What is Solar Open 2?
Solar Open 2 is Upstage's open-weight flagship, released on 22 July 2026. It is a mixture-of-experts model with 250 billion parameters, 15 billion active per token, and a 1M-token context. Three of every four layers use linear attention, which keeps a fixed-size memory instead of a growing cache, so only 12 of its 48 layers store a KV cache. Upstage built it for agent work in office productivity, documents and coding, and it officially supports English, Korean and Japanese. Reasoning is either off or on, capped at 131,072 tokens.
The weights are under the Upstage Solar License: Apache 2.0 plus a rule that any derivative model you distribute must carry the Solar name and show "Built with Solar". Commercial use, fine-tuning and distillation are allowed. Upstage lists four H200 GPUs as the minimum and eight as recommended, and Nota AI publishes official INT4 and NVFP4 builds. On Hugging Face it has 760 likes and 8,027 downloads in the last 30 days.
There is no shared per-token API. Upstage's free Playground trial ended on 31 July, and FlexAI rents it only as a dedicated 16-H100 endpoint at $3.50 per GPU-hour. Upstage's paid API sells Solar Pro 4, a separate closed model.
How much does Solar Open 2 cost?
| Plan | Price | What you get |
|---|---|---|
| Weights | Free | Upstage Solar License |
| FlexAI dedicated endpoint | $56.00/hour | 16 H100 GPUs at $3.50/GPU-hour, billed per minute |
Free weights under the Upstage Solar License (Apache 2.0 plus Solar branding for derivatives). No per-token API; FlexAI dedicated endpoint $3.50/GPU-hour on 16 H100s ($56.00/hour).
Is Solar Open 2 worth it?
On Upstage's numbers Solar Open 2 is among the best open models for Korean office work, and close to DeepSeek-V4-Flash in English. Upstage reports 86.2 on MMLU-Pro and 92.4 on LiveCodeBench, the top scores in its comparison, and 70.4 on SWE-Bench Verified against 73.8 for DeepSeek-V4-Flash. On Ko-GDPval, Upstage's test of 170 Korean work scenarios, it scores 86.8, a fraction behind DeepSeek-V4-Pro's 86.9 with a third of its active parameters.
It is weaker on terminal work. Upstage's own table gives it 28.3 on Terminal Bench Hard against 41.7 for MiMo-V2.5 and 34.1 for DeepSeek-V4-Flash, and its GDPval-AA rating of 1128 is below DeepSeek-V4-Flash's 1187.
The catch: there is nowhere to try it cheaply. The free Playground trial closed on 31 July, no shared API serves it, and FlexAI's dedicated endpoint costs $56.00 an hour, about $40,880 for a month of uptime. Serving needs Upstage's fork of vLLM until mainline support lands. Derivatives you publish must carry the Solar name.
Our take: Solar Open 2 is a sensible base for a Korean company that already owns a GPU node and wants an open model that writes good Korean without a Chinese-lab licence. Teams without hardware will find DeepSeek-V4-Flash, at $0.15 and $0.29 per million tokens on OrcaRouter, far easier.
Where it earns its place
A Korean enterprise IT team with an eight-GPU H200 server
Run an in-house assistant for Korean reports, spreadsheets and email
Serve the BF16 weights with Upstage's vLLM fork on the H200 node. Upstage says its tokenizer needs 50 to 80% as many tokens as global models for Korean text, which stretches the 1M-token context further.
A developer who wants Claude Code on a local model
Run Claude Code or Hermes Agent against a self-hosted open model
One vLLM server exposes both an Anthropic-compatible /v1/messages endpoint and an OpenAI-compatible /v1 endpoint, so Claude Code and Hermes Agent connect with a few environment variables.
Before you commit
- Setup
- Download from Hugging Face and serve with Upstage's vLLM v0.22.0 fork, by Docker image or from source; Transformers needs Upstage's branch and fla-core for fast kernels.
- Integrations
- OpenAI-compatible and Anthropic-compatible endpoints from vLLM; OpenAI-style tool calling with the solar_open2 parser; MCP tools through Claude Code or Hermes Agent.
- Data and privacy
- Self-hosted only, so prompts stay on your hardware; Upstage's API no longer serves it. Derivatives you distribute must use the Solar name and show Built with Solar.
- Cost at scale
- FlexAI's dedicated 16-H100 endpoint costs $56.00 an hour, billed per minute. Owning four to eight H200 GPUs, or two H100s with Nota AI's INT4 build, is the cheaper route for steady traffic.
- Limits
- 1M-token context; reasoning capped at 131,072 tokens, and max_tokens counts reasoning, so short limits return empty answers.
What’s good
- Only 15B active parameters and a KV cache on a quarter of its layers
- 1M-token context
- Ko-GDPval 86.8, level with DeepSeek-V4-Pro, per Upstage
- Apache 2.0 terms apart from Solar branding on derivatives
What’s not
- No shared per-token API anywhere
- Weaker on terminal-based agent tasks than MiMo-V2.5 and DeepSeek-V4-Flash
- Needs Upstage's vLLM fork
- Only three officially supported languages
Best for
Korean companies with their own GPUs that want an open model for Korean and English documents and agent work.
Solar Open 2 alternatives
Solar Open 2: common questions
- Is Solar Open 2 worth it?
- A capable and efficient Korean-English open model that you will have to host yourself, because nobody sells it by the token. We rate it 3.7 out of 5.
- How much does Solar Open 2 cost?
- Free weights under the Upstage Solar License (Apache 2.0 plus Solar branding for derivatives). No per-token API; FlexAI dedicated endpoint $3.50/GPU-hour on 16 H100s ($56.00/hour).
- What are the downsides of Solar Open 2?
- No shared per-token API anywhere; weaker on terminal-based agent tasks than MiMo-V2.5 and DeepSeek-V4-Flash; needs Upstage's vLLM fork; only three officially supported languages.
- Who is Solar Open 2 best for?
- Korean companies with their own GPUs that want an open model for Korean and English documents and agent work.
- How much does Solar Open 2 cost for a team or in production?
- FlexAI's dedicated 16-H100 endpoint costs $56.00 an hour, billed per minute. Owning four to eight H200 GPUs, or two H100s with Nota AI's INT4 build, is the cheaper route for steady traffic.
- Is Solar Open 2 safe for company data?
- Self-hosted only, so prompts stay on your hardware; Upstage's API no longer serves it. Derivatives you distribute must use the Solar name and show Built with Solar.
- What are the best Solar Open 2 alternatives?
- The closest alternatives we have reviewed are DeepSeek-V4.1-Flash, K-EXAONE 2.0, MiMo-V2.6-Pro and Command A+.
Answers checked Nov 7, 2026.