GPT-5.5 Instant becomes ChatGPT's default, cutting hallucinations 52.5% on high-risk topics

OpenAI replaced ChatGPT's default model with GPT-5.5 Instant, which it says produces 52.5% fewer hallucinated claims on sensitive topics like law, medicine, and finance based on internal evals. A new 'memory sources' feature shows users which stored context shaped a response. The model maintains low latency and is rolling out to all users immediately.