[simonw]

I couldn't get the downloadable binary to work, or the binary I compiled myself:

  ./SwiftLM \
    --model mlx-community/Qwen3.5-122B-A10B-4bit \
    --stream-experts \
    --port 5413

Error:

  [SwiftLM] Loading model: mlx-community/Qwen3.5-122B-A10B-4bit
  [SwiftLM] Enabled Async SSD Streaming on directory: e9c67b08899964be5fdd069bb1b4bc8907fe68f5
  [SwiftLM]  Memory strategy: FULL GPU (69.6GB model, 133.4GB available)
  [SwiftLM] Download: [===================>] 100% ⠋ (66395.4 MB / 66395.4 MB) | Speed: 0.0 MB/s      
  MLX error: Failed to load the default metallib. library not found library not found library not found library not found  at /Users/runner/work/SwiftLM/SwiftLM/LocalPackages/mlx-swift/Source/Cmlx/mlx-c/mlx/c/stream.cpp:115

[simonw]

Claude Code helped me figure out this recipe (inspired by a similar workaround in the CI scripts):

  git clone --recursive https://github.com/SharpAI/SwiftLM.git
  cd SwiftLM

  swift build -c release

  # Trick to copy in that missing mlx.metallib file
  uv run --with mlx-metal python -c "
  import importlib.metadata, pathlib, shutil
  d = importlib.metadata.distribution('mlx-metal')
  metallib = pathlib.Path(d._path).parent / 'mlx/lib/mlx.metallib'
  shutil.copy(metallib, '.build/release/')
  print(f'Copied {metallib} -> .build/release/mlx.metallib')

  # Now start the server (downloads 69GB Qwen model)
  .build/release/SwiftLM \
    --model mlx-community/Qwen3.5-122B-A10B-4bit \
    --stream-experts \
    --port 5413

But the server crashed when I tried to run a prompt through it:

  freed pointer was not the last allocation

[aegis_camera]

the Python mlx-metal trick is actually what's crashing it. The mlx.metallib from pip is a different version of MLX than what your Swift binary was built against. It gets past the startup error but then corrupts the GPU memory allocator at inference time → freed pointer was not the last allocation.

Use the version-matched metallib that's already in the repo:

cp LocalPackages/mlx-swift/Source/Cmlx/mlx/mlx/backend/metal/kernels/default.metallib \ .build/release/ .build/release/SwiftLM \ --model mlx-community/Qwen3.5-122B-A10B-4bit \ --stream-experts \ --port 5413 This is the exact metallib that was compiled alongside the Swift code — no version mismatch. Future pre-built releases will bundle it automatically.

[aegis_camera]

git clone https://github.com/SharpAI/SwiftLM # no --recursive needed cd SwiftLM swift build -c release ### Please let me know if this fix the issue:

# Copy metallib next to the binary (one-time step) cp LocalPackages/mlx-swift/Source/Cmlx/mlx/mlx/backend/metal/kernels/default.metallib \ .build/release/