Apple won't take the risk of being blamed for AI answers being incorrect. They will attribute Google/Gemini so users know how to be mad at if it doesn't work as expected.

This is a double-edged sword. Apple would love any failure to be blamed on Google, but not the branding to go with it.

Apple's brand is so dominant that even if they say Siri is "powered by Google", most users will still perceive it as an Apple service. The only way that changes is if Apple consistently and prominently surfaces the Google name on Siri — which seems unlikely (but who knows when the stakes are so high).

Apple is already taking the risk of being blamed for their own AI right now, though (an AI that is much more prone to incredibly dumb errors than Gemini), so I don't find it that obvious that they wouldn't just continue taking the blame for Siri as they already do, except with an actually smarter Siri.