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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 with improved factuality, tighter responses, and new memory-source transparency controls; it’s also available in the API as `chat-latest`.

By Authority AI Tools Editorial Team•2026-05-16•10 min read

Last reviewed: 2026-05-16

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Authority AI Tools Editorial Team

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The Authority AI Tools editorial team maintains this directory using vendor documentation, dated source checks, product changelogs, and clearly identified hands-on observations where available.

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/)

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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/

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