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Yes. gpt-oss 20B (MoE, MXFP4) fits in fast memory on Mac Studio M3 Ultra (80c GPU) 256GB at MXFP4 (15.1 GB needed, 192.0 GB usable), about 136 tok/s (estimate).
Hardware: Mac Studio M3 Ultra (80c GPU) 256GB · Model: gpt-oss 20B (MoE, MXFP4)
Mac Studio M3 Ultra (80c GPU) 256GB has 256 GB of unified memory and 819 GB/s of memory bandwidth. Mac Studio M3 Ultra (60c GPU) 256GB has the same memory and bandwidth, so the fit numbers match; this page is Mac Studio M3 Ultra (80c GPU) 256GB. The checker leaves macOS a share of unified memory, so Ollama can use 192.0 GB. gpt-oss 20B (MoE, MXFP4) (20.9B, 3.6B active, OpenAI) at MXFP4 is a 14 GB download and needs 15.1 GB with headroom for about 8k tokens.
| Best quant | MXFP4 |
|---|---|
| Download size | 14 GB |
| Memory needed | 15.1 GB |
| Usable fast memory | 192.0 GB |
| Fit | fits in fast memory |
| Estimated speed | ~136 tok/s (estimate) |
| Command | ollama run gpt-oss:20b |
Estimates, not benchmarks. Model sizes are ollama.com download sizes; memory needed adds headroom for ~8k tokens of context; speeds are rough figures from memory bandwidth. Data updated 2026-10-23.
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