Does Qwen3.8 Flash Next fit on a Mac Studio M5 Max 128 GB?

Yes. At MLX 4-bit it needs about 103 GB including the KV cache and runtime overhead, against roughly 109 GB usable — a borderline fit.

How fast is Qwen3.8 Flash Next on a Mac Studio M5 Max 128 GB?

We estimate ~97.9–141 t/s of decode throughput. This is calculated from memory bandwidth and active parameter count, not measured, so it is shown as a range.

What does it cost to run Qwen3.8 Flash Next on a Mac Studio M5 Max 128 GB?

The default US federal estimate is about $45 per month as a C corporation at 8 hours a day, including depreciation, electricity and tax relief, or roughly $2.99 per million output tokens at 20% generation utilisation. Use the selector for an interactive country estimate.

Qwen3.8 Flash Next on Mac Studio M5 Max 128 GB

180B (6B active) on 128 GB at 614 GB/s. Hardware details · Model details

Country

Buyer

Usage

CompatibilityBorderline

Fits

Yes

Calculated Uses 90-97% of usable memory. Likely to load but fragile under load or long context.

Recommended quantization

MLX 4-bit

Calculated mlx

Memory required

102.8 GB

Calculated of 108.8 GB usable — 94%

Max practical context

Calculated model supports 256K

Memory budget at 8K context

Model weights ⓘ

98.1 GB Calculated

KV cache ⓘ

0.8 GB Calculated

Runtime overhead ⓘ

3.9 GB Estimated

Total required

102.8 GB Calculated

Usable memory ⓘ

108.8 GB Assumption

Headroom

6.0 GB Calculated

Only a borderline fit (94% of usable memory). Expect to run headless and keep the context short.

Unified memory: weights, KV cache and the OS share the same 128 GB pool. We assume 85% is addressable by the GPU, which matches a headless machine with the wired-memory limit raised.

Mixture of experts: all 180B parameters must be resident in memory even though only ~6B are active per token. Memory follows total parameters; speed follows active parameters.

Borderline fit. It may load, but you will have little room for a longer context, a second process, or a desktop session.

PerformanceEstimated0/10

Decode (generation)

~97.9–141 t/s

Estimated calculated, not measured

Prefill (prompt)

~442–917 t/s

Estimated

TTFT at 8K

~9.0–18.7 s

Estimated time to first token

Power while generating

122 W

Measured 3.87 tokens/s per watt

These figures are estimated, not measured. Nobody has published a benchmark of Qwen3.8 Flash Next on this machine that we know of, so we calculate throughput from memory bandwidth and active parameter count. Estimates are always shown as a range. Expand the working below to see exactly how the number was produced.

How the estimate is calculated

Decode: reading 6.0B active parameters at 4.50 bits/weight takes 6.27 ms at 614 GB/s x 88% achieved efficiency.
MoE routing penalty of 15% applied: expert gathers are less bandwidth-efficient than a dense sweep.
Prefill: 120 TFLOPS (FP16) x 1.69 calibrated against measured prefill on this platform x 22% assumed model-FLOPs utilisation, divided by 2 x 32.9B parameters per token.
Prefill uses 32.9B effective parameters, not the 6B active in decode: a batch of hundreds of tokens routes across most of the expert pool.

MoE decode depends on how well the engine batches expert gathers; real results vary more than for dense models.
Prefill throughput is highly engine-dependent. Flash attention, batch size and quantized KV all move this number substantially, and for sparse mixture-of-experts models it is the least reliable figure we produce.
This is a calculated estimate, not a measurement. It assumes a single request, a short prompt, no speculative decoding and a warm model already resident in memory.

Estimator version estimator_v1. Stored with every estimated row so old estimates can be regenerated when the model improves.

This model at other quantizations on this machine

Quantization	Weights	Total needed	Utilisation	Fit
`MLX 4-bit`recommended	98.1 GB	102.8 GB	94%	Borderline
`Q4_K_M`	104.7 GB	109.6 GB	101%	Does not fit
`Q8_0`	181.7 GB	188.9 GB	174%	Does not fit
`BF16`	335.3 GB	347.1 GB	319%	Does not fit

Cost of running Qwen3.8 Flash Next on this machineUnited States (federal) · C corporation · 8h/day

Monthly economic cost

$45

Calculated after tax

Codex/Claude Code

$100/mo

≈ $100/mo · local is $55 less

Net cash at purchase

$4,323

Calculated VAT not reclaimable

Total over 5 years

$2,716

Calculated after tax, after resale

Cost per USD/1M tokens

$2.99

Calculated 15.1M tokens/month

The $100 comparison uses the Codex Pro 5x / Claude Max 5x plans. A fixed planning conversion is used for USD. This compares monthly spend only: subscriptions have usage limits, local hardware has different capabilities and constraints, and taxes or regional pricing may change the charged amount. Prices checked 7 September 2026.

