Upstage said on Wednesday it has unveiled 'Solar Open 2', an open-weight large language model (LLM) optimised for agent task execution. It released the model weights on the open-source platform Hugging Face.

Solar Open 2 was developed in-house by Upstage through a government sovereign AI foundation model project. Based on its previous 'Solar Open', it is tailored for agent use that completes tasks through repeated reasoning and tool calls.

Solar Open 2 has 250 billion parameters. It applies a mixture-of-experts (MoE) structure that activates only 15 billion parameters in actual work. It can process up to 1 million tokens. With model compression through quantisation, it can be deployed on in-house infrastructure using two Nvidia H200 chips.

Upstage said Solar Open 2 surpassed DeepSeek's 'V4 Flash', Mistral's 'Medium 3.5' and Cohere's 'Command A+' across overall knowledge (MMLU-Pro), coding (LiveCodeBench), instruction following (IFBench), tool calling (MCP-Atlas) and agent overall evaluation (APEX-Agents). It added that key benchmark scores, including knowledge and science reasoning (GPQA-Diamond), maths (HMMT) and coding, rose by more than 20 points from the previous version.

Upstage said it also scored higher than OpenAI's 'GPT-5.4 Mini' and Anthropic's 'Claude Haiku 4.5' in the overall average of Korean-language benchmarks. In a domestic real-world work evaluation (Ko-GDPval), it scored 86.75 points. That is similar to DeepSeek's 'V4 Pro', which has a parameter scale more than six times larger.

Solar Open 2 allows commercial use and development of derivative models under the 'Upstage Solar Licence (based on Apache 2.0)'. Upstage also released a technical report containing the architecture, training methodology and evaluation conditions.

Upstage will expand conversational agent services by applying Solar Open 2 to the portal 'Daum'. Through its AI agent platform 'Timely', it will also support the adoption of agents by local governments and public and educational institutions.

Upstage plans to expand Solar Open 2-based AX services across all industries with a consortium, including finance, legal, medical, public, defence, manufacturing, consumer goods, robotics and education. It aims to build 'full-stack sovereign AI' that connects infrastructure, models and services by combining a homegrown neural processing unit (NPU). It also plans to list Solar Open 2 on the global platforms OpenRouter and Hermes Agent.

Upstage CEO Sung Hoon Kim (김성훈) said, "Solar Open 2 is a model built with an emphasis on agent usability that completes work on its own in real workplaces, beyond simple benchmark scores." He said, "By releasing it as open-weight, we will advance the AI research ecosystem and, based on that, expand industry AX to secure Korea's leadership in sovereign AI."