Apple TV, Apple Watch, iPad, iPhone, and iPod touch devices. For more information, visit the Apple Developer Program website.

Apple provides the following web resources to support development in watchOS:

Bug Reporting

For issues not mentioned in Notes and Known Issues, please file bugs through the Apple Developer website

When filing a bug, please include the full version number in the bug title and in the description. To find the version number, on iPhone open Apple Watch and navigate to My Watch > General > About. The version number is next to Version and looks like 4.0 (15Rxxxxx).

Additionally, you may discuss these issues and watchOS 4 SDK in the Apple Developer Forums at

Release Notes Updates

watchOS Release Notes is sometimes updated after a release is distributed. You can check for the most up-to-date version of watchOS Release Notes at the Apple Developer website by checking

Revision: watchOS400 - WRN1

Notes and Known Issues

The following items relate to using watchOS 4 SDK to develop code.


Known Issues

  • CloudKit doesn't support unsigned long long values with the high-order bit set. (30567424)

  • Applications that use CKModifyRecordsOperation should specify an appropriate value for CKModifyRecordsOperation.isAtomic. If your client is compiled against watchOS 4, operations enqueued against the default CKRecordZone have new behavior because atomic is true by default. If the operation hits a "preflight" failure (most commonly, a network issue uploading a CKAsset, or a malformed CKRecord), the entire operation is canceled. (30838858)


Known Issues

  • CoreBluetooth is not supported on original Apple Watch or Apple Watch Series 1. (34049299)


Known Issues

  • To track location in the background while a user is in a workout session, add UIBackgroundModes/location in the Info.plist file. (29483437)


Known Issues

  • Automatic display of attachments in default WatchKit Notification interfaces do not work. (31589086)


Known Issues

  • Crashlogs may take a few minutes to sync and be visible in Xcode. (31156191)