Can I Run GPT-OSS 120B on Apple M5 Max?
Written by Jakub Rusinowski · Last updated September 29, 2026
Yes. GPT-OSS 120B needs 71.9 GB at 8K context (70.5 GB weights + 1.4 GB KV cache/overhead) at Q4_K_M and the Apple M5 Max has 96 GB usable, leaving about 24.1 GB of headroom, at roughly 77 tok/s (estimated) with room for up to 128K of context.
See what else this hardware can run →
The numbers
| Model | GPT-OSS 120B |
| Parameters | 120B |
| Quantization | Q4_K_M |
| VRAM needed (8K context) | 71.9 GB |
| Apple M5 Max usable memory | 96 GB |
| Verdict | Runs |
| Max context | 128K |
| Estimated speed | ~77 tok/s |
GPT-OSS 120B on the Apple M5 Max: VRAM by quantization
| Quant | VRAM needed | Fits 128 GB? | Max context | Whole PC |
|---|---|---|---|---|
| F16 | 235 GB | ✗ No | — | — |
| Q8_0 | 125.5 GB | ✗ No | — | — |
| Q6_K | 97.2 GB | ✗ No | — | — |
| Q5_K_M | 84.2 GB | ✓ Yes | 128K | — |
| Q4_K_M | 71.9 GB | ✓ Yes | 128K | — |
| Q3_K_M | 51.2 GB | ✓ Yes | 128K | — |
| Q2_K | 39.8 GB | ✓ Yes | 128K | — |
Assumes an 8K-token context with an f16 KV cache. A longer window needs more; a quantized KV cache needs less. “Max context” is the largest window that still fits in 128 GB of unified memory. Figures are estimates from parameter count, quantization and memory bandwidth — the analyzer lets you tune KV-cache quant and context.
Context costs VRAM too. At Q4_K_M on the Apple M5 Max: 8K 71.9 GB · 32K 73.7 GB · 128K 81 GB. Every window this model publishes still fits 128 GB.
What to do next
Nothing to change — run it at Q4_K_M. If you want more capability, check whether the next size up also fits.
No compatible GPU? GPT-OSS 120B on 96 GB of system RAM, CPU only: runs, but it is tight.
Running GPT-OSS 120B on this card:
GPT-OSS 120B needs ~72 GB but this GPU has 128 GB. Rent a A100 (80 GB)-class GPU by the hour instead of buying one:
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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 M5 Max
- GPT-OSS 20B — runs (12.3 GB)
GPT-OSS 120B on nearby hardware
- NVIDIA RTX PRO 6000 Blackwell (96 GB) — runs
All GPT-OSS sizes on the Apple M5 Max | GPT-OSS 120B model page | Apple M5 Max GPU page | VRAM calculator | Check your hardware