Can I Run GLM-5.3-Flash on Mac Studio (M3 Ultra, 256 GB)?

Written by Jakub Rusinowski · Last updated September 11, 2026

Yes — comfortably

Yes, comfortably — GLM-5.3-Flash 320B-A18B at Q3_K_M needs about 141.2 GB of the 192 GB usable on Mac Studio (M3 Ultra, 256 GB), leaving ~50.8 GB spare and running at ~40.8 tok/s (estimated), with room for about 65,536 tokens of context.

Confidence: medium · Recommended quantization: Q3_K_M · Estimated speed: ~40.8 tok/s

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Mac Studio (M3 Ultra, 256 GB) — what it gives a model

Usable memory for models	192 GB
Memory bandwidth	819 GB/s
Form factor	Desktop
Operating system	macOS
Memory upgradeable	No — soldered

GLM-5.3-Flash on Mac Studio (M3 Ultra, 256 GB): memory by quantization

Quant	Memory needed	Fits 192 GB?	Max context	Est. speed	Download
F16	644.8 GB	✗ No	—	—	640 GB
Q8_0	344.8 GB	✗ No	—	—	340 GB
Q6_K	267.2 GB	✗ No	—	—	262.4 GB
Q5_K_M	231.6 GB	✗ No	—	—	226.8 GB
Q4_K_M	198 GB	✗ No	—	—	193.2 GB
Q3_K_M	141.2 GB	✓ Yes	64K	~40.8 tok/s	136.4 GB
Q2_K	110 GB	✓ Yes	128K	~48.6 tok/s	105.2 GB

What to watch out for

Q3_K_M is the only quantization that fits, and it is a heavily degraded one — expect noticeably worse output than the same model at Q4_K_M. A smaller model at Q4 is usually the better trade.
1 larger variant of GLM-5.3-Flash does not fit and would need CPU offload or different hardware.
This model does not publish its full attention configuration, so the KV-cache share of these figures is inferred from its parameter count rather than computed exactly.
Memory on this machine is not upgradeable, so the configuration you buy is the ceiling for every model you will ever run on it.

Mac Studio M3 Ultra 256 GB limitations

The largest single-box unified memory pool available, but at roughly half the memory bandwidth of a high-end discrete GPU — very large models load, then run slowly.
Memory is soldered; the configuration chosen at purchase is permanent.

Recommended setup

Ollama or LM Studio (Metal) — MLX for the fastest Apple-native throughput

How these numbers are calculated

Memory need = quantized weights + KV cache at 8,192 tokens (f16) + 0.8 GB runtime overhead.
256 GB unified memory at 819 GB/s, shared between CPU and GPU.
macOS reserves a share of unified memory for the system, so not all of it is available to a model.
Throughput is a memory-bandwidth roofline estimate, not a measurement. It is labelled "estimated" everywhere it appears.
KV cache is inferred from the parameter count because this model does not publish its full attention configuration.

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