I hope that this is the mandate for everything they do.
Edit:
Optimized for Xbox Series X is the indicator for games that take advantage of the full power of Xbox Series X. Since Xbox Series X offers developers unparalleled power and speed, this empowers them to create the experiences they want and embrace a range of features and capabilities based on what is best for their individual titles... Games featuring the Optimized for Xbox Series X badge can showcase anything from virtually eliminating load times via the Xbox Velocity Architecture, heightened visuals, and hardware-accelerated DirectX raytracing powered by our custom, next-generation GPU, to steadier and often higher framerates up to 120 FPS... such as Halo Infinite... Games that have been Optimized for Xbox Series X use the power of the new console to deliver higher, steadier frame rates, with a performance target of 60 FPS at 4K resolution. Some games will even be able to support frame rates up to 120 FPS or variable refresh rates, allowing developers to offer players heightened realism and more precise controls for fast-paced action.
My inference from this is that Halo Infinite is going to have a mode, probably multiplayer, that runs at 120fps. Maybe at 1440p with a temporal solution to 4K. Until I see otherwise, I'm going into this thinking single player will be 60fps, possibly at 4K native. If it can't, I want to see the trade-off but I'm pretty confident we are going to see at least 60fps for Halo Infinite.