How fast will GPT-OSS 20B feel on the MacBook M3 Max 48GB?

GPT-OSS 20B on the MacBook M3 Max 48GB

GPT-OSS 20B is a 20.91B-parameter mixture-of-experts model (3.6B active per token). At MXFP4 it needs about 12.9 GB of memory. The MacBook M3 Max 48GB has 36 GB usable, so it fits entirely in memory. Expect about 81 tokens/sec (64–98), with the first token after 0.3 s for a short prompt. This estimate is based on community benchmarks of this exact setup.

Speed by quantization

QuantizationFile sizeMemoryGenerationFirst tokenSource
MXFP412.1 GBFits81 tok/s0.3 sMeasured

GPT-OSS 20B on other hardware

Other models on the MacBook M3 Max 48GB

All models on the MacBook M3 Max 48GB · GPT-OSS 20B on all hardware

Estimates for a short prompt on a single device. Measured numbers come from community benchmarks (r/LocalLLaMA, localscore.ai and more); others are derived from similar setups or projected from specs. Open source on GitHub.