Apple released build14D98g of OS X Yosemite 10.10.3 to developers on Thursday. The new seed includes the Photos for OS X app, and new APIs to support the new Force Touch trackpad found on the new 12-inch MacBook and 13-inch MacBook Pro with Retina Display.
The new build (14D98g) is available for download by developers via download from the Mac Developer Center, and via the “Update” tab in the Mac App Store.
From the OS X 10.10.3 Seed Notes:
This beta of OS X 10.10.3 contains new developer APIs that work with the Force Touch trackpad in the new MacBook Pro (Retina, 13-inch, Early 2015) to allow a new level of interactivity and control within your apps.
Force click. Apps can have any button, control, or region on the screen respond to a press of stronger pressure. This Force click can provide a shortcut to additional functionality within the app.
Accelerators. Pressure sensitivity in the trackpad enables apps to give users greater control. For instance the fast-forward button in media playback can speed up as pressure increases.
Pressure sensitivity. Drawing and other creative apps can take advantage of the pressure-sensing capabilities of the trackpad to make lines thicker or give the brush a changing style.
Drag and Drop. Apps can add the springLoaded property to their controls so they can react to a Force click gesture while in the middle of performing a drag, for instance to immediately open a new target for the drop.
Alongside the new beta seed of OS X 10.10.3, Apple also released seeds of OS X Server 4.1 Developer Preview (build 14S1062i), and Xcode 6.3 beta 3 with Swift 1.2 (build 6D543q).