The Surface Pro 3 and Surface Pro 2 tablets are getting some update love today through Windows Update, so expect the latest drivers to show up for manual download from the Surface software, firmware, and drivers page soon.
The primary reason for the firmware update is a new graphics driver to hopefully continue fixing Miracast issues. But, due to compatibility issues, both UEFI and the audio driver needed their own updates, too.
Per the update history page:
Surface Pro 3 UEFI update (v3.11.850.0 for SP3, v184.108.40.206 for SP2) includes changes needed for compatibility with the updated graphics driver.
HD Graphics Family driver update (v10.18.14.4170) improves graphics performance and includes better Miracast (wireless display) support.
Display Audio driver update (v6.16.00.3172) improves audio experience and supports compatibility with the updated graphics driver.
After the firmware update is installed, the update history will show: System Firmware Update – 5/19/2015