OpenAI Switches GPT-5.5 Instant as Default Model, Hallucination Rate Drops 52.5%

On May 5, OpenAI replaced ChatGPT's default model with GPT-5.5 Instant. The company reports a 52.5% reduction in hallucination claims on high-risk prompts in healthcare, legal, and financial domains compared to GPT-5.3 Instant. Concurrently, OpenAI unveiled three new voice APIs—GPT-Realtime-2 (with 15 percentage-point audio benchmark improvement), Realtime-Translate (expanding from 70 to 13 languages), and Realtime-Whisper for live transcription—accelerating the practical AI cycle.