Can I Run GPT-OSS 20B on Apple M1?
Written by Jakub Rusinowski · Last updated August 15, 2026
Not at MXFP4 — that needs 12.3 GB at 8K context and the Apple M1 has 12 GB usable. Drop to Q3_K_M and it fits in 10.1 GB, with up to 32K of context.
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The numbers
| Model | GPT-OSS 20B |
| Parameters | 20B |
| Quantization | MXFP4 |
| VRAM needed (8K context) | 12.3 GB |
| Apple M1 usable memory | 12 GB |
| Verdict | Runs at a lower quant |
| Fits at | Q3_K_M (10.1 GB) |
| Max context | 32K |
GPT-OSS 20B on the Apple M1: VRAM by quantization
| Quant | VRAM needed | Fits 16 GB? | Max context | Whole PC |
|---|---|---|---|---|
| F16 | 43 GB | ✗ No | — | — |
| Q8_0 | 23.4 GB | ✗ No | — | — |
| Q6_K | 18.3 GB | ✗ No | — | — |
| Q5_K_M | 16 GB | ✗ No | — | — |
| Q4_K_M | 13.8 GB | ✗ No | — | — |
| Q3_K_M | 10.1 GB | ✓ Yes | 32K | — |
| Q2_K | 8.1 GB | ✓ Yes | 64K | — |
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 16 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 MXFP4 on the Apple M1: 8K 12.3 GB ✗ · 32K 13.5 GB ✗ · 128K 18.3 GB ✗. Past 8K it no longer fits 16 GB — a q8_0 KV cache buys roughly half of that back, which the calculator will price for you.
What to do next
Quantize to Q3_K_M. That is the cheapest fix — it costs some quality but no money.
No compatible GPU? GPT-OSS 20B on 16 GB of system RAM, CPU only: runs.
Running GPT-OSS 20B on this card:
GPT-OSS 20B needs ~12 GB but this GPU has 16 GB. Rent a RTX 4090 (24 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 M1
- GPT-OSS 120B — does not fit (71.9 GB)
GPT-OSS 20B on nearby hardware
- Intel Arc B580 (12 GB) — runs at a lower quant
- AMD Radeon RX 7900 XT (20 GB) — runs
All GPT-OSS sizes on the Apple M1 | GPT-OSS 20B model page | Apple M1 GPU page | VRAM calculator | Check your hardware