GPT‑5.6 Luna expands to free users as Sol receives a ChatGPT update

OpenAI is making GPT‑5.6 Luna the default model for Free and Go users during the week, with unlimited text and a Think button due the following week; tool access remains limited. Plus and Pro users receive an updated GPT‑5.6 Sol in ChatGPT and a reasoning-effort slider. OpenAI reports fewer factual-error responses than GPT‑5.5 Instant, but the figures—about 62% for Luna and 68% for Sol—are internal evaluations. The Work/Codex version of Sol is unchanged.

Impact: broader reasoning access may increase adoption and inference demand. Buyers should independently evaluate accuracy, latency, usage limits and task economics, and avoid carrying ChatGPT results over to Codex without testing.