# Reflection Beam (501B)

> Text-only MoE decoder with three dense FFN layers followed by 49 expert layers. Each MoE layer activates 8 of 256 experts without a shared expert.

| Property | Value |
| --- | --- |
| Lab | Reflection (United States) |
| Released | 2026-10-16 |
| Decoder type | Sparse MoE |
| Family | Sparse MoE |
| Scale | 501.3B total, 23.4B active (4.7% active) |
| Context window | 1,048,576 tokens |
| Attention | Gated GQA with QK-Norm and sliding-window/global attention |
| Layer mix | 43 sliding-window + 9 global GQA |
| KV cache / token (bf16) | 208 KiB (High) |
| License | Apache License 2.0 |

**Key detail:** Combines 512-token local RoPE attention with global NoPE and query scaling. Uses sandwich RMSNorm, depth-scaled residuals, and a final logit softcap of 30.

## 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.
- [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.
- [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.
- [QK-Norm (QK-Norm)](https://llm-atlas-7or.pages.dev/concepts/qk-norm.md): RMSNorm applied to queries and keys before attention to keep logits well-behaved.
- [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.

## Benchmark (Artificial Analysis Intelligence Index)

- AA Intelligence Index v5.0: total 17.7 (Knowledge Work 26.3, Coding 4.5, Science 10.9, General 29.2)

## Links

- Architecture diagram: https://sebastianraschka.com/llm-architecture-gallery/images/architectures/reflection-beam.webp
- config.json: https://huggingface.co/reflection/Beam-1.0-501B-A23B/blob/main/config.json
- License: https://huggingface.co/reflection/Beam-1.0-501B-A23B/blob/main/LICENSE
- Source card (source of truth): https://sebastianraschka.com/llm-architecture-gallery/#card-reflection-beam-501b
- Web page: https://llm-atlas-7or.pages.dev/models/reflection-beam-501b/
- JSON: https://llm-atlas-7or.pages.dev/api/models/reflection-beam-501b.json

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