RuntimeError
llamacpp.RuntimeError: Metal GPU acceleration initialization failed on macOS
Stack trace
Traceback (most recent call last):
File "app.py", line 42, in <module>
model = Llama(model_path="./model.bin", use_metal=True)
File "llamacpp/__init__.py", line 88, in __init__
self._init_metal()
File "llamacpp/__init__.py", line 120, in _init_metal
raise RuntimeError("Metal GPU acceleration initialization failed on macOS")
RuntimeError: Metal GPU acceleration initialization failed on macOS Why it happens
llama.cpp attempts to use Apple's Metal API for GPU acceleration on macOS, but this requires compatible hardware, up-to-date drivers, and proper environment variables. If the GPU is unsupported, drivers are outdated, or environment variables are missing, initialization fails with this error.
Detection
Check for RuntimeError exceptions during model initialization with use_metal=True and verify system GPU compatibility and driver versions before running.
Causes & fixes
macOS device GPU does not support Metal or is too old
Run on a Mac with a Metal-compatible GPU (generally Macs from 2012 or later) or disable Metal acceleration by setting use_metal=False.
Missing or outdated macOS GPU drivers or system updates
Update macOS to the latest version to ensure Metal drivers are current and compatible with llama.cpp.
Environment variable LLAMACPP_USE_METAL is not set or incorrectly set
Set environment variable LLAMACPP_USE_METAL=1 before running your Python script to enable Metal acceleration properly.
llama.cpp library version lacks proper Metal support or has a bug
Upgrade to the latest llama.cpp version that includes stable Metal GPU acceleration support on macOS.
Code: broken vs fixed
from llamacpp import Llama
model = Llama(model_path="./model.bin", use_metal=True) # Raises RuntimeError on unsupported Mac
print("Model loaded")import os
from llamacpp import Llama
os.environ["LLAMACPP_USE_METAL"] = "1" # Ensure Metal acceleration env var is set
model = Llama(model_path="./model.bin", use_metal=True) # Fixed: Metal init succeeds on supported Mac
print("Model loaded with Metal GPU acceleration")Workaround
If Metal GPU acceleration fails, catch the RuntimeError and fallback to CPU by initializing Llama with use_metal=False to continue running without GPU acceleration.
Prevention
Verify macOS hardware supports Metal and keep the system updated; explicitly set LLAMACPP_USE_METAL=1 in your environment and test GPU initialization during deployment.