ChatGPT Free Tier Goes Unlimited — and Defaults to Luna

OpenAI is taking the message counter off ChatGPT's free tier. In an update announced on August 6, the company said free users will get unlimited text-based chats, and that GPT-5.6 Luna will replace GPT-5.5 Instant as the default model on both the Free and Go plans.

The rollout is staged rather than instant. The refreshed GPT-5.6 Sol for Plus and Pro subscribers shipped immediately. The model swap for Free and Go users lands this week. Unlimited text chat itself arrives the week of August 10. The headline is also narrower than it sounds: only text is being uncapped. Separate limits stay in place for file uploads, image analysis, voice and image generation, so the free tier remains metered everywhere the compute is expensive.

A Think button on every tier

Alongside the cap change, both free and paid users get a Think button that forces higher-effort reasoning on a single message rather than for a whole conversation. Plus and Pro subscribers get a finer-grained version of the same control — a thinking slider that dials reasoning depth up or down per query. OpenAI describes the updated Sol as aimed at quick work: questions, web research, advice, planning, writing and decisions.

The company also put numbers on the accuracy gain. In internal testing on financial, medical and legal prompts that demand factual precision, responses containing at least one factual error were 62% less common with GPT-5.6 Luna and 68% less common with GPT-5.6 Sol, both measured against GPT-5.5 Instant. Those are vendor-reported figures from an internal evaluation, not an independent benchmark, and OpenAI has not published the prompt set.

Why the free tier could absorb this now

Uncapping the largest free chatbot audience in the world is a serving-cost decision before it is a product decision, and the cost side moved first. In late July OpenAI cut Luna's price by 80%, leaving Sol untouched and stretching the GPT-5.6 range to roughly 25x from cheapest to dearest tier. Luna is the cheap end of the family OpenAI shipped in June as Sol, Terra and Luna — which is precisely why it, and not Sol, is the model being handed to a billion-plus weekly users with no ceiling.

There is a competitive read too. ChatGPT recently passed one billion weekly users, but it slipped below 50% assistant market share earlier this summer as Gemini and Claude closed the gap. Removing the most visible friction point in the free product — the moment a conversation stops and asks you to upgrade or wait — is a retention move aimed squarely at that trend. Whether it holds depends on something OpenAI has not disclosed: what happens to per-user inference cost when the users who were previously rate-limited stop being rate-limited.