Post-apocalyptic FPS S.T.A.L.K.E.R. 2 will only be exclusive to Xbox for about three months before it's able to move to other consoles. S.T.A.L.K.E.R. 2 was announced as an Xbox console exclusive last summer, allowing Microsoft to pad out its offerings by supporting an indie game with extreme potential. That said, a recent court filing suggests that it's only a timed exclusive for now.
Developer GSC Game World recently stated in an interview that there are no plans for S.T.A.L.K.E.R. 2 on other platforms "for now". The careful emphasis on "for now" definitely seems to suggest that the studio will want to bring the game to PlayStation 5 after the exclusivity window has lifted, but likely can't say anything due to contractual deals. Whether the studio will actually follow through remains to be seen.
A court filing for the ongoing Epic v Apple case (via Reddit user velspire) reveals Microsoft's various exclusivity deals for a handful of games and notes that S.T.A.L.K.E.R. 2 is slated for a Q4 2021 release and will be exclusive to Xbox and PC for 3 months. After that, it seems GSC Game World can do what it wants with the game, but Xbox will have an advantage no matter what since S.T.A.L.K.E.R. 2 is on Xbox Game Pass day one.
Of course, there could be room for Xbox and GSC Game World to possibly up the contract depending on a variety of factors. Xbox has been incredibly bullish about acquiring studios, so it's not out of the question to imagine the team getting purchased outright should it deliver a really remarkable title. The document also appears to be somewhat dated as there are games listed on its 2020 line-up like Call of Duty: Black Ops Cold War which are labeled as "unannounced" and games like Outriders have different release windows. It's possible that Xbox and GSC Game World have already made adjustments to the S.T.A.L.K.E.R. 2 deal.
Not much of S.T.A.L.K.E.R. 2 has been seen yet, but given the acclaimed nature of other games in the series, it's no surprise that Xbox fought hard to get exclusive access for a sliver of time. It's likely that the platform holder will try and hold details of its exclusivity close to the chest, so as to lure as many people into Xbox and Xbox Game Pass as possible. Regardless of when the exclusivity does end, it's not a guarantee that GSC Game World will even port it to PlayStation 5. That said, it would seem more likely than not that an indie developer would want to capitalize on as many consoles as possible.
Source: Microsoft court filing, velspire/Reddit