Opus 5.5 Is 20% Cheaper. The Other 20% Is Anthropic Asking You to Let It Think Less.
Anthropic's flagship price cut is real and checks out against its own price list. The "closer to 40%" savings number the company is showcasing three weeks before a roughly $2 trillion IPO roadshow depends on assumptions its own documentation quietly contradicts.
Explain Like I'm 5 — the whole thing in plain language.
Anthropic makes the Claude AI models. On September 22, 2026, it released a new one called Opus 5.5 and said it's about 40% cheaper to run than the last one, Opus 5.
Part of that is true and easy to check. Anthropic's own price list shows a straight 20% cut on what you pay per chunk of text (called a "token") going in and coming out, plus a bigger 60% cut on a "cache" feature that lets the AI remember things without repaying full price each time. Those numbers are real and unconditional.
The other 20%, the gap between the 20% you can verify and the 40% Anthropic advertised, comes from a guess: that the new model needs less effort to do the same job as the old one. But Anthropic's own technical notes for developers say something that cuts the other way: if you leave your settings exactly the way they were on the old model, the new one actually thinks more, not less, which costs more, not less. The savings only show up if you also accept a separate change, a lower "effort" default, that Anthropic quietly turned on alongside the price cut.
There's also a catch buried in the safety system. Sometimes the cheaper new model has to quietly hand your request to an older, pricier model behind the scenes for safety review, and when that happens, the AI can lose its own notes on what it was doing and has to start that step over, using more words, which means more cost.
Anthropic released this the same week it's preparing to go public at a value near $2 trillion, and about ninety minutes before a rival, OpenAI, cut its own prices by roughly half. Cheaper AI is real this week. "40% cheaper" is Anthropic's own estimate of how you'll use it, not a fixed price.