Valve has announced the Steam client now includes full support for Sony’s DualShock 4 controller. You’ll be able to customize the controller’s buttons, including the trackpad and gyroscope, to map them to various Steam functions. PS4 controllers can also utilize the same APIs that are available for Steam controllers.

PS4 controllers will have access to the same sort of customization/configuration support as Steam Controllers, including native API support. PS4 Controllers using this system can map the trackpad, gyro, buttons, etc. to keyboard, mouse, or x-input outputs and can make use of action sets, touch menus, radial menus, and so forth.
– Valve

Other controller-related and entirely unrelated changes are included in this update. You can view the full list of Steam client changes here.

Valve announced in October that it would be expanding its controller support in Steam.

via Steam Now Fully Supports PS4 Controller | NextPowerUp