Valve continues to improve controller support in Steam. The new API version allows processing additional signals and features of modern devices. In particular, GameInput 4.0 supports lighting, touch controls, and new designations for buttons and axes. Vibration performance on HID standard devices and command processing in remote access applications have also been improved.
At the same time, the Nintendo Switch Pro controller was already supported by Steam, so this is not about introducing compatibility from scratch.
The update also speeds up connections via Steam Remote Play, fixes input transmission for the Steam Controller, and resolves a Linux client crash after the device wakes from sleep mode. Valve has not yet announced when the changes will appear in the stable version of Steam.