gguf-quantization

Turns a downloaded AI model into a single self-contained file, shrunk by as much or as little as you choose, that ordinary desktop apps can open and run on your own machine.

WHEN TO USE

SCOPE

USE FOR

Convert a HuggingFace model to GGUF, then quantize it to a size that fits your hardware.
Run local inference on a laptop or an Apple Silicon Mac with no GPU required.
Feed in sample text first so quality holds up when the model is squeezed hardest.
Serve a GGUF model behind an OpenAI-compatible local API for existing client code.
Load a quantized GGUF model into Ollama, LM Studio, or text-generation-webui.

NOT FOR

For maximum accuracy with calibration on NVIDIA GPUs, use AWQ or GPTQ instead.
For fast, calibration-free quantization for HuggingFace, use HQQ instead.
For simple integration with the transformers library, use bitsandbytes instead.
For maximum-speed production NVIDIA deployment, use TensorRT-LLM instead.

This is a saved copy of the skill's SKILL.md instructions. It may differ from the upstream file or the version you install.

In this document (13)

GGUF - Quantization Format for llama.cpp

The GGUF (GPT-Generated Unified Format) is the standard file format for llama.cpp, enabling efficient inference on CPUs, Apple Silicon, and GPUs with flexible quantization options.

When to use GGUF

Use GGUF when:

Deploying on consumer hardware (laptops, desktops)
Running on Apple Silicon (M1/M2/M3) with Metal acceleration
Need CPU inference without GPU requirements
Want flexible quantization (Q2_K to Q8_0)
Using local AI tools (LM Studio, Ollama, text-generation-webui)

Key advantages:

Universal hardware: CPU, Apple Silicon, NVIDIA, AMD support
No Python runtime: Pure C/C++ inference
Flexible quantization: 2-8 bit with various methods (K-quants)
Ecosystem support: LM Studio, Ollama, koboldcpp, and more
imatrix: Importance matrix for better low-bit quality

Use alternatives instead:

AWQ/GPTQ: Maximum accuracy with calibration on NVIDIA GPUs
HQQ: Fast calibration-free quantization for HuggingFace
bitsandbytes: Simple integration with transformers library
TensorRT-LLM: Production NVIDIA deployment with maximum speed

Quick start

Installation

# Clone llama.cpp
git clone https://github.com/ggml-org/llama.cpp
cd llama.cpp

# Build (CPU)
make

# Build with CUDA (NVIDIA)
make GGML_CUDA=1

# Build with Metal (Apple Silicon)
make GGML_METAL=1

# Install Python bindings (optional)
pip install llama-cpp-python

Convert model to GGUF

# Install requirements
pip install -r requirements.txt

# Convert HuggingFace model to GGUF (FP16)
python convert_hf_to_gguf.py ./path/to/model --outfile model-f16.gguf

# Or specify output type
python convert_hf_to_gguf.py ./path/to/model \
    --outfile model-f16.gguf \
    --outtype f16

Quantize model

# Basic quantization to Q4_K_M
./llama-quantize model-f16.gguf model-q4_k_m.gguf Q4_K_M

# Quantize with importance matrix (better quality)
./llama-imatrix -m model-f16.gguf -f calibration.txt -o model.imatrix
./llama-quantize --imatrix model.imatrix model-f16.gguf model-q4_k_m.gguf Q4_K_M

Run inference

# CLI inference
./llama-cli -m model-q4_k_m.gguf -p "Hello, how are you?"

# Interactive mode
./llama-cli -m model-q4_k_m.gguf --interactive

# With GPU offload
./llama-cli -m model-q4_k_m.gguf -ngl 35 -p "Hello!"

Quantization types

K-quant methods (recommended)

Type	Bits	Size (7B)	Quality	Use Case
Q2_K	2.5	~2.8 GB	Low	Extreme compression
Q3_K_S	3.0	~3.0 GB	Low-Med	Memory constrained
Q3_K_M	3.3	~3.3 GB	Medium	Balance
Q4_K_S	4.0	~3.8 GB	Med-High	Good balance
Q4_K_M	4.5	~4.1 GB	High	Recommended default
Q5_K_S	5.0	~4.6 GB	High	Quality focused
Q5_K_M	5.5	~4.8 GB	Very High	High quality
Q6_K	6.0	~5.5 GB	Excellent	Near-original
Q8_0	8.0	~7.2 GB	Best	Maximum quality

