Can I Run GPT-OSS 20B on Apple M1 Ultra?

Written by Jakub Rusinowski · Last updated August 15, 2026

Yes. GPT-OSS 20B needs 10.6 GB at MXFP4 and the Apple M1 Ultra has 128 GB, leaving about 117.4 GB of headroom, at roughly 36 tok/s (estimated) with room for up to 128K of context.

The numbers

ModelGPT-OSS 20B
Parameters20B
QuantizationMXFP4
VRAM needed10.6 GB
Apple M1 Ultra VRAM128 GB
VerdictRuns
Max context128K
Estimated speed~36 tok/s

What to do next

Nothing to change — run it at MXFP4. If you want more capability, check whether the next size up also fits.

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Running GPT-OSS 20B on this card:

Apple Mac Studio M1 Ultra
128 GB VRAM · 60 W board power
2026 prices are volatile — check the current listing.
Check price on Amazon

Buy vs. rent GPT-OSS 20B
Buy the GPU
~$3,999
Apple M1 Ultra · MSRP
Rent by the hour
from $0.34/hr
RTX 4090 (24 GB) class

At 2 hrs/day, buying (~$3,999) beats renting at $0.34/hr after about 16.3 years.

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RunPod $0.34/hr
Rent on RunPod →
Vast.ai $0.35/hr · typical low · varies
Rent on Vast.ai →

Cloud rates verified 2026-07 — estimates, and marketplace prices vary. Buying price is GPU MSRP only, not a full PC.

Other GPT-OSS sizes on the Apple M1 Ultra

GPT-OSS 20B on nearby hardware

All GPT-OSS sizes on the Apple M1 Ultra | VRAM calculator for GPT-OSS 20B | Apple M1 Ultra GPU page | Check your hardware