Solar Mini 4

Solar Mini 4 is a compact language model from Upstage, aimed at agentic applications where response speed and cost matter. Upstage's model documentation lists the snapshot solar-mini4-260922 (alias solar-mini4) as released on 22 September 2026, with a training-data cut-off of February 2026. The Korean publication AI Times reported on 14 September that Upstage's chief executive had announced a free preview on 13 September, with the paid API opening on the 22nd.

The model has 35 billion parameters in total, of which about 3 billion are active for each token. Upstage gives a 512K-token context window and up to 128K output tokens, and lists chat, a reasoning mode, structured outputs and tool calling. Input and output are supported in Korean, English and Japanese. It is available on the Upstage Console and Playground, and Upstage also offers it for on-premises deployment; no downloadable weights have been published.

Upstage's pricing page lists $0.10 per million input tokens, $0.01 per million cached input tokens and $0.40 per million output tokens, excluding 10% VAT. A 50% discount runs from 22 September to 22 October 2026 (UTC). The documentation states that API input data is not used for model training and is not stored unless required for service delivery.

AI Times reported on 18 September that a Sogang University mathematics team, evaluating the model on Korean university-entrance (CSAT) mathematics questions, recorded a 93.5% pass@3 rate. Upstage positions Solar Mini 4 as a smaller, cheaper counterpart to Solar Pro 4 for high-volume work. Buyers should test it on their own tasks, particularly in languages other than the three it supports.