NVFP4 quantization of swiss-ai/Apertus-8B-2509 — part of the Swiss AI Apertus model family. 8B dense transformer supporting 1,811 languages with 65K context.

W4A4 — both weights and activations in FP4. Maximum speed on Blackwell GPUs. See also Apertus-8B-2509-NVFP4A16 for the weight-only W4A16 variant.

Key Specs

	Original (BF16)	NVFP4 (this)
Size on disk	~16 GB	~5 GB
Compression	—	~3.0x
Parameters	8B	8B
Architecture	Dense transformer, xIELU activation	same
Context window	65,536 tokens	65,536 tokens
Languages	1,811	1,811

Serving with vLLM

bash

vllm serve bg-digitalservices/Apertus-8B-2509-NVFP4 \
  --quantization modelopt \
  --dtype auto \
  --kv-cache-dtype fp8 \
  --gpu-memory-utilization 0.85 \
  --max-model-len 65536 \
  --trust-remote-code

DGX Spark

bash

VLLM_NVFP4_GEMM_BACKEND=marlin vllm serve bg-digitalservices/Apertus-8B-2509-NVFP4 \
  --quantization modelopt \
  --dtype auto \
  --kv-cache-dtype fp8 \
  --max-model-len 65536 \
  --trust-remote-code

Testing

This is a base model.

Quantization Details

Method: NVIDIA Model Optimizer (modelopt) v0.43
Format: NVFP4 — E2M1 weights with per-group FP8 scales (group size 16)
Calibration: 4096 samples from CNN/DailyMail, batch size 32, seq_len 1024
Hardware: NVIDIA H200 GPU
Quantization script: included as quantize.py

About Apertus

Apertus is built by Swiss AI — a fully open, privacy-first model family trained on 4,096 GH200 GPUs. Key features:

1,811 native languages
Novel xIELU activation + AdEMAMix optimizer
EU AI Act compliant, respects opt-out consent
Full training transparency (weights, data, scripts all public)

License

Apache 2.0 — inherited from the base model.

Citation

If you use this model, please cite the original Apertus work:

bibtex

@misc{swisstransformer2025apertus,
  title   = {Apertus},
  author  = {Swiss Transformer},
  year    = {2025},
  url     = {https://huggingface.co/swiss-ai}
}

Credits

Quantized by Mario Iseli on an NVIDIA H200. Built and validated with AI-engineering assistance from Anthropic.

📬 mario@marioiseli.com ☕ Buy me a coffee if this makes your inference go brrrrrr! 🚀