Facing the same problem. Two different websites. Without any code change, all Gemini answers became JSON instead of natural text some time yesterday evening, already leading to support requests from users. This makes Gemini completely unusable and we had to change to a competitor for the time being. Using Vercel AI SDK 5 and Vercel aI SDK 6 with standard Google provider on the different projects, which, again, worked flawlessly until yesterday evening when something changed on Google’s side.