# What a model upgrade does to an unchanged workload > A model upgrade cost increase is the same workload at a different rate, and it can happen without you changing anything. Worked math inside. URL: https://getculpa.com/model-upgrade-cost-increase Last reviewed: 2026-08-01 Rates effective: 2026-07-02 ## Answer A model upgrade cost increase is the same workload priced at a new rate, and it happens whether or not you changed anything. Claude Sonnet 5's introductory pricing ends on 2026-09-01 and rises 50%. Culpa, a local-first LLM cost, margin, and forecast ledger, prices every call from a dated price book, so a rate change lands as a forecast rather than as an invoice. ## Why this happens Two different events get called a model upgrade. One is a decision: you move traffic to a newer model and accept a different rate. The other is a schedule: the rate on the model you already run changes on a date the provider set. Both produce the same arithmetic and only the first appears in anybody's plan. Because rate changes are dated, they're the one class of cost increase that's entirely forecastable in advance, and they're still the one that surprises teams most. ## What this usually looks like - A dated rate change is approaching on a model you run and nothing in your forecast reflects it. - A model migration was decided on quality alone, with cost checked afterwards. - Your cost model holds one rate per model rather than a rate with an effective date. - Nobody knows which models in production have a scheduled price change. ## Common mistakes - Holding one rate per model in your cost model. Why it hurts: A model can carry several rates over time, so a single rate silently mis-prices every period but one. Do instead: Store rates with effective dates and price each call at the rate in force when it was made. - Migrating models on quality alone. Why it hurts: A frontier model at five times the rate can cost more than the whole feature earns. Do instead: Price your actual monthly volume at both rates before the migration, then decide with both numbers. - Treating an introductory rate as the real one. Why it hurts: Introductory pricing has an end date, so a forecast built on it under-reads from that date onward. Do instead: Forecast at the post-introductory rate, and treat the discount as a temporary saving rather than a baseline. ## Self-check - List every model in production and check whether any carries a dated rate change. - Reprice last month's volume at the new rate. That difference is already scheduled. - Confirm your cost model prices calls by the rate in force on the call date rather than by today's rate. - For any migration under discussion, compute the same workload on both models before the quality debate. - Check what the same workload would cost on the tier below, so the upgrade has something to be compared against. ## One workload, four rates (illustrative) A monthly workload of 900 million input tokens and 140 million output tokens. All four rates below are real price book rows, quoted per million. The volumes are modelled. Claude Sonnet 5 at introductory rates: (900 x $2.00) + (140 x $10.00) = $1,800 + $1,400 = $3,200 Claude Sonnet 5 from 2026-09-01: (900 x $3.00) + (140 x $15.00) = $2,700 + $2,100 = $4,800 The same workload on Claude Opus 4.8: (900 x $5.00) + (140 x $25.00) = $4,500 + $3,500 = $8,000 The same workload on Claude Haiku 4.5: (900 x $1.00) + (140 x $5.00) = $900 + $700 = $1,600 The September increase is $1,600 a month, which is exactly what the entire workload would cost on Haiku 4.5 A 50% rise arrives on a known date with nobody deciding anything. The increase alone equals the full cost of running the same work on the tier below, which makes the September date a decision point rather than an event. ## Cost figures Every figure carries its confidence and its source. No figure on this site is provider-reported. - $3,200 to $4,800 — modelled monthly cost of one unchanged workload on Claude Sonnet 5, before and after 2026-09-01 [estimated] Source: Both endpoints use real Claude Sonnet 5 rows from the price book, $2.00 and $10.00 per million effective 2026-07-02 and $3.00 and $15.00 effective 2026-09-01. A range because the token volumes are modelled. - $1,600 — modelled monthly increase from the scheduled Sonnet 5 rate change, at unchanged volume [calculated] Source: $4,800 minus $3,200, from the teardown arithmetic at real price book rates. ## FAQ Q: When does Claude Sonnet 5 pricing change? A: On 2026-09-01. Anthropic's pricing page states that introductory pricing of $2 and $10 per million input and output runs through August 31, 2026, after which standard pricing of $3 and $15 per million takes effect, a 50% rise. Q: How do I forecast a dated rate change? A: Take last month's token volumes for that model and multiply by both rates. The difference is your scheduled increase, and because it's dated rather than probabilistic it belongs in the budget rather than in a risk register. Q: Is upgrading to a newer model usually cheaper? A: Not reliably. Newer models sometimes launch below the ones they replace and sometimes above, and introductory rates expire. The only dependable method is pricing your own volumes at both rates, because the direction changes model by model. ## Sources - Anthropic pricing: https://platform.claude.com/docs/en/docs/about-claude/pricing Run the free Cost Leak Scan: https://app.getculpa.com/scan?source=pseo&slug=model-upgrade-cost-increase&cluster=problem Machine-readable index of every guide: https://getculpa.com/api/pages Human-readable index of every guide: https://getculpa.com/guides Site overview: https://app.getculpa.com/llms.txt Privacy: Culpa runs on your infrastructure. Your prompts and responses never leave it. Culpa counts calls to run your plan, and it fails open, so if it ever breaks your app keeps running.