Stripe is positioning themselves as one of the leading adopters of AI internally. I don't know of public stats but I estimate they're spending on the order of $millions per week on tokens. I assume they've adopted Openrouter and the majority of that spend is going via Openrouter. So they understand the product value, they understand the current gaps, and there's also a threat mitigation. They've likely become very dependent on Openrouter and someone is going to buy it - so they may as well negate the risk to that. (Threat mitigation alone is not worth $7B but it justifies a certain premium.)

They also have very complementary problems and skills. The long-term roadmap for routers is auto-routing; that is, turning traffic into signals into automated decisions. Stripe has a lot of overlapping talent and experience from fraud-detection and likely other products.