News

Claude Sonnet 5's introductory price expires on 31 August — and the bill rises 50%

Anthropic's model documentation carries a footnote that is easy to miss and expensive to ignore: the introductory pricing of $2 per million input tokens and $10 per million output tokens applies to Claude Sonnet 5 only through 31 August 2026. From 1 September the model reverts to its list price of $3 and $15 — a 50% increase on both sides of the meter, arriving in under four weeks. Sonnet 5 is not a marginal product for Anthropic. Released on 30 June 2026, it is the default model for Claude's free and Pro users and the company's declared best combination of speed and intelligence, with a native one-million-token context window, 128,000 output tokens on the Messages API and 63.2% on SWE-Bench Pro. It is also, as of today, the only current Claude model sold below its own list price: Fable 5 stands at $10 / $50, Opus 5 at $5 / $25 and Haiku 4.5 at $1 / $5, all at list. There is a second, quieter movement in the same direction, and it has nothing to do with the price card. Anthropic's own documentation puts the one-million-token window of Fable 5, Opus 5 and Sonnet 5 at roughly 555,000 words, while the same one million tokens on Opus 4.6 and Sonnet 4.6 held about 750,000 words. For Fable 5 the company states the mechanism outright: it uses the tokenizer introduced with Opus 4.7, and the same text produces roughly 30% more tokens than on the older models. Since tokens are the billing unit, an unchanged workload on the newer generation is metered higher before any rate change is applied at all. What this does not appear to be is a repricing of the frontier. Anthropic has not announced a change to any other model's rates, and the retirement floor for Sonnet 5 remains unmoved at 30 June 2027. The plain reading is that a launch discount is simply running out on schedule. For anyone budgeting against Sonnet 5, the two dates that matter are 31 August, when the discount ends, and the moment a workload is ported from a 4.6-generation model, when the token count itself changes. Our Claude Sonnet 5 profile now carries both the introductory and the list price.