How fast is DeepSeek V4.1 Flash on an Mac?

Around 1 tokens per second. Token generation on Apple Silicon is limited by memory bandwidth, and this machine has 819 GB/s.

How much memory does DeepSeek V4.1 Flash need?

435.4 GiB for the weights at Q4_K_M, plus 0.6 GiB for an 8K-token KV cache and about 22.6 GiB of runtime overhead — 458.6 GiB in total.

Home › DeepSeek V4.1 Flash › M3 Ultra 512GB

Can an M3 Ultra 512GB Mac run DeepSeek V4.1 Flash?

M3 Ultra · 512 GB unified memory · 819 GB/s · Mac Studio (M3 Ultra)

Just barely — and you will feel it.

DeepSeek V4.1 Flash at Q4_K_M needs about 458.6 GiB against roughly 496.0 GiB usable — that is 92% of your budget. It will load, but close your browser first, keep the context short, and expect memory pressure. Around 1 tokens/sec.

Weights

435.4 GiB

763.21B params @ Q4_K_M

KV cache

0.6 GiB

8K context, FP16

Overhead

22.6 GiB

runtime + activations

Total needed

458.6 GiB

of ~496.0 GiB usable

Est. speed

1 tok/s

819 GB/s bandwidth

Max context

128K tokens

at Q4_K_M

Where the memory goes

Three things occupy memory when a model is loaded: the weights themselves, the KV cache that holds the conversation, and the runtime's own working buffers. Only the first is fixed — the KV cache grows with every token in your context.

Quantisation	Weights	Total	Tok/s	Fits?
FP16	1421.6 GiB	1494.1 GiB	0	No
Q8_0	755.2 GiB	794.4 GiB	1	No
Q6_K	586.4 GiB	617.2 GiB	1	No
Q5_K_M	506.4 GiB	533.2 GiB	1	No
Q4_K_M	435.4 GiB	458.6 GiB	1	Yes, but tight
Q3_K_M	346.5 GiB	365.3 GiB	2	Yes, comfortably
Q2_K	266.5 GiB	281.3 GiB	2	Yes, comfortably

The default. Best quality-per-gigabyte for most people.

How long a context fits

The KV cache is often what breaks a setup that looked fine at load time. Quantising it to 8-bit roughly halves its footprint with little measurable quality cost.

Context	KV cache	Total	FP16 KV	Q8 KV
2K	0.2 GiB	457.9 GiB	Yes, but tight	Yes, but tight
4K	0.3 GiB	458.1 GiB	Yes, but tight	Yes, but tight
8K	0.6 GiB	458.6 GiB	Yes, but tight	Yes, but tight
16K	1.3 GiB	459.5 GiB	Yes, but tight	Yes, but tight
32K	2.5 GiB	461.3 GiB	Yes, but tight	Yes, but tight
128K	10.0 GiB	472.4 GiB	Yes, but tight	Yes, but tight

What to run instead on an M3 Ultra 512GB Mac

These are the largest models that fit comfortably on this machine at Q4_K_M with an 8K context.

Model	Size	Total	Tok/s
DeepSeek R1	684.49B	411.3 GiB	18	Yes, comfortably
Llama 3.1 405B	405B	247.3 GiB	3	Yes, comfortably
DeepSeek V4 Flash Vision Exp	304.65B	183.9 GiB	4	Yes, comfortably
DeepSeek V4 Flash 0731	304.18B	183.7 GiB	4	Yes, comfortably
DeepSeek V4 Flash	290.94B	175.7 GiB	4	Yes, comfortably
gpt-oss-120b	116.8B	71.3 GiB	131	Yes, comfortably

How to run it

Ollama is the shortest path. It picks a quantisation automatically — usually Q4_K_M, which is what the numbers above assume.

brew install ollama
ollama serve &
ollama run deepseek-v4-1-flash

For MLX — Apple's own array framework, typically a little faster than llama.cpp on Apple Silicon:

pip install mlx-lm
mlx_lm.generate --model mlx-community/DeepSeek-V4-1-Flash-4bit --prompt "Hello"

You are close to the limitIf it stutters or gets killed, raise the Metal memory cap before loading: sudo sysctl iogpu.wired_limit_mb=445644. This resets on reboot. Quantising the KV cache (--kv-cache-type q8_0 in llama.cpp) buys back 0.3 GiB.

Macs that run DeepSeek V4.1 Flash

No Apple Silicon configuration in our list runs DeepSeek V4.1 Flash comfortably at Q4_K_M with an 8K context. This one needs a multi-GPU server.

Common questions

Can an M3 Ultra 512GB Mac run DeepSeek V4.1 Flash?: Yes. At Q4_K_M it needs about 458.6 GiB of the roughly 496.0 GiB available, generating around 1 tokens per second.
How fast is DeepSeek V4.1 Flash on an Mac?: Around 1 tokens per second. Token generation on Apple Silicon is limited by memory bandwidth, and this machine has 819 GB/s.
How much memory does DeepSeek V4.1 Flash need?: 435.4 GiB for the weights at Q4_K_M, plus 0.6 GiB for an 8K-token KV cache and about 22.6 GiB of runtime overhead — 458.6 GiB in total.