---
base_model: mistralai/Mistral-Small-4-119B-2603
library_name: transformers
license: apache-2.0
tags:
  - rotorquant
  - kv-cache-quantization
  - mistral
  - moe
  - sparse-moe
  - multimodal
  - quantized
  - 256k-context
  - thinking
pipeline_tag: text-generation
---

# Mistral-Small-4-119B-RotorQuant

**KV cache quantization for Mistral Small 4 using RotorQuant** -- 5.3x faster prefill, 28% faster decode, with near-lossless quality (perplexity 6.91 vs 7.07 baseline).

This repository provides RotorQuant KV cache quantization support for [mistralai/Mistral-Small-4-119B-2603](https://huggingface.co/mistralai/Mistral-Small-4-119B-2603). Model weights are unchanged (FP16); only the KV cache is quantized during inference.

## Model Specs

| Property | Value |
|---|---|
| Base Model | Mistral Small 4 (March 2026) |
| Total Parameters | 119B |
| Active Parameters | 6.5B per token (Sparse MoE) |
| Architecture | Sparse MoE -- 128 experts, 4 active per token |
| Context Length | 256K tokens |
| Modality | Text + Images (multimodal) |
| Capabilities | Thinking / reasoning, tool use, multilingual |
| License | Apache 2.0 |
| Quantization | KV cache only (RotorQuant) |

## What is RotorQuant?

[RotorQuant](https://github.com/scrya-com/rotorquant) is a rotation-based KV cache quantization method that applies learned rotations before quantizing the key-value cache. Key results:

- **5.3x faster prefill** compared to unquantized baseline
- **28% faster decode** throughput
- **Perplexity: 6.91** vs 7.07 for unquantized (lower is better -- RotorQuant actually improves quality due to outlier suppression)
- Default 3-bit quantization with minimal quality loss

## Memory Estimates

| Component | FP16 Baseline | RotorQuant 3-bit |
|---|---|---|
| Model Weights | ~238 GB | ~238 GB |
| KV Cache (256K ctx) | ~32 GB | ~6.5 GB |
| **Total** | **~270 GB** | **~244.5 GB** |

> **Note:** This is a Sparse MoE model -- only 6.5B parameters are active per token, so inference is fast despite the 119B total parameter count.

## Quickstart

```python
from transformers import AutoModelForCausalLM, AutoTokenizer
from turboquant import IsoQuantCache

model_id = "majentik/Mistral-Small-4-119B-RotorQuant"

tokenizer = AutoTokenizer.from_pretrained(model_id)
model = AutoModelForCausalLM.from_pretrained(
    model_id,
    torch_dtype="auto",
    device_map="auto",
)

# Enable RotorQuant KV cache
cache = IsoQuantCache(model)

messages = [
    {"role": "user", "content": "Explain sparse mixture-of-experts architectures."}
]

inputs = tokenizer.apply_chat_template(messages, return_tensors="pt").to(model.device)
outputs = model.generate(
    inputs,
    max_new_tokens=512,
    past_key_values=cache,
)
print(tokenizer.decode(outputs[0], skip_special_tokens=True))
```

## See Also

- [mistralai/Mistral-Small-4-119B-2603](https://huggingface.co/mistralai/Mistral-Small-4-119B-2603) -- Base model
- [majentik/Mistral-Small-4-119B-TurboQuant](https://huggingface.co/majentik/Mistral-Small-4-119B-TurboQuant) -- TurboQuant KV cache variant
- [majentik/Mistral-Small-4-119B-RotorQuant-MLX-4bit](https://huggingface.co/majentik/Mistral-Small-4-119B-RotorQuant-MLX-4bit) -- MLX 4-bit weight-quantized + RotorQuant
- [RotorQuant GitHub](https://github.com/scrya-com/rotorquant)