Legacy methods

Type	Description
Q4_0	4-bit, basic
Q4_1	4-bit with delta
Q5_0	5-bit, basic
Q5_1	5-bit with delta

Recommendation: Use K-quant methods (Q4_K_M, Q5_K_M) for best quality/size ratio.

Conversion workflows

Workflow 1: HuggingFace to GGUF

# 1. Download model
huggingface-cli download meta-llama/Llama-3.1-8B --local-dir ./llama-3.1-8b

# 2. Convert to GGUF (FP16)
python convert_hf_to_gguf.py ./llama-3.1-8b \
    --outfile llama-3.1-8b-f16.gguf \
    --outtype f16

# 3. Quantize
./llama-quantize llama-3.1-8b-f16.gguf llama-3.1-8b-q4_k_m.gguf Q4_K_M

# 4. Test
./llama-cli -m llama-3.1-8b-q4_k_m.gguf -p "Hello!" -n 50

Workflow 2: With importance matrix (better quality)

# 1. Convert to GGUF
python convert_hf_to_gguf.py ./model --outfile model-f16.gguf

# 2. Create calibration text (diverse samples)
cat > calibration.txt << 'EOF'
The quick brown fox jumps over the lazy dog.
Machine learning is a subset of artificial intelligence.
Python is a popular programming language.
# Add more diverse text samples...
EOF

# 3. Generate importance matrix
./llama-imatrix -m model-f16.gguf \
    -f calibration.txt \
    --chunk 512 \
    -o model.imatrix \
    -ngl 35  # GPU layers if available

# 4. Quantize with imatrix
./llama-quantize --imatrix model.imatrix \
    model-f16.gguf \
    model-q4_k_m.gguf \
    Q4_K_M

Workflow 3: Multiple quantizations

#!/bin/bash
MODEL="llama-3.1-8b-f16.gguf"
IMATRIX="llama-3.1-8b.imatrix"

# Generate imatrix once
./llama-imatrix -m $MODEL -f wiki.txt -o $IMATRIX -ngl 35

# Create multiple quantizations
for QUANT in Q4_K_M Q5_K_M Q6_K Q8_0; do
    OUTPUT="llama-3.1-8b-${QUANT,,}.gguf"
    ./llama-quantize --imatrix $IMATRIX $MODEL $OUTPUT $QUANT
    echo "Created: $OUTPUT ($(du -h $OUTPUT | cut -f1))"
done

Python usage

llama-cpp-python

from llama_cpp import Llama

# Load model
llm = Llama(
    model_path="./model-q4_k_m.gguf",
    n_ctx=4096,          # Context window
    n_gpu_layers=35,     # GPU offload (0 for CPU only)
    n_threads=8          # CPU threads
)

# Generate
output = llm(
    "What is machine learning?",
    max_tokens=256,
    temperature=0.7,
    stop=["</s>", "\n\n"]
)
print(output["choices"][0]["text"])

Chat completion

from llama_cpp import Llama

llm = Llama(
    model_path="./model-q4_k_m.gguf",
    n_ctx=4096,
    n_gpu_layers=35,
    chat_format="llama-3"  # Or "chatml", "mistral", etc.
)

messages = [
    {"role": "system", "content": "You are a helpful assistant."},
    {"role": "user", "content": "What is Python?"}
]

response = llm.create_chat_completion(
    messages=messages,
    max_tokens=256,
    temperature=0.7
)
print(response["choices"][0]["message"]["content"])

Streaming

from llama_cpp import Llama

llm = Llama(model_path="./model-q4_k_m.gguf", n_gpu_layers=35)

# Stream tokens
for chunk in llm(
    "Explain quantum computing:",
    max_tokens=256,
    stream=True
):
    print(chunk["choices"][0]["text"], end="", flush=True)

Server mode

Start OpenAI-compatible server

# Start server
./llama-server -m model-q4_k_m.gguf \
    --host 0.0.0.0 \
    --port 8080 \
    -ngl 35 \
    -c 4096

# Or with Python bindings
python -m llama_cpp.server \
    --model model-q4_k_m.gguf \
    --n_gpu_layers 35 \
    --host 0.0.0.0 \
    --port 8080

Use with OpenAI client

from openai import OpenAI

client = OpenAI(
    base_url="http://localhost:8080/v1",
    api_key="not-needed"
)

response = client.chat.completions.create(
    model="local-model",
    messages=[{"role": "user", "content": "Hello!"}],
    max_tokens=256
)
print(response.choices[0].message.content)

Hardware optimization

Apple Silicon (Metal)

# Build with Metal
make clean && make GGML_METAL=1

# Run with Metal acceleration
./llama-cli -m model.gguf -ngl 99 -p "Hello"

# Python with Metal
llm = Llama(
    model_path="model.gguf",
    n_gpu_layers=99,     # Offload all layers
    n_threads=1          # Metal handles parallelism
)

NVIDIA CUDA

# Build with CUDA
make clean && make GGML_CUDA=1

# Run with CUDA
./llama-cli -m model.gguf -ngl 35 -p "Hello"

# Specify GPU
CUDA_VISIBLE_DEVICES=0 ./llama-cli -m model.gguf -ngl 35

CPU optimization

# Build with AVX2/AVX512
make clean && make

# Run with optimal threads
./llama-cli -m model.gguf -t 8 -p "Hello"

# Python CPU config
llm = Llama(
    model_path="model.gguf",
    n_gpu_layers=0,      # CPU only
    n_threads=8,         # Match physical cores
    n_batch=512          # Batch size for prompt processing
)

Integration with tools

Ollama

# Create Modelfile
cat > Modelfile << 'EOF'
FROM ./model-q4_k_m.gguf
TEMPLATE """{{ .System }}
{{ .Prompt }}"""
PARAMETER temperature 0.7
PARAMETER num_ctx 4096
EOF

# Create Ollama model
ollama create mymodel -f Modelfile

# Run
ollama run mymodel "Hello!"

LM Studio

Place GGUF file in ~/.cache/lm-studio/models/
Open LM Studio and select the model
Configure context length and GPU offload
Start inference

text-generation-webui

# Place in models folder
cp model-q4_k_m.gguf text-generation-webui/models/

# Start with llama.cpp loader
python server.py --model model-q4_k_m.gguf --loader llama.cpp --n-gpu-layers 35

Best practices

Use K-quants: Q4_K_M offers best quality/size balance
Use imatrix: Always use importance matrix for Q4 and below
GPU offload: Offload as many layers as VRAM allows
Context length: Start with 4096, increase if needed
Thread count: Match physical CPU cores, not logical
Batch size: Increase n_batch for faster prompt processing

Common issues

Model loads slowly:

# Use mmap for faster loading
./llama-cli -m model.gguf --mmap

Out of memory:

# Reduce GPU layers
./llama-cli -m model.gguf -ngl 20  # Reduce from 35

# Or use smaller quantization
./llama-quantize model-f16.gguf model-q3_k_m.gguf Q3_K_M

Poor quality at low bits:

# Always use imatrix for Q4 and below
./llama-imatrix -m model-f16.gguf -f calibration.txt -o model.imatrix
./llama-quantize --imatrix model.imatrix model-f16.gguf model-q4_k_m.gguf Q4_K_M

References

Advanced Usage - Batching, speculative decoding, custom builds
Troubleshooting - Common issues, debugging, benchmarks

Resources

Repository: https://github.com/ggml-org/llama.cpp
Python Bindings: https://github.com/abetlen/llama-cpp-python
Pre-quantized Models: https://huggingface.co/TheBloke
GGUF Converter: https://huggingface.co/spaces/ggml-org/gguf-my-repo
License: MIT

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