Solar Pro 4

Solar Pro 4 is a flagship large language model developed by Upstage AI, designed for complex reasoning and high-reliability agentic workflows. Unveiled in August 2026, the model marks a transition in the Solar series toward "finishable work"—the ability to complete multi-step tasks such as document synthesis, data reconciliation, and sequential decision-making. It is recognized as a high-performing reasoning system, achieving an intelligence score of 42 on the Artificial Analysis Index, which positions it alongside other frontier-class models.

The model's architecture focuses on behavioral reliability, intended to minimize stalled steps and hallucinations in professional settings. In benchmark evaluations, Solar Pro 4 demonstrated significant improvements over its predecessors, scoring 57 on Terminal-Bench v2.1 for completing jobs in live shells and 71 on the AA-LCR benchmark for reasoning across long-document filings. It is specifically engineered to report when evidence is insufficient for a task rather than generating unverifiable outputs.

A central feature of Solar Pro 4 is its 524,288-token context window, which enables it to process large document sets, repositories, or data files in a single session. The model includes a "reasoning effort" setting that allow users to adjust the depth of analysis, facilitating a balance between high-intensity reasoning for complex problems and lower-latency responses for real-time interactions. It supports native multilingual processing for English, Korean, and Japanese.

Solar Pro 4 is primarily provided as a commercial API and is optimized for integration into enterprise document processing solutions and autonomous agent frameworks. Its performance metrics on multi-turn tool use and long-horizon planning tasks are designed to meet the requirements of financial and corporate sectors where ROI depends on the successful completion of automated end-to-end jobs.