GPT-5.5 Instant Is Now the ChatGPT Default + `chat-latest` API Alias
TL;DR
GPT-5.5 Instant replaces GPT-5.3 Instant as ChatGPT's default model;
chat-latest now points to it โ 52.5% fewer hallucinated claims on high-stakes prompts, AIME 2025: 81.2 vs 65.4, MMMU-Pro: 76 vs 69.2 (vs GPT-5.3 Instant).Developer signal
Any code calling
chat-latest silently upgraded today. Pin gpt-5.3-instant if stability matters. Extended prompt caching behavior changed โ in-memory caching no longer supported. GPT-5.3 Instant remains accessible to paid users for 3 months.OpenAI | Date: 2026-05-05 | Link: https://openai.com/index/introducing-gpt-5-5/https://openai.com/index/gpt-5-5-system-card/ | https://developers.openai.com/api/docs/models/gpt-5.5