Upstage releases Solar Pro 4, tripling its Artificial Analysis Intelligence Index score

South Korean AI lab Upstage released Solar Pro 4 on August 11, 2026, a proprietary flagship reasoning model that independent tracker Artificial Analysis scored 42 on its Intelligence Index, triple the 14 its predecessor earned.

The jump vaults a Korean lab into the frontier conversation. Upstage says Solar Pro 4 is the first Korean model to appear on the Arena leaderboards for Agent Arena, Code Arena: WebDev and Text Arena, community rankings for AI systems.

Upstage introduced the model with a 512,000-token context window, up to 128,000 output tokens and an adjustable ‘reasoning-effort dial’ that trades speed for depth. It replaces Solar Pro 3, which shipped in April 2026.

On the company’s own numbers, Solar Pro 4 lifts its Terminal-Bench v2.1 score to 57% from 12% and its AA-LCR long-context score to 71% from 31%. Those agentic and long-context gains are Upstage’s figures; the Intelligence Index score comes from Artificial Analysis, which tests models independently.

Pricing runs $0.30 per million input tokens and $1.20 per million output tokens at standard rates, discounted 90% through September 10, 2026. The model is available via Upstage’s API, OpenRouter, SolarChat and Nous Research’s Hermes Agent platform.

A single independent score does not make a frontier model, and the discount will end. But Solar Pro 4 gives Upstage its strongest claim yet to sit alongside the US and Chinese labs that dominate the leaderboards.