# GPT-OSS (20B)

> OpenAI's smaller open-weight MoE model favors width and alternating local/global attention.

| Property | Value |
| --- | --- |
| Lab | OpenAI (United States) |
| Released | 2025-08-04 |
| Decoder type | Sparse MoE |
| Family | Sparse MoE |
| Scale | 21B total, 3.6B active (17.1% active) |
| Context window | 128,000 tokens |
| Attention | GQA with alternating sliding-window and global layers |
| Layer mix | 12 sliding-window + 12 global |
| KV cache / token (bf16) | 48 KiB (Low) |
| License | Apache License 2.0 |

**Key detail:** Wider and shallower than Qwen3, with attention bias and sink mechanisms.

## 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.
- [Sliding Window Attention (SWA)](https://llm-atlas-7or.pages.dev/concepts/swa.md): Some layers only attend to a local window of recent tokens instead of the whole context.
- [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 9 (General 12.8, Scientific 6.2, Coding 19.4, Agents 0)

## Links

- Architecture diagram: https://sebastianraschka.com/llm-architecture-gallery/images/architectures/gpt-oss-20b.webp
- View in article: https://magazine.sebastianraschka.com/p/the-big-llm-architecture-comparison#%C2%A79-gpt-oss
- config.json: https://huggingface.co/openai/gpt-oss-20b/blob/main/config.json
- License: https://huggingface.co/openai/gpt-oss-20b/blob/main/LICENSE
- Tech report: https://cdn.openai.com/pdf/419b6906-9da6-406c-a19d-1bb078ac7637/oai_gpt-oss_model_card.pdf
- Source card (source of truth): https://sebastianraschka.com/llm-architecture-gallery/#card-gpt-oss-20b
- Web page: https://llm-atlas-7or.pages.dev/models/gpt-oss-20b/
- JSON: https://llm-atlas-7or.pages.dev/api/models/gpt-oss-20b.json

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