gpt-oss-20b on Mac Studio M1 Max 64 GB
20.915B (3.6B active) on 64 GB at 400 GB/s. Hardware details · Model details
Yes. gpt-oss-20b fits on Mac Studio M1 Max 64 GB at the recommended
MXFP4 configuration, requiring approximately 13.0 GB at 8K context. Practical context capacity is 128K.CompatibilityComfortable
Calculated fit
Yes
Calculated Uses under 80% of usable memory. Room for a long context and other work.
Recommended quantization
MXFP4
Calculated gguf
Memory required
13.0 GB
Calculated of 54.4 GB usable — 24%
Max practical context
128K
Calculated model supports 128K
Memory budget at 8K context
Model weights ⓘ
11.3 GB Calculated
KV cache ⓘ
0.4 GB Calculated
Runtime overhead ⓘ
1.3 GB Estimated
Total required
13.0 GB Calculated
Headroom ⓘ
41.4 GB Calculated
Highest-precision quantization that leaves headroom: uses 24% of usable memory at 8K context.
Unified memory: weights, KV cache and the OS share the same 64 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 20.915B parameters must be resident in memory even though only ~3.6B are active per token. Memory follows total parameters; speed follows active parameters.
Performance
Estimated performance · recommended MXFP4
Decode, prefill and TTFT below are estimates for MXFP4. We do not have a comparable MXFP4 measurement on this machine.
Estimated decode
—
Estimated MXFP4; calculated range
Estimated prefill
—
Estimated MXFP4; calculated range
Estimated TTFT at 8K
—
Estimated MXFP4; calculated range
Hardware load reference
—
Official spec hardware TDP; not this model run
No throughput figures for this configuration. We do not estimate performance for a model that cannot load.
How the estimate is calculated
- Decode: reading 3.6B active parameters at 4.25 bits/weight takes 6.83 ms at 400 GB/s x 70% achieved efficiency.
- MoE routing penalty of 15% applied: expert gathers are less bandwidth-efficient than a dense sweep.
- MoE decode depends on how well the engine batches expert gathers; real results vary more than for dense models.
- No FP16 compute figure for this hardware, so prefill cannot be estimated.
- 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.
Submit a benchmarkSubmissions stay pending until reviewed.
This model at other quantizations on this machine
| Quantization | Resident | Disk | Total needed | Utilisation | Fit | Max context |
|---|---|---|---|---|---|---|
MXFP4recommended | 11.3 GB | 11.3 GB | 13.0 GB | 24% | Comfortable | 128K |
BF16 | 39.0 GB | 39.0 GB | 41.5 GB | 76% | Comfortable | 128K |
Cost of running gpt-oss-20b on this machineUnited States (federal) · C corporation · 8h/day
Monthly economic cost
$0
Calculated after tax
Codex/Claude Code
$100/mo
≈ $100/mo · local is $100 less
Net cash at purchase
$0
Calculated VAT not reclaimable
Total over 5 years
$0
Calculated after tax, after resale
Cost per USD/1M tokens
—
Calculated
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 0 over 5 years, straight-line to a 0 residual | $0.00 |
| Electricity 0.0 kWh/month at 0.140/kWh | $0.00 |
| Monthly cost before tax | $0.00 |
| Electricity tax shield Running costs are deductible business expenses | -$0.00 |
| Monthly economic cost after tax | $0.00 |
Three different numbers, deliberately
Cash cost
$0
Money that leaves the bank account on day one, net of reclaimable VAT.
Accounting depreciation
$0.00/month
$0 written down over 5 years to a $0 residual.
After-tax economic cost
$0.00/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
$0 (30%) Assumption
Extrapolated from the three-year curve.
Electricity
$0.000/kWh Assumption
Average power draw
0 W Calculated
Load — for 20% of powered hours, idle 0 W for the rest — a machine that is on is not generating tokens the whole time.
Investment allowances
§179 100.0% Official spec
Worth $0 in total — first-year expensing that replaces later tax depreciation.
Cost of capital
not applied 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
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.
gpt-oss-20b on other hardware
| Hardware | Decode | Price | Fit |
|---|---|---|---|
| NVIDIA DGX H200 (8x H200, 1,128 GB) | ~553–796 t/s | $359,430 * | Comfortable |
| Quad RTX 5090 workstation (4x 32 GB) | ~387–556 t/s | $12,611 * | Comfortable |
| Lenovo ThinkStation PX (4x RTX PRO 6000, 384 GB) | ~366–527 t/s | $58,553 * | Comfortable |
| RTX 5090 workstation (1x 32 GB) | 419 t/s | $3,332 * | Comfortable |
| RTX PRO 6000 Blackwell workstation (96 GB) | ~329–474 t/s | $10,359 * | Comfortable |
| RTX PRO 6000 Max-Q workstation (96 GB, 300 W) | ~329–474 t/s | $10,809 * | Comfortable |
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