Monthly breakdown

Depreciation 3,026 over 5 years, straight-line to a 1,297 residual	$50.44
Electricity 5.4 kWh/month at 0.140/kWh	$0.76
Cost of capital 4.0%/yr on 2,810 average capital employed	$9.37
Monthly cost before tax	$60.56
Electricity tax shield Running costs are deductible business expenses	−$0.16
First-year expensing §179 (100.0%)	−$15.13
Monthly economic cost after tax	$45.27

Three different numbers, deliberately

Cash cost

$4,323

Money that leaves the bank account on day one, net of reclaimable VAT.

Accounting depreciation

$50.44/month

$3,026 written down over 5 years to a $1,297 residual.

After-tax economic cost

$45.27/month

Depreciation plus running costs plus cost of capital, less the tax those deductions save. This is the figure to compare between machines.

Assumptions and sources (verified 2026-09-07)

VAT rate

0% Official spec

VAT recoverable

0% Official spec

Federal C-corporation estimate at the flat 21% rate. Pass-through entities should use the sole-proprietor estimate as a rougher proxy.

Effective deduction rate

21.00% Calculated

Headline marginal rate 21.00%.

Depreciation

5 years, straight-line Assumption

Residual value

$1,297 (30%) Assumption

Extrapolated from the three-year curve.

Electricity

$0.140/kWh Assumption

Average power draw

31 W Calculated

Load 122 W for 20% of powered hours, idle 8 W for the rest — a machine that is on is not generating tokens the whole time.

Investment allowances

§179 100.0% Official spec

Worth $908 in total — first-year expensing that replaces later tax depreciation.

Cost of capital

$9.37/month Assumption

VAT rate: No US federal VAT · verified 2026-09-07
Marginal tax rate: IRS Publication 542 — Corporations · verified 2026-09-07
VAT recoverable fraction: site assumption · verified 2026-09-07
Useful life: IRS Publication 946 — How To Depreciate Property · verified 2026-09-07
Electricity price: Site assumption · verified 2026-09-07

Assumes the machine generates tokens 20% of its 176 powered hours per month. Cost per token scales inversely with this number — halve the utilisation and the cost per token doubles.

Federal planning estimate only, not tax advice. State and local income tax, sales/use tax and incentives are excluded. It assumes 100% business use, a Section 179 election, enough business income to use it, and that the full annual limit remains available.

Efficiency metrics

Decode per $1,000 spent

27.6 t/s

Calculated purchase price only

Decode per $100/month

263.6 t/s

Calculated after-tax ownership cost

Tokens per joule

3.87

Calculated same as tokens/s per watt

USD per 1M output tokens

$2.99

Calculated at 20% utilisation

Local versus hosted APIs

Hosted model	USD/1M output	Break-even	API at your volume	Verdict	Comparison type
Qwen3.8 Flash Alibaba Cloud	$0.42	29.4M/mo	$23	API cheaper	Different model
DeepSeek-V4 Flash DeepSeek	$0.66	18.7M/mo	$37	API cheaper	Different model
DeepSeek-V4 Pro DeepSeek	$1.98	6.2M/mo	$110	Local cheaper	Different model
DeepSeek V4 Pro (Together) Together AI	$4.40	2.1M/mo	$321	Local cheaper	Different model
GLM-5.3 Z.ai	$4.40	2.9M/mo	$236	Local cheaper	Different model
Claude Haiku 4.5 Anthropic	$5.00	3.5M/mo	$197	Local cheaper	Different model

Different-model comparison: the hosted model is not the model you would run locally. Treat this as a workload-quality trade-off, not a direct economic equivalence — the frontier model may complete a task in fewer tokens, or complete tasks the local model cannot. Break-even is the monthly output volume at which API spend equals the $45/month economic cost of owning this machine, assuming 8 input tokens per output token. Hosted prices are published in USD. This table is the canonical US default.

Qwen3.8 Flash Next on other hardware

Hardware	Decode	Price	Fit
Quad RTX 5090 workstation (4x 32 GB)	~307–442 t/s	€13.999	Borderline
Mac Studio M5 Ultra 256 GB	~162–233 t/s	€9.599	Comfortable
Mac Studio M5 Ultra 512 GB	~101–145 t/s	€12.599	Comfortable
Mac Studio M3 Ultra 256 GB	~97.9–141 t/s	€6.299	Comfortable
Mac Studio M3 Ultra 512 GB	~58.9–84.7 t/s	€9.199	Comfortable
CPU-only workstation (Ryzen 9950X, 192 GB DDR5)	~8.5–12.3 t/s	€1.699	Comfortable

Nearest alternatives to the Mac Studio M5 Max 128 GB

Qwen3.8 Flash Next on Mac Studio M5 Ultra 96 GB96 GB Qwen3.8 Flash Next on Mac Studio M5 Max 64 GB64 GB Qwen3.8 Flash Next on Mac Studio M5 Ultra 256 GB256 GB Qwen3.8 Flash Next on Mac Studio M5 Max 36 GB36 GB Qwen3.8 Flash Next on Mac Studio M5 Ultra 512 GB512 GB

Compare Mac Studio M5 Max 128 GB against Mac Studio M5 Ultra 96 GB →

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Has a memory-fit calculation (+3)
Has a performance estimate (+2)
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Has an ownership economics calculation (+2)
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