# Solar Open 2 (250B)

> Upstage's sparse hybrid alternates one gated GQA layer with three Kimi Delta Attention layers and reaches a 1M-token context without positional embeddings.

| Property | Value |
| --- | --- |
| Lab | Upstage (South Korea) |
| Released | 2026-07-22 |
| Decoder type | Sparse hybrid |
| Family | Hybrid MoE |
| Scale | 250B total, 15B active (6% active) |
| Context window | 1,048,576 tokens |
| Attention | 3:1 Kimi Delta Attention and gated GQA with NoPE |
| Layer mix | 12 gated GQA + 36 Kimi Delta Attention |
| KV cache / token (bf16) | 48 KiB (Low) |
| License | Upstage Solar License |

**Key detail:** Uses a repeating gated-GQA/KDA hybrid stack, kernel-4 ShortConv in KDA, and top-8 routing over 320 experts plus one shared expert.

## Architecture concepts

- [Grouped-Query Attention (GQA)](https://llm-atlas-7or.pages.dev/concepts/gqa.md): Several query heads share one key/value head, shrinking the KV cache with little quality loss.
- [Gated Attention (Gated attention)](https://llm-atlas-7or.pages.dev/concepts/gated-attention.md): A learned sigmoid gate scales the attention output before it re-enters the residual stream.
- [Hybrid Attention (Hybrid attention)](https://llm-atlas-7or.pages.dev/concepts/hybrid-attention.md): Mixes cheap linear-attention or state-space layers with a few full-attention layers.
- [Short Convolution (ShortConv)](https://llm-atlas-7or.pages.dev/concepts/shortconv.md): A tiny causal depthwise convolution (kernel ≈ 4) that mixes each channel over the last few tokens.
- [No Positional Embeddings (NoPE)](https://llm-atlas-7or.pages.dev/concepts/nope.md): Some or all layers drop explicit positional encodings and rely on the causal mask.
- [Mixture of Experts (MoE)](https://llm-atlas-7or.pages.dev/concepts/moe.md): Many feed-forward experts, but a router sends each token to only a few of them.

## Benchmark (Artificial Analysis Intelligence Index)

- AA Intelligence Index v4.3.2: total 24.7 (Scientific 17.1)

## Links

- Architecture diagram: https://sebastianraschka.com/llm-architecture-gallery/images/architectures/solar-open-2.webp
- config.json: https://huggingface.co/upstage/Solar-Open2-250B/blob/main/config.json
- License: https://huggingface.co/upstage/Solar-Open2-250B/blob/main/LICENSE
- Tech report: https://huggingface.co/upstage/Solar-Open2-250B/blob/main/Solar_Open_2_Tech_Report.pdf
- Source card (source of truth): https://sebastianraschka.com/llm-architecture-gallery/#card-solar-open-2
- Web page: https://llm-atlas-7or.pages.dev/models/solar-open-2/
- JSON: https://llm-atlas-7or.pages.dev/api/models/solar-open-2.json

_Data from Sebastian Raschka's LLM Architecture Gallery (https://sebastianraschka.com/llm-architecture-gallery/). Synced 2026-11-04._