Can I run gpt-oss-20b on a Mac with 128 GB?

Yes

Its published weights (13.8 GB) fit in the 96.0 GB a Mac with 128 GB can use, with room for ≈ 128K tokens of context.

Full analysis of gpt-oss-20b Everything that runs on Mac with 128 GB Get the weights on Hugging Face

hf download openai/gpt-oss-20b

Files and context on Mac with 128 GB

Each file of gpt-oss-20b (and of GGUF versions the site has analyzed), and how much context fits next to it, with the context cache in 16-bit or 8-bit.

File	Size	On Mac with 128 GB	Context (16-bit)	Context (8-bit)
As published	13.8 GB	Fits	128K	128K
4-bit (estimate)	11.8 GB	Fits	128K	128K

gpt-oss-20b on other hardware

NVIDIA H100Yes
RTX 5090Yes
RTX 4090Yes
RTX 3090Yes
RTX 5060 Ti 16 GBYes, just
RTX 3060 12 GBNo
RTX 4060No
Mac with 32 GBYes
Mac with 64 GBYes
Mac with 128 GBYes

Popular models that run on Mac with 128 GB

Qwen3-0.6BQwen · 752M
Qwen3-VL-8B-InstructQwen · 8.77B
gpt2openai-community · 137M
tiny-Qwen2ForCausalLM-2.5trl-internal-testing · 2.44M
Qwen3-8BQwen · 8.19B
Qwen3-Coder-30B-A3B-Instruct-GGUFunsloth · 30.5B
gemma-4-26B-A4B-itgoogle · 25.8B
Qwen3.6-35B-A3B-FP8Qwen · 36.0B

Assumes 75% of the Mac's memory is usable (macOS's default limit for the GPU; it can be raised) and at least 4K tokens of context for one conversation, with the context cache in 16-bit unless noted. Fits leaves at least 20% of that memory for context; Tight leaves less.