FPS Boost uses Direct3D tweaks to deliver up to 4x higher framerates for the Xbox Series S and Xbox Series X
When Microsoft announced that it would be bringing FPS Boost to the Xbox Series S and Series X, it did not explain how the technology works. Thankfully, Digital Foundry has done so, with Richard Leadbetter and John Linneman explaining that:
Microsoft's Xbox compatibility team is working its magic this time around to adjust frame-rate caps at the Direct3D level
Currently, Microsoft has enabled FPS Boost on Far Cry 4, New Super Lucky's Tale, Sniper Elite 4, UFC 4 and Watch Dogs 2. However, Microsoft's approach of making high-level adjustments means that it should require less effort to enable FPS Boost on more games. Accordingly, Microsoft states that it will 'announce and release more titles featuring FPS Boost soon'.
FPS Boost is more than just a gimmick, too. As Digital Foundry's video below shows, FPS Boost increases framerates fourfold in New Super Lucky's Tale, and two-fold in the other four launch games. Additionally, the Xbox Series X can utilise Xbox One X enhancements and FPS Boost simultaneously, which allows it to run New Super Lucky's Tale at 120 FPS and 4K.
Overall, FPS Boost seems like an excellent feature for backwards compatible games. While Digital Foundry suggests that FPS Boost is live now, Microsoft clarifies that new menu icons and system settings will arrive in a spring system update.