A UEFI and System Aggregator (SAM) firmware update that enhances system stability, reliability, reduces power consumption, and improves touch latency with the touchpad on the Surface Type Cover and Surface Touch Cover
By the way, Microsoft did release four updates for the Windows 8.1 preview as part of today's Patch Tuesday, as Pureinfotech.com notes. Even though the Softies didn't mention these in their update history pages for Surface RT and Pro, I see my Surface RT running the 8.1 preview now has five updates to install.
Just a reminder: With ARM-based Surface RTs, automatic updating is always on. With the Intel-based Pros, Windows turns on automatic update during setup unless users decide to turn it off. (If you do so, you won't be notified when firmware updates are available.) Even if automatic updating is turned on, users can opt to proactively grab the firmware updates before they receive notification of their availability using Windows Update on their devices via these steps.
Microsoft officials previously told me that users of non-Surface Windows RT devices also can and should get updates (firmware and otherwise). "OEMs can (and are) providing any needed firmware or driver updates using Windows Update. These updates are targeted to specific Windows RT models. Recommended OS updates are available to all Windows RT devices at the time they are published. End-user settings will determine whether they are installed automatically," a Microsoft spokesperson told me a while back.