Is unified memory on Mac Studio M2 Ultra 64GB as fast as VRAM for Qwen3.5 397B A17B?

Not always. Mac Studio M2 Ultra 64GB can often fit larger models thanks to unified memory, but a discrete GPU with dedicated high-bandwidth VRAM may still decode faster once the model fits. For this combination, the important distinction is capacity versus sustained throughput.

Can Qwen3.5 397B A17B run on Mac Studio M2 Ultra 64GB?

Q: What should I upgrade first if Qwen3.5 397B A17B feels slow on Mac Studio M2 Ultra 64GB?

Move to a larger memory pool. A larger unified-memory SKU or a discrete high-bandwidth GPU is the cleanest way to make this model practical.

NO — Won't Fit

F0Won't run

Estimated from fit model

Qwen3.5 397B A17B needs ~296.5 GB but Mac Studio M2 Ultra 64GB only has 46.1 GB. Try a smaller quantization or lighter model.

Runtime: llama.cppCapacity: No fitBandwidth: HighStack: StandardBottleneck: Memory capacity

Operating mode

Choose the run profile you care about

Interactive favors responsiveness, while light API and scale-out lean harder on serving readiness. The fit stays the same, but the recommendation lens changes.

Current mode

Balanced

Balanced for general local use. Keeps the ranking neutral across personal and serving workflows.

Capabilities:

Select quantization to explore

Q4_K_M (Medium quality) — 296.5 GB, exceeds 46.1 GB available

296.5 GB required46.1 GB available

643% VRAM needed

250.4 GB over capacity — needs offload or smaller quantization

Fit status

Too heavy

Decode

2.0 tok/s

TTFT

96800 ms

Safe context

Memory

296.5 GB / 46.1 GB

Offload

80%

Memory breakdown

Weights242.2 GB

KV Cache46.5 GB

Runtime0.9 GB

Headroom6.9 GB

See how fast it feels

With memory offload — actual speed may be lower

See how fast it feelsQwen3.5 397B A17B on Mac Studio M2 Ultra 64GB
1st promptCold start — includes initialization
>What is local AI inference?
Local AI inference means running an AI language model directly on your own hardware — your laptop, desktop, or server — instead of sending requests to a remote cloud API.

When you run inference locally the model weights are loaded into your GPU or unified memory. Each token you generate requires reading those weights from memory, so memory bandwidth is the main bottleneck for decode speed.

Key benefits of running locally:
  - Full privacy: your prompts never leave your machine
  - No per-token cost or rate limits
  - Works offline once the model is downloaded
  - Latency depends only on your hardware
2nd promptWarm — model ready, no init overhead
>How much VRAM do I need?
It depends on the model size and quantization level. A rough rule of thumb:

  Model size     Q4 (4-bit)    Q8 (8-bit)    FP16
  7B params      ~4.3 GB       ~7.5 GB       ~14 GB
  13B params     ~7.9 GB       ~13.9 GB      ~26 GB
  70B params     ~42.7 GB      ~74.9 GB      ~140 GB

Most people use 4-bit quantization (Q4_K_M) which gives 90-95% of full quality at a fraction of the memory. A 24 GB GPU can comfortably run most 7B-13B models.
Estimated: 2.0 tok/s decode · 96.8s TTFT (warm) · 5 tok/s prefill

What limits this setup

Usable shared or unified memory is the main blocker for this model.

Not enough usable memory

The model needs 296.5 GB, but this setup only exposes 46.1 GB of usable shared or unified memory.

Best improvement path

Move to a larger memory pool

A larger unified-memory SKU or a discrete high-bandwidth GPU is the cleanest way to make this model practical.

Performance by workload

Workload	Grade	Fit	Decode	TTFT	Context
Chat	F	Too heavy	2.0 tok/s	52800 ms	4K
Coding	F	Too heavy	2.0 tok/s	96800 ms	4K
Agentic Coding	F	Too heavy	2.0 tok/s	140800 ms	4K
Reasoning	F	Too heavy	2.0 tok/s	114400 ms	4K
RAG	F	Too heavy	2.0 tok/s	176000 ms	4K

Quantization options

How Qwen3.5 397B A17B (397B params) fits at each quantization level on Mac Studio M2 Ultra 64GB (46.1 GB usable).

Quant	Bits	VRAM	Quality	Fit
Q2_K	2	154.8 GB	Low	F0
Q3_K_S	3	194.5 GB	Low	F0
NVFP4	4

Upgrade options

Hardware that runs Qwen3.5 397B A17B well

AMD Instinct MI350X 288GBBest value

288 GB VRAM (+224)8000 GB/s (+7200)

Makes the model fit on the accelerator instead of staying completely out of reach.14.6 tok/s decode

Makes the model fit on the accelerator instead of staying completely out of reach.

Raises estimated decode speed by about 630%.

~$8,000 MSRP

Frequently asked questions

Can Mac Studio M2 Ultra 64GB run Qwen3.5 397B A17B?

No, Qwen3.5 397B A17B requires more memory than Mac Studio M2 Ultra 64GB provides.

How much VRAM does Qwen3.5 397B A17B need?

Qwen3.5 397B A17B (397B parameters) requires approximately 296.5 GB of memory with Q4_K_M quantization.

What is the best quantization for Qwen3.5 397B A17B?

The recommended quantization for Qwen3.5 397B A17B is Q4_K_M, which balances quality and memory efficiency.

What speed will Qwen3.5 397B A17B run at on Mac Studio M2 Ultra 64GB?

On Mac Studio M2 Ultra 64GB, Qwen3.5 397B A17B achieves approximately 2.0 tokens per second decode speed with a time-to-first-token of 96800ms using Q4_K_M quantization.

Can Mac Studio M2 Ultra 64GB run Qwen3.5 397B A17B for coding?

For coding workloads, Qwen3.5 397B A17B on Mac Studio M2 Ultra 64GB receives a F grade with 2.0 tok/s and 4K context.

What context window can Qwen3.5 397B A17B use on Mac Studio M2 Ultra 64GB?

On Mac Studio M2 Ultra 64GB, Qwen3.5 397B A17B can safely use up to 4K tokens of context. The model's official context limit is —, but available memory constrains the safe maximum.

What should I upgrade first if Qwen3.5 397B A17B feels slow on Mac Studio M2 Ultra 64GB?

See all results for Mac Studio M2 Ultra 64GB See all hardware for Qwen3.5 397B A17B

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