Can I Run GPT-OSS on Apple M1 Ultra?
Written by Jakub Rusinowski · Last updated August 15, 2026
Yes, comfortably — GPT-OSS 120B at Q4_K_M needs 71.9 GB at 8K context (70.5 GB weights + 1.4 GB KV cache/overhead), leaving ~24.1 GB of the Apple M1 Ultra's 96 GB usable memory, at ~93 tok/s (est.), with room for up to 128K context.
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Apple M1 Ultra Specs
| VRAM | 128 GB unified memory |
| Memory Bandwidth | 800 GB/s |
GPT-OSS 120B on the Apple M1 Ultra: 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 M1 Ultra: 8K 71.9 GB · 32K 73.7 GB · 128K 81 GB. Every window this model publishes still fits 128 GB.
No compatible GPU? GPT-OSS 120B on 96 GB of system RAM, CPU only: runs, but it is tight.
GPT-OSS Sizes That Fit the Apple M1 Ultra (at 8K context)
| GPT-OSS 120B | Q4_K_M · 71.9 GB at 8K context · ~93 tok/s (est.) |
| GPT-OSS 20B | MXFP4 · 12.3 GB at 8K context · ~128 tok/s (est.) |
GPT-OSS 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.
FAQ
GPT-OSS on the Apple M1 Ultra — does it fit?
Yes, comfortably — GPT-OSS 120B at Q4_K_M needs 71.9 GB at 8K context (70.5 GB weights + 1.4 GB KV cache/overhead), leaving ~24.1 GB of the Apple M1 Ultra's 96 GB usable memory, at ~93 tok/s (est.), with room for up to 128K context.
Which GPT-OSS variant fits best on the Apple M1 Ultra?
GPT-OSS 120B at Q4_K_M quantization needs 71.9 GB at 8K context (70.5 GB weights + 1.4 GB KV cache/overhead), estimated ~93 tokens/sec, up to 128K context.
Every GPT-OSS size on the Apple M1 Ultra
| Size | VRAM at 8K | Verdict | Speed |
|---|---|---|---|
| GPT-OSS 120B | 71.9 GB | Runs | ~93 tok/s |
| GPT-OSS 20B | 12.3 GB | Runs | ~128 tok/s |
GPT-OSS on Other GPUs
- GPT-OSS on Apple M4 Max
- GPT-OSS on Apple M5 Max
- GPT-OSS on NVIDIA DGX Spark
- GPT-OSS on AMD Ryzen AI Max+ 395
Popular Models on the Apple M1 Ultra
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