WatchOS 3 will bring a number of big changes to the watch, but it also adds a bunch of stuff for developers to take advantage of. Developers will be able to integrate Apple Pay within apps on the Watch, have fitness apps run in the background and more. Apps will be able to track heart rates, gyroscope and all-day accelerometers in real-time.

Apple has also announced SpriteKit and SceneKit for developers, and opened up the Crown and Touch events support. The Apple Watch will gain Game Center, CloudKit and more integrations as well. Interested developers will be able to grab the preview release today, with a public release coming this fall.

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