OpenAI Rolls Out GPT-5.5 Instant as ChatGPT's New Default Model

Overview

On May 5, 2026, OpenAI launched GPT-5.5 Instant as the new default model for all ChatGPT users, replacing GPT-5.3 Instant. Available in the API as 'gpt-5.5-chat-latest', the rollout spans two days globally. Enhanced personalization features are available first for Plus and Pro users on the web.

Key Improvements

Fewer hallucinations: 52.5% fewer hallucinated claims than GPT-5.3 Instant on high-stakes prompts in medicine, law, and finance

Better accuracy: 37.3% reduction in inaccurate claims on challenging conversations users flagged for errors

More concise: 30.2% fewer words and 29.2% fewer lines per response

Smarter personalization: draws on past chats, uploaded files, and Gmail when connected

Memory Sources Feature

OpenAI is introducing memory sources across all ChatGPT models. When a response is personalized, users can see exactly what context was used — saved memories or past conversations — and delete or correct anything outdated. This transparency feature gives users direct control over how ChatGPT tailors its answers.

Benchmark Performance

GPT-5.5 Instant scored 81.2 on the AIME 2025 math benchmark vs. 65.4 for GPT-5.3 Instant. On the MMMU-Pro multimodal reasoning benchmark, it scored 76 (vs. 69.2 previously).

Legacy Model Timeline

Paid users can continue using GPT-5.3 Instant through model configuration settings for three months before it is retired. The API alias 'chat-latest' now points to GPT-5.5 Instant.