Solar Pro 4

The flagship of South Korean lab Upstage's in-house Solar family, surfaced on developer platforms around Aug 10 2026 and formally unveiled Aug 14 2026. An agent-first reasoning model pitched as a reliable workhorse — 'save frontier models for frontier problems' — with strong office-productivity, document-intensive, and coding performance rather than raw frontier scores. Carries a 524K-token context and up to 131K output tokens. Upstage reports large gains over Solar Pro 3: ~71 on the AA-LCR long-document benchmark (about 2.3x its predecessor) and 23 on Tau3-Banking tool-use (a 2.6x jump); Artificial Analysis scores it 42 on its Intelligence Index. API pricing is $0.30 / $1.20 per 1M input/output tokens, with a launch promo cutting that 90% to $0.03 / $0.12. Upstage is the first Korean company registered as an official model provider alongside OpenAI, Anthropic, Google, and NVIDIA. Served via Upstage's API and OpenRouter; weights were not published at launch, so treated as proprietary.