Open Claude on a Pro, Max, Ultra or Team plan and the model already selected is now Opus 5.5. Anthropic changed the default, so people who chat on Sonnet by habit and only reach for Opus on big jobs will land on the larger model unless they pick another.
Anthropic paired the change with a warning that prompts written for older models can hold this one back. The first habit to drop is typing “think hard” or “think carefully”.
Anthropic’s model guide says Opus 5.5 always thinks and sizes the effort itself from the request and the effort setting. Anthropic tested prompts with those phrases stripped out: answers began sooner and quality did not visibly fall. Medium is where it ships, and in the company’s own coding and knowledge-work tests that setting equalled or beat Opus 5 running at High. Moving to High makes sense only when Medium falls short. You change it by tapping the model name beside the send button.
Why make the pricier model the default? Anthropic argues that a stronger model often needs fewer steps