I’m trying to play MWlll cross gen addition and every time it ask my to buy game pass to play

Is this even when i bought the game because I bought MWlll.

Yes. With the exception of "free to play" games all other games require having a gamepass core subscription in order to play online.

All.current consoles require a subscription with the exception of PC based consoles like steam deck or ROG which uses Windows

Hi, Afa! Thank you for your reply.

Yes, I'm afraid this applies to purchased games as well.

For your reference, this is mentioned on the listing for Call of Duty MW3:
https://www.xbox.com/games/store/call-of-duty-modern-warfare-iii---lote-multigeneracin/9NB54XTF084M

If you look at the game's age rating and warning, on the right side there you should see two labels:

"+Offers in-app purchases."

"Online multiplayer on console requires Xbox Game Pass Ultimate or Xbox Game Pass Core (sold separately)."

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Please let me know if you have any further questions, I'd be happy to help.
Best regards.

Is this even when i bought the game because I bought MWlll.

Hi, Afa! Thank you for reaching out.
I'm AJ, an Independent Advisor for the Xbox Community.
I'm sorry to hear you are experiencing issues playing MW3

With the exemption of Free-to-Play games like Fortnite, Apex Legends, Warzone, etc, console games require an active subscription to Game Pass Ultimate or Game Pass Core to access online features and play on the Xbox Network.

To clarify, this only applies to online game modes. You can still access your purchased games' Offline / Story modes without an active subscription to either of these services.

For your reference, Game Pass Core is what Xbox Live Gold used to be, it's just that it was renamed and restructured to offer additional services on top of online gaming and features.

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If you are trying to play a game online, I'm afraid this is the reason why you are being prompted to choose a subscription plan. As a fellow gamer, I understand this is probably not the answer you were hoping for. I'm sorry, Afa.

Please let me know if you have any further questions, I'd be happy to help.
Best regards.