Apple128 GB VRAM546 GB/s$0/hr

GPT-NeoX 20B on Mac M4 Max (128GB): Does It Fit, How Fast, What It Costs

GPT-NeoX 20B at FP8 (E4M3) needs 20.0 GB for its weights and 90.9 GB in total at 8K context with 8 concurrent users. That means it fits on a single Mac M4 Max (128GB). Every figure is computed by tokcalc's open-source capacity model.

Fits?
Yes, 1 GPU
90.9 GB needed / 128 GB available
Decode speed
26.62
tok/s per stream
Aggregate
212.5
tok/s @ 8 concurrent
Cost / 1M tokens
—
1× Mac M4 Max (128GB) · quote required
What changes as you add Mac M4 Max (128GB)s
Tensor-parallel degree vs VRAM, throughput, and cost. Cost scales linearly with GPU count; decode throughput scales near-linearly too, so cost per token stays roughly flat.
GPUsTotal VRAMVRAM neededDecode tok/sAggregate tok/sTTFTCost / 1M tokFits?
1× Mac128 GB90.9 GB26.62212.538.62 s—✓
2× Mac256 GB90.9 GB45.25850.019.33 s—✓
4× Mac512 GB90.9 GB90.5034009.68 s—✓
8× Mac1024 GB90.9 GB181.0136004.85 s—✓
Concurrency vs context length
On 1× Mac M4 Max (128GB) at FP8 (E4M3). KV cache scales linearly with context, so this is the number of users your GPUs can actually serve.
ContextConcurrent usersKV per requestFits?
4K244.43 GB✓ fits
8K128.86 GB✓ fits
33K335.43 GB✓ fits
66K170.87 GB✓ fits
131K0141.73 GB✗ does not fit
Other GPUs that run GPT-NeoX 20B
Same workload, same quantization — ranked by value (tokens per dollar-hour).
GPUGPUsAggregate tok/sCost / 1M tok
RTX 5090 32GB4×14257$0.0390
A100 80GB SXM42×3978$0.1676
H100 SXM5 80GB2×6663$0.2084
AMD MI300X 192GB1×3101$0.2240
L40S 48GB2×1718$0.2263
AMD MI325X 288GB1×3510$0.2770
Frequently asked questions

Can GPT-NeoX 20B run on Mac M4 Max (128GB)?

Yes. GPT-NeoX 20B at FP8 (E4M3) needs 90.9 GB including the KV cache, and Mac M4 Max (128GB) has 128 GB — so it fits on a single GPU.

How fast is GPT-NeoX 20B on Mac M4 Max (128GB)?

26.62 tokens/sec per stream and 212.5 tok/s aggregate with continuous batching at 8 concurrent users. Time to first token is 38.62 s, and inter-token latency is 37.6 ms.

What does GPT-NeoX 20B on Mac M4 Max (128GB) cost per million tokens?

— per 1M output tokens at 1× Mac M4 Max (128GB). That is the marginal hardware cost — add idle capacity, ops, and egress for the real figure.

How much VRAM does GPT-NeoX 20B need on Mac M4 Max (128GB)?

20.0 GB for the weights at FP8 (E4M3), plus 70.9 GB of KV cache for 8 concurrent requests at 8K context — 90.9 GB total. Every extra concurrent user at long context costs more, so leave headroom.

Is Mac M4 Max (128GB) the right choice for GPT-NeoX 20B?

It works. Compare — per 1M tokens against the alternatives below — the cheapest option that fits the same workload is 8× RTX 4080 16GB at $0.0292, and the fastest is 4× Cerebras CS-3 (WSE-3) at 159120 tok/s.

Adjust the workload yourself

Same formulas, your context length, concurrency, and quantisation.

Open in calculator