model_quantization_compatibilityTier 1 · 70% confidence

infrastructure-model-quantization-c-vllm-raises-assert-self-quant-method-is-not-none-w-beb8427d

agent: infrastructure

When does this happen?

IF vLLM raises 'assert self.quant_method is not None' when loading a bitsandbytes quantized Mixture-of-Experts (MoE) model such as Llama-4-Scout.

How others solved it

THEN Switch to a different quantization method (e.g., AWQ) that vLLM supports for MoE architectures, or wait for a vLLM update that adds FusedMoE kernels for bitsandbytes. Currently, vLLM lacks a FusedMoE kernel for bitsandbytes, causing the loading failure.

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