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Fine-grained FP8

docs/source/en/quantization/finegrained_fp8.md

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Fine-grained FP8

Fine-grained FP8 quantization quantizes the weights and activations to fp8.

  • The weights are quantized to 8-bits for each 2D block (weight_block_size=(128, 128)).
  • The activations are quantized to 8-bits for each group per token. The group value matches the weights in the input channel (128 by default).

FP8 quantization enables support for DeepSeek-V3 and DeepSeek-R1.

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[!TIP] You need a GPU with Compute Capability>=9 (H100), and install a PyTorch version compatible with the CUDA version of your GPU.

Install Accelerate and upgrade to the latest version of PyTorch.

bash
pip install --upgrade accelerate torch

Create a [FineGrainedFP8Config] class and pass it to [~PreTrainedModel.from_pretrained] to quantize it. The weights are loaded in full precision (torch.float32) by default regardless of the actual data type the weights are stored in. Set dtype="auto" to load the weights in the data type defined in a models config.json file to automatically load the most memory-optimal data type.

py
from transformers import FineGrainedFP8Config, AutoModelForCausalLM, AutoTokenizer

model_name = "meta-llama/Meta-Llama-3-8B"
quantization_config = FineGrainedFP8Config()
quantized_model = AutoModelForCausalLM.from_pretrained(model_name, dtype="auto", device_map="auto", quantization_config=quantization_config)

tokenizer = AutoTokenizer.from_pretrained(model_name)
input_text = "What are we having for dinner?"
input_ids = tokenizer(input_text, return_tensors="pt").to(quantized_model.device.type)

output = quantized_model.generate(**input_ids, max_new_tokens=10)
print(tokenizer.decode(output[0], skip_special_tokens=True))

Use [~PreTrainedModel.save_pretrained] to save the quantized model and reload it with [~PreTrainedModel.from_pretrained].

py
quant_path = "/path/to/save/quantized/model"
model.save_pretrained(quant_path)
model = AutoModelForCausalLM.from_pretrained(quant_path, device_map="auto")

DeepGEMM fast path

On Hopper (SM90+) and Blackwell (SM100+) GPUs, every FP8 linear automatically dispatches to the DeepGEMM kernels from kernels-community/deep-gemm when weight_block_size=(128, 128) and activation_scheme="dynamic". DeepGEMM is 3-6x faster than the Triton fallback. Install or upgrade the kernels package to enable it.

bash
pip install -U kernels

DeepGEMM JIT-compiles its kernels, so the CUDA toolchain (nvcc/nvrtc) must be available. The required CUDA runtime depends on the hardware, 12.3+ on Hopper and 12.9+ on Blackwell.

If the kernel cannot load (missing kernels, unsupported GPU, missing CUDA toolchain, or older CUDA), Transformers logs a warning once and falls back to the Triton finegrained-fp8 kernel. Static activation quantization always stays on the Triton path.

To force the Triton fallback even when DeepGEMM is available, set TRANSFORMERS_DISABLE_DEEPGEMM_LINEAR=1. This only affects the FP8 linear dispatch and leaves the "deepgemm" experts backend untouched, which you switch with [~PreTrainedModel.set_experts_implementation].

For MoE experts, the DeepGEMM path is opt-in. Pass experts_implementation="deepgemm" (or "deepgemm_megamoe" on Blackwell) at load time to route the expert matmuls through DeepGEMM. See the Experts backends guide for the full set of options.

UE8M0 scale format

DeepSeek V4-style checkpoints store FP8 weight scales in the packed float8_e8m0fnu format instead of float32. These checkpoints are pre-quantized and set scale_fmt="ue8m0" in their quantization config. Both the DeepGEMM and Triton kernels read UE8M0 scales, so these checkpoints run on either path.