OpenAI ships GPT-5.5 — and makes the low-hallucination Instant variant ChatGPT's new default

GPT-5.5 positioned as more agentic; 5.5 Instant became the default ChatGPT model with reduced hallucination in law/medicine/finance; 5.5-Codex is the agentic-coding variant.

What it means GPT-5.5 Instant becoming ChatGPT's default with lower hallucination in law, medicine, and finance raises the reliability bar for the highest-stakes consumer use cases, while 5.5-Codex signals a dedicated agentic-coding line, not just a general-purpose model.