OpenAI announced on August 6 that GPT-5.6 Luna is becoming the default model for ChatGPT's Free and Go tiers, replacing GPT-5.5 Instant, and that those users will get unlimited text chats with no rate limits — a first for the free tier. The rollout is staged: Luna became the default that week, with unlimited text chats and a new Think button following the week of August 10.

What free users get

Once fully rolled out, Free and Go users can chat with GPT-5.6 Luna without hitting the message caps that previously throttled heavy use of the free tier. The unlimited allowance covers text chats specifically; limits still apply to file uploads, image generation, and other ChatGPT tools, and OpenAI says the offering remains subject to its standard abuse guardrails. Free users also gain access to a Think button, which lets Luna spend more time reasoning through a harder question on a per-message basis rather than always answering at standard speed.

OpenAI cited an internal accuracy improvement behind the swap: responses containing at least one factual error were 62% less common with Luna than with the outgoing GPT-5.5 Instant default, the company said.

Paid tiers get a retuned Sol

The same announcement updated GPT-5.6 Sol for Plus and Pro subscribers, retuning it for everyday conversational use. Those users get a new effort slider in ChatGPT across web, mobile, and desktop that lets them dial reasoning depth from quick everyday replies up to extended effort for planning, research, writing, coding, and decision-heavy tasks.

Why it matters

ChatGPT is a service OpenAI says roughly 1 billion people use weekly, so a change to the free tier's default model and its rate limits reaches far more people than any single paid-tier feature launch. Putting a current-generation model behind an unlimited allowance for free users — rather than routing them to a cut-down legacy model, as ChatGPT has historically done — raises the baseline experience competitors like Google's Gemini and Anthropic's Claude are compared against, and signals OpenAI is willing to absorb more inference cost on its free tier to defend ChatGPT's consumer lead as rivals close the capability gap.