Leanstral-RotorQuant

RotorQuant KV cache compression for mistralai/Leanstral-2603.

This is a documentation repository that explains how to combine Leanstral's weights with RotorQuant inference-time KV cache compression. No weights are stored here — use the base model directly and apply RotorQuant via the Python package or llama.cpp fork.

Hardware compatibility

Device	VRAM / RAM	Recommendation
Any host that runs the base model	baseline + runtime savings	RotorQuant/TurboQuant is a KV-cache runtime modifier; pair with any weight variant

What is this?

KV cache compression reduces the memory used by the attention cache during inference. Unlike weight quantization (which is baked into the GGUF/MLX file), KV cache compression is applied at runtime — so the same base weights can be used with or without compression.

Technique	Where it's applied	Savings
Weight quantization (GGUF/MLX/AWQ)	Baked into model file	Reduces disk + weight memory
RotorQuant KV cache	At inference time	Reduces attention memory (critical for long context)

Both can be combined for maximum efficiency.

Quickstart

Option A — Python / transformers

Install the rotorquant package:

pip install rotorquant

Then use it with the base model:

import torch
from transformers import AutoModelForCausalLM, AutoTokenizer
from rotorquant import IsoQuantCache

tokenizer = AutoTokenizer.from_pretrained("mistralai/Leanstral-2603", trust_remote_code=True)
model = AutoModelForCausalLM.from_pretrained(
    "mistralai/Leanstral-2603",
    torch_dtype=torch.bfloat16,
    device_map="auto",
    trust_remote_code=True,
)

# Apply RotorQuant to the KV cache
cache = IsoQuantCache(bits=4)  # or bits=2 for more aggressive compression

inputs = tokenizer("Hello, how are you?", return_tensors="pt").to(model.device)
outputs = model.generate(
    **inputs,
    max_new_tokens=128,
    past_key_values=cache,
    use_cache=True,
)
print(tokenizer.decode(outputs[0][inputs["input_ids"].shape[-1]:], skip_special_tokens=True))

Option B — llama.cpp / LM Studio / Ollama (with fork)

RotorQuant KV cache types (iso3) are not in upstream llama.cpp. They require:

• llama-cpp-turboquant fork

Once built:

llama-cli -m Leanstral.gguf \
  --cache-type-k iso3 --cache-type-v iso3 \
  -ngl 99 -fa \
  -p "Hello"

For standard runtimes (LM Studio, Ollama, upstream llama.cpp), use conventional KV cache types (q8_0, q4_0). You lose the RotorQuant-specific benefits but keep GGUF weight quantization.

Model Specifications

Property	Value
Base Model	mistralai/Leanstral-2603
Architecture	Sparse MoE (128 experts, 4 active)
Parameters	119B total (MoE)
Context Length	256K
BF16 Size	~238 GB
Modalities	Text
License	apache-2.0

What is RotorQuant?

RotorQuant is a KV cache compression method based on Clifford algebra (Cl(3,0)) rotors — a faster, more parameter-efficient alternative to Google's TurboQuant. Uses lightweight block-diagonal rotations (independent 2D/4D rotations per pair/quartet) achieving O(d) complexity instead of O(d log d), fully parallelisable with no inter-element dependencies.

Benchmarks (from the RotorQuant repository, Llama 3.1 8B on RTX 5090 — results vary by model and hardware):

• Prefill: 3,822 tok/s (vs TurboQuant 722 tok/s)
• Decode: 119 tok/s (vs TurboQuant 93 tok/s)
• Perplexity: 6.91 (vs TurboQuant 7.07)
• Parameters: 4 per rotor (vs TurboQuant 16,384)

Benchmarks are from the RotorQuant repository using Llama 3.1 8B. Performance on Leanstral will differ. Please open a discussion if you have independent results.

Current Ecosystem Support

Runtime	RotorQuant Support	Notes
Python transformers + rotorquant	✅ Full	Drop-in cache class
llama.cpp upstream	❌ Not merged	Use fork below
llama-cpp-turboquant fork	✅ planar3, iso3	GitHub
LM Studio	❌ Requested	Use q8_0 as alternative
Ollama	❌ Not supported	Use OLLAMA_KV_CACHE_TYPE=q8_0
vLLM	❌ Not supported	—
koboldcpp	❌ Not supported	—

Pre-quantized weight variants

If you want combined weight + KV cache compression, majentik hosts pre-quantized versions:

• MLX (Apple Silicon)
• GGUF (llama.cpp / Ollama / LM Studio)

See Also

• RotorQuant GitHub
• TurboQuant paper (arXiv 2504.19874)
• llama-cpp-turboquant fork
• Base model: mistralai/Leanstral-2603
• Leanstral announcement

Variants in this family

(Showing 8 sibling variants under majentik/leanstral-*. The current variant — RotorQuant — is bolded.)

Variant	Runtime	Approx size	Use case
RotorQuant	runtime modifier	n/a	KV-cache root (weight-agnostic)
RotorQuant-MLX-2bit	mlx-lm	card-only	Apple Silicon, smallest
RotorQuant-MLX-4bit	mlx-lm	card-only	Apple Silicon balanced
RotorQuant-MLX-8bit	mlx-lm	card-only	Apple Silicon reference
TurboQuant	runtime modifier	n/a	KV-cache root (weight-agnostic)
TurboQuant-MLX-2bit	mlx-lm	card-only	Apple Silicon, smallest
TurboQuant-MLX-4bit	mlx-lm	card-only	Apple Silicon balanced
TurboQuant-MLX-8bit	mlx-lm	card-only	Apple Silicon reference