Calculated with the 2026-09-28 rate of 1,356.04 KRW/USD (open.er-api), KEPCO’s residential low-voltage tariff (120.0 / 214.6 / 307.3 KRW/kWh tiered), and Claude’s official price list (Haiku 4.5 $1/$5, Sonnet 5 $2/$10 — a hike was planned for Sept 1 but $2/$10 is still the standard price). For local I assume a used 4090 (3.56M KRW) depreciated over 24 months + 70W system idle + 350W decode increment, aggregate 1,100 tok/s (gigagpu measured 3.4 tok/J).

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Monthly usage (output/input)	Electricity for local 4090 rigs	Local total/month	Haiku 4.5 API	Sonnet 5 API
Light users	2M / 10M	5,481 + depreciation 148,333 = ₩153,815	27,121 KRW	54,242 won
Intermediate user	8M / 40M	5,545 + depreciation 148,333 = 153,878 KRW	₩108,483	216,966 KRW
Heavy agents	20M / 100M	5,672 + depreciation 148,333 = 154,005 won	271,208 won	₩542,416

Interpretation

• Electricity always wins — even heavy users stay under 20,000 won/month. The real cost is card depreciation.
• Even including depreciation, at 8M output tok/month local matches Haiku; at 20M local is 2.7x cheaper. Break-even is roughly 7~8M output tok/month.
• If you want Sonnet 5-class quality, it’s a different story — to run that class locally you need Flash-Next 125B (M5 Max 128GB) class, where the machine cost lands before the electricity bill.
• bestllmfor’s aggregation points the same way: for agent workloads the break-even vs Haiku is 800,000–2,000,000 tokens of daily output.

The card’s own token unit costUsed 3090 unit-price table, model selection isHubat .

Written 2026-09-28 · file sizes measured from live Hugging Face listings · speeds only from sourced public measurements and my own · no local runs ·View the full hub · Quantization ladder, 104 builds · Generation-speed chart, 47 models