GPT-5.5 Instant: The New ChatGPT Default Model Complete Guide 2026
GPT-5.5 Instant replaced GPT-5.3 Instant as the ChatGPT default model on May 5, 2026, with 52.5% fewer hallucinated claims in high-stakes domains, Gmail personalization, and a new Memory Sources transparency feature. Full breakdown of what changed, the API migration path, and when to pin to the old model. Continue reading the full article on WowHow → Originally published at https://wowhow.cloud/blogs/gpt-5-5-instant-chatgpt-default-model-hallucination-gmail-2026