OpenAI GPT-5.5 Instant (May 2026): new ChatGPT default model + API `chat-latest`

OpenAI says GPT‑5.5 Instant is rolling out as ChatGPT’s new default model (replacing GPT‑5.3 Instant) and is also available in the API as chat-latest. (https://openai.com/index/gpt-5-5-instant/)

What OpenAI says shipped

According to OpenAI’s release post, the GPT‑5.5 Instant update focuses on:

• Smarter, more accurate answers with clearer, more concise responses. (gpt-5-5-instant/">https://openai.com/index/gpt-5-5-instant/)
• Improved factuality — OpenAI reports internal evals showing 52.5% fewer hallucinated claims vs GPT‑5.3 Instant on “high-stakes prompts” (medicine, law, finance), and 37.3% fewer inaccurate claims on conversations users flagged for factual errors. (gpt-5-5-instant/">https://openai.com/index/gpt-5-5-instant/)
• Less verbosity / overformatting and fewer unnecessary follow-up questions. (https://openai.com/index/gpt-5-5-instant/)
• Better handling of image/photo uploads, STEM questions, and deciding when to use web search. (https://openai.com/index/gpt-5-5-instant/)

New transparency controls: “memory sources”

OpenAI also says it’s introducing memory sources across ChatGPT models, which show what context was used when a response is personalized (for example, saved memories or past chats) and let you delete or correct that context. (https://openai.com/index/gpt-5-5-instant/)

Availability / rollout

OpenAI’s post includes these rollout notes:

• ChatGPT: GPT‑5.5 Instant is rolling out “starting today” to all ChatGPT users as the default model. (https://openai.com/index/gpt-5-5-instant/)
• API: OpenAI says GPT‑5.5 Instant is available in the API as chat-latest. (https://openai.com/index/gpt-5-5-instant/)
• Paid users: GPT‑5.3 Instant remains available for three months via model configuration settings before being retired. (https://openai.com/index/gpt-5-5-instant/)

Sources

• OpenAI: GPT‑5.5 Instant (May 2026): https://openai.com/index/gpt-5-5-instant/