Which macOS version first included the "Photos" app, replacing iPhoto?

OS X Yosemite was the first macOS version to include Photos, replacing iPhoto.

Apple delivered Photos for Mac in the OS X Yosemite 10.10.3 update on April 8, 2015. The app replaced both iPhoto, Apple’s longtime consumer photo manager, and Aperture, its more advanced professional photo application. Photos was designed around a simpler library experience and closer integration with iCloud Photo Library.

The transition was part of Apple’s broader effort to align photo management across Mac and iOS. Photos organized libraries using information such as dates and locations, while offering editing tools, albums, and synchronization across Apple devices. It was less focused on professional workflows than Aperture, which led some longtime users to criticize the loss of advanced features.

The answer is sometimes made confusing by the release numbering: Photos did not arrive with the original Yosemite 10.10 release in October 2014. It arrived later as part of the 10.10.3 update. El Capitan followed Yosemite, but Photos was already included by then.