OpenAI Improves GPT-5.6 Sol in ChatGPT and Brings Luna to Free Users

OpenAI announced on August 6 a new round of improvements to GPT-5.6 Sol inside ChatGPT, while expanding access to GPT-5.6 Luna — its fastest and most affordable model — to free users. The update marks the latest step in the company's push to broaden distribution of the GPT-5.6 family it began publicly releasing last month.

Sol Gets Stronger in ChatGPT

In a product post published August 6, OpenAI said the flagship Sol model has been improved within ChatGPT, with the changes rolling out gradually to the global user base. Sol is the top tier of the GPT-5.6 family, launched for general availability on July 9 after a limited preview that had been coordinated with the U.S. government. The Verge reported at launch that Sol is priced at $5 per million input tokens and $30 per million output tokens — nearly half the cost of Anthropic's Claude Fable 5 — with Terra priced at half of Sol and Luna at less than half of Terra.

Luna Comes to Free Users

The August 6 post also confirmed that GPT-5.6 Luna, the family's most cost-efficient tier, is now available to free users of ChatGPT. The move follows a July 30 price adjustment in which OpenAI cut the price of Luna by 80% and Terra by 20%, according to the company's model page. OpenAI also said the GPT-5.6 series is available across ChatGPT, Codex, and the OpenAI API.

Speed and Safety

At the June preview, OpenAI said GPT-5.6 Sol would run on Cerebras hardware at up to 750 tokens per second, and that the company had dedicated roughly 700,000 A100e GPU hours to automated red-teaming ahead of release. The models are trained to refuse prohibited cyber assistance, including attempts to disguise intent or jailbreak the system, the company said. With Luna now in free users' hands, OpenAI is betting that its cheapest tier, not its flagship, is what finally brings frontier-grade AI to the mass market.