AMD recently held at event in Korea for its new R5 CPUs. During the presentation, the company showed a video that featured several PC games, and it was spotted in the video that there was artwork from Halo 3. This led to speculation that Halo 3 could be arriving for the PC, because after all why else would AMD show Halo 3 if there are no plans to bring it to the PC, right?
One could chalk it up to an accident in the sense that maybe someone used the wrong artwork, but according to DSO Gaming, there has been talk that there might be a Halo 3 Anniversary version of the game that could be revealed by Microsoft at E3 2017 in June, so perhaps the artwork could be hinting at that.
In any case take it with a grain of salt for now, but if you enjoyed Halo 3 and wouldn’t mind playing the game on your PC, then this could be worth looking forward to. However until it is official, maybe try not to get your hopes up.