---
license: apache-2.0
tags:
- oscar
- int2
- kv-cache
- quantization
- rotation
- sglang
---

<p align="center">
  <img src="https://huggingface.co/Zhongzhu/OSCAR-RotationZoo/resolve/main/oscar_logo_kv_transparent.png" alt="OSCAR INT2 KV-Cache" width="180"/>
</p>

# OSCAR RotationZoo

Precomputed K/V rotation matrices for **OSCAR INT2 KV-cache quantization**.

- 📄 **Paper** — [*OSCAR: Offline Spectral Covariance-Aware Rotation for 2-bit KV Cache Quantization*](https://arxiv.org/pdf/2605.17757)
- 🌐 **Website** — https://oscar-quantize.github.io/
- 💻 **Code** — https://github.com/FutureMLS-Lab/OSCAR

OSCAR captures Q/K/V activations on a small calibration set, estimates
attention-aware K/V covariance offline, and derives per-layer orthogonal
rotations that align INT2 quantization with the directions attention actually
consumes. The result is ~7× compression of the KV-cache memory footprint with
single-digit pp accuracy drop on GPQA for dense reasoning models.

This repo packages the rotations as drop-in `.pt` files so you don't need to
re-run the Q/K/V dump and eigendecomposition yourself.

## Available rotations

| Model | Calibration | GPQA (BF16) | GPQA (OSCAR INT2) |
|---|---|---:|---:|
| `Qwen/Qwen3-4B-Thinking-2507` | `seq20000_prompt83_group128` | 67.27 | 67.17 |
| `Qwen/Qwen3-4B-Thinking-2507` | `seq20000_prompt85_group128` (fresh re-dump) | 67.27 | — |
| `Qwen/Qwen3-8B`               | `seq20000_prompt83_group128` | 56.67 | 55.56 |
| `Qwen/Qwen3-32B`              | `seq16000_prompt69_group128` | 58.49 | 60.40 |
| `zai-org/GLM-4.7-FP8`         | `seq10000_prompt43_group128` | 73.23 | 73.57 |

`seq<T>_prompt<N>_group<G>` notation: `T` = total calibration tokens,
`N` = calibration prompt count, `G` = INT2 quant group size along head_dim.

## File format

Each rotation directory contains:

- `k_rotation_qqt_r_h_pbr.pt` — K-side rotation `R_K = R · H · P_br` where
  `R = eigvec(Σ_Q)` is fit on Q's attention-aware covariance, `H` is a
  head-dim Hadamard, and `P_br` is the eigenvalue-sorted bit-reversal
  permutation
- `v_rotation_sst_r_h_pbr.pt` — V-side rotation built on the score-weighted
  V covariance `Σ_V = V^T diag(K^T (Q^T Q) K) V`

File layout (PyTorch state-dict):
```python
{
  "format_version": 1,
  "objective":      "qqt_r_h_pbr"      # or "sst_r_h_pbr" for V
  "source_grouping": "layer",
  "layers": {
    0:  {"layer_id": 0,  "rotation": tensor(head_dim, head_dim)},
    1:  {"layer_id": 1,  "rotation": tensor(head_dim, head_dim)},
    ...
  }
}
```

## How to use

### 1. Download the rotation for your model

```bash
pip install huggingface_hub
```

```python
from huggingface_hub import snapshot_download
snapshot_download(
    repo_id="Zhongzhu/OSCAR-RotationZoo",
    allow_patterns="Qwen3-8B/**",
    local_dir="./oscar_rotations",
)
# rotations now at ./oscar_rotations/Qwen3-8B/seq20000_prompt83_group128/
```

### 2. Serve with sglang-research using the rotation

Clone https://github.com/FutureMLS-Lab/OSCAR and set up the single `oscar`
conda env, then point the eval driver at your downloaded rotation:

```bash
ROT_DIR=./oscar_rotations/Qwen3-8B/seq20000_prompt83_group128 \
  bash rotation/qwen3-8B/eval_gpqa.sh
```

The driver internally launches sglang with these flags:

```bash
SGLANG_ENABLE_MIXED_KV_WINDOWS=1 \
SGLANG_OSCAR_ROTATION_MODE=oscar \
SGLANG_OSCAR_K_ROTATION_PATH=$ROT_DIR/k_rotation_qqt_r_h_pbr.pt \
SGLANG_OSCAR_V_ROTATION_PATH=$ROT_DIR/v_rotation_sst_r_h_pbr.pt \
SGLANG_OSCAR_K_CLIP_RATIO=0.96 \
SGLANG_OSCAR_V_CLIP_RATIO=0.92 \
SGLANG_OSCAR_ABSORB_V_ROTATION=1 \
SGLANG_MIXED_KV_PREFIX_TOKENS=64 \
SGLANG_MIXED_KV_RECENT_TOKENS=256 \
HADAMARD_ORDER=128 \
python -m sglang.launch_server \
  --model-path Qwen/Qwen3-8B \
  --tensor-parallel-size 1 \
  --kv-cache-dtype int2 \
  --kv-cache-quant-group-size 128 \
  --prefill-attention-backend fa3 \
  --decode-attention-backend triton \
  --disable-radix-cache \
  --disable-custom-all-reduce \
  --trust-remote-code
```

Sink (`PREFIX_TOKENS=64`) and recent window (`RECENT_TOKENS=256`) tokens stay
in BF16; the bulk of the KV cache is INT2-quantized into 128-element groups
along head_dim using these rotations.

## Reproducing from scratch

If you want to fit your own rotation on a different calibration set, the
OSCAR pipeline is end-to-end reproducible:

```bash
git clone https://github.com/FutureMLS-Lab/OSCAR.git
cd OSCAR
bash rotation/qwen3-8B/save_qkv_8b.sh        # phase 1 — dump Q/K/V
bash rotation/qwen3-8B/compute_rotation.sh   # phase 2 — fit R = eigvec(Σ_Q)
```

## Citation

```bibtex
@article{zhou2026oscar,
  title  = {OSCAR: Offline Spectral Covariance-Aware Rotation for 2-bit KV Cache Quantization},
  author = {Zhou, Zhongzhu and Zhuang, Donglin and Li, Jisen and Chen, Ziyan and Song, Shuaiwen Leon and Athiwaratkun, Ben and Wu, Xiaoxia},
  year   = {2026},
  note   = {Together AI; University of Sydney; UIUC},
}
```