They are giving pointers to how to run it now using for example https://recipes.vllm.ai/Qwen/Qwen3.8-Flash-Next (and an especially provided vllm release).

Relevant PR: https://github.com/ggml-org/llama.cpp/pull/27742

This branch works now: https://github.com/unslothai/llama.cpp/tree/qwen4exp/qwen3.8...

  cmake -B build -DGGML_CUDA=ON

or

  cmake -B build -DGGML_METAL=ON

then

  cmake --build build --config Release -j --target llama-server llama-cli

Probably going to take a 1-3 days for support to land in llama.cpp and vllm.