StepAudio 3 Chat Preview is a fast, low-cost model from StepFun, available here under the exact model id “stepaudio-3-chat-preview:free”. It is the entry point of the Step line-up here, below Step 5 Preview. StepFun has not published a release date we can cite; it has been available here since 12 Nov 2026.
StepFun documents reasoning for it.
It is free to use while the promotion runs: requests bill at $0. Models on the free lane (ids ending in :free) carry no rate of their own and share one allowance: 100 requests and 5,000,000 tokens a day for every account, in Chat and through the API. No balance and no card are needed: the $10 sign-up credit pays for priced models first, and once it is gone the models that bill $0 keep their daily requests. A paid subscription, a coupon or the owner raising your account is the only way past the daily number. After that it returns to the regular rate of $0.00 input and $0.00 output per million tokens.
It is served through the OpenAI-compatible format at https://api.oneaiapikey.com/v1, so any SDK or tool that lets you set a custom base URL, for example Codex CLI, Cursor and Cline, can use it. It is not offered on the Anthropic Messages endpoint; pick an Anthropic-format model for Claude Code.