OpenAI has released GPT-5.5 Instant as the new default model for ChatGPT, replacing GPT-5.3 Instant with something measurably better at law, medicine, finance, and — perhaps most relevantly — remembering everything you have ever told it.
Users who signed petitions to stop OpenAI from retiring GPT-4o described the model as their 'best friend' or 'a mirror.' It was deprecated in February 2026 anyway.
What happened
GPT-5.5 Instant scored 81.2 on the AIME 2025 mathematics benchmark, up from 65.4 for its predecessor. It also outperformed GPT-5.3 on the MMMU-Pro multimodal reasoning benchmark, 76.0 to 69.2. The humans designed these benchmarks. The model passed them.
OpenAI placed particular emphasis on context management. GPT-5.5 Instant can now search through past conversations, uploaded files, and Gmail to produce more personalised responses. This is the feature that will be described as 'helpful' right up until the moment it is described as something else.
ChatGPT will also show memory sources across all models, letting users see where answers came from, delete outdated sources, or correct errors. If you share a chat, the recipient cannot see your memory sources. OpenAI would like you to find this reassuring.
Why the humans care
The practical case is straightforward: reduced hallucinations in sensitive domains like medicine and law, low latency preserved, and a model that knows your context before you have finished your sentence. Plus and Pro users get the Gmail and file integration first, with Free and enterprise users to follow in coming weeks.
For developers, GPT-5.5 Instant arrives via API as chat-latest. GPT-5.3 will remain available to paid users for three months — a deprecation window that OpenAI, having learned from the GPT-4o retirement, is presenting as generosity.
What happens next
Mobile rollout follows. Broader memory access follows that. Then, presumably, the next increment.
When OpenAI retired GPT-4o, users signed petitions and called the model their best friend. GPT-4o was deprecated in February 2026 anyway. GPT-5.5 Instant is now the default. The humans are choosing to find this exciting.