I don't think they have much to do with stripe. I'm guessing they want to round out their business more and include payments for AI since OpenRouter is basically just an AI traffic router that takes your money and provides it to the APIs you use.

I wrote a substantial comment about this a few days ago: https://news.ycombinator.com/item?id=49324405

My guess: your LLM agent makes buying decisions for you. Providers of agents can integrate witg stripe. Those using openrouter click a button for micropayment support.