# Claude Sonnet 5 pricing, and the rate change on 2026-09-01

> Claude Sonnet 5 pricing is $2.00 per million input and $10.00 output on an introductory rate that ends 2026-08-31, rising 50% to $3.00 and $15.00.

URL: https://getculpa.com/claude-sonnet-5-pricing
Last reviewed: 2026-08-01
Rates effective: 2026-07-02

## Answer
Claude Sonnet 5 pricing is $2.00 per million input tokens and $10.00 per million output tokens on an introductory rate. From 2026-09-01 it rises to $3.00 and $15.00, a 50% increase on both sides. Culpa, a local-first LLM cost, margin, and forecast ledger, holds dated rates, so a forecast built today prices September correctly.

## Why this happens
Sonnet 5 is the only model in this price book carrying two rate rows with different effective dates. That makes it the clearest example of why a price book needs versions rather than a single current number. Any forecast built on today's $2.00 rate under-reads September by a third, and any attempt to re-price August's history at the September rate rewrites the past. Both failures are silent.

## What this usually looks like
- Your September forecast was built on the August rate and nobody flagged the change.
- Historical cost reports shift when re-run, because the pricing lookup uses the current rate rather than the dated one.
- The budget for a Sonnet 5 feature was signed off against introductory pricing with no end date noted.
- Nobody can say which rate a given month's spend was calculated at.

## Common mistakes
- Forecasting September at the introductory rate. Why it hurts: The forecast under-reads by a third, and the miss lands in the first month anyone checks. Do instead: Price forward at $3.00 and $15.00 from 2026-09-01, and say in the forecast which rate each month used.
- Re-pricing historical calls at the current rate. Why it hurts: It rewrites months that were genuinely cheaper, so trend analysis becomes meaningless. Do instead: Price every call at the rate in effect on its own date, and keep the effective date on the record.
- Assuming an introductory rate is permanent because nothing announced its end. Why it hurts: The end date exists in the price book already, so the increase is scheduled rather than a surprise. Do instead: Check the effective dates on every rate you depend on, and diary the ones that change.

## Self-check
- Confirm which rate your cost system uses for August spend and which it will use for September.
- Re-run a month-old report and check the total still matches. A shift means dated pricing isn't in place.
- Price your current Sonnet 5 volume at $3.00 and $15.00. That's your September bill at flat usage.
- Check whether any budget or customer quote was built on the introductory rate.
- Look at whether Sonnet 4.6 is now the same price as Sonnet 5 will be, and whether that changes your choice.

## The same usage, priced either side of 2026-09-01 (illustrative)
A production feature sending 20 million input and 4 million output tokens a month, unchanged across the rate boundary. Both rates come from the same model's two price-book rows.
  August, introductory: (20 x $2.00) + (4 x $10.00) = $40.00 + $40.00 = $80.00
  September, standard: (20 x $3.00) + (4 x $15.00) = $60.00 + $60.00 = $120.00
  Increase = $40.00 a month, or 50%, with no change in usage at all
  Cached input also moves, $0.20 to $0.30 per million
  A twelve-month budget signed at the August rate under-reads by $480 on this volume
A 50% increase arrives on 2026-09-01 with no usage change and no action on your side. It's in the price book today, so there's no excuse for it to surprise a forecast.

## Cost figures
Every figure carries its confidence and its source. No figure on this site is provider-reported.
- $2.00 / $10.00 per million — Claude Sonnet 5 introductory input and output rates, effective 2026-07-02 [calculated] Source: Culpa price book row for anthropic/claude-sonnet-5, $0.002 and $0.010 per 1k, effective 2026-07-02, verified against Anthropic pricing.
- $3.00 / $15.00 per million — Claude Sonnet 5 standard rates, effective 2026-09-01 [calculated] Source: Second price book row for anthropic/claude-sonnet-5, $0.003 and $0.015 per 1k, effective 2026-09-01.
- 50% — rate increase on both input and output at the 2026-09-01 boundary [calculated] Source: ($3.00 - $2.00) / $2.00, and ($15.00 - $10.00) / $10.00, from the two dated rows above.

## FAQ
Q: When does Claude Sonnet 5 introductory pricing end?
A: The price book carries the introductory rate from 2026-07-02 and a standard rate effective 2026-09-01, so the introductory period runs through 2026-08-31. Verify against Anthropic's pricing page before committing a budget to it.

Q: How much does the Sonnet 5 rate change cost me?
A: 50% on both input and output, from $2.00 and $10.00 to $3.00 and $15.00 per million. At 20 million input and 4 million output tokens a month that's $40 more, with no usage change.

Q: Should I re-price old months at the new rate?
A: No. Price every call at the rate in effect on its own date. Re-pricing history at a current rate makes cheaper months look expensive and destroys any trend you were trying to read.

## Sources
- Anthropic pricing: https://platform.claude.com/docs/en/docs/about-claude/pricing

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