We did that on a game I worked on over ten years ago. It was a mobile game and we knew that it was very important to player retention (and interest in multiplayer) to have the first multiplayer interaction be "fun". So we would simulate the first person you played against as though they were another human. Based on play data of other humans. Because you only played them once you didn't think you were playing a bot.

Where we used AI (machine learning, not LLM) was in terms trying to figure out what kind of human you would want to play with. We also used machine learning to try figure out what cohort of players you were in so we could tweak engagement.

Where LLMs could really shine, in my opinion: Gamers love to play people, not AI (now). People are unpredictable, they communicate, they play well but in ways a human could (like they don't have superhuman reflexes or speed). You can play all kinds of games against AI (StarCraft, Civilization, training of all kinds of FPS) but it isn't fun for long because you see the robotic patterns. However, an LLM might be able to mix it up like humans, talk to you, and you could probably make it have imperfect reaction time, coordination, etc. That would really help a lot of games that have lulls in human player activity, or too much toxicity.

I would be shocked if some games aren't doing this now. It seems like it still be hard to make a bot seem human, and it probably only works if you sprinkle it in.

Humans prefer humans over bots in multiplayer. Even if you dumb down LLM-powered-bots, there's no sense of accomplishment on beating a bot that can be dialed up-or-down. And the social aspect... maybe some amount of gamers want to talk to bots instead of humans in a pvp match. Curious on the numbers there.

Could never prove it, but would bet money that Marvel Snap for example is doing it right now.

Edit : oh yeah. A quick google search proved it : https://marvelsnapzone.com/bots/