Base Model: chromadb/context-1 (fine-tuned from openai/gpt-oss-20b)
Architecture: 20B parameter Mixture of Experts (MoE) with 32 experts, 4 active per token
Format: MLX with MXFP4 quantization
Quantization: 4.504 bits per weight

Performance (Apple M1 Max, 64GB)

Metric	Value
Model Size	11 GB
Peak Memory	12 GB
Generation Speed	~69 tokens/sec
Prompt Processing	~70 tokens/sec
Latency	~14.5 ms/token

Usage

python

from mlx_lm import load, generate

model, tokenizer = load("foadmk/context-1-MLX-MXFP4")
response = generate(model, tokenizer, prompt="What is the capital of France?", max_tokens=100, verbose=True)

Conversion Notes

The chromadb/context-1 model uses a different weight format than the original openai/gpt-oss-20b, which required custom conversion logic:

Key Differences from Original Format

Dense BF16 tensors (not quantized blocks with _blocks suffix)
gate_up_proj shape: (experts, hidden, intermediate*2) with interleaved gate/up weights

Weight Transformations Applied

gate_up_proj (32, 2880, 5760):
- Transpose to (32, 5760, 2880)
- Interleaved split: [:, ::2, :] for gate, [:, 1::2, :] for up
- Result: gate_proj.weight and up_proj.weight each (32, 2880, 2880)
down_proj (32, 2880, 2880):
- Transpose to match MLX expected format
Bypass mlx_lm sanitize: Pre-naming weights with .weight suffix to skip incorrect splitting

Conversion Script

A conversion script is included in this repo: convert_context1_to_mlx.py

python convert_context1_to_mlx.py --output ./context1-mlx-mxfp4

Intended Use

This model is optimized for:

Context-aware retrieval and search tasks
Running locally on Apple Silicon Macs
Low-latency inference without GPU requirements

Limitations

Requires Apple Silicon Mac with MLX support
Best performance on M1 Pro/Max/Ultra or newer with 32GB+ RAM
Model outputs structured JSON-like responses (inherited from base model training)

Citation

If you use this model, please cite the original:

bibtex

@misc{chromadb-context-1,
  author = {Chroma},
  title = {Context-1: A Fine-tuned GPT-OSS Model for Retrieval},
  year = {2025},
  publisher = {HuggingFace},
  url = {https://huggingface.co/chromadb/context-1}
}

Acknowledgments

chromadb for the original context-1 model
OpenAI for the gpt-oss-20b base model
Apple MLX team for the MLX framework
mlx-community for MLX model conversion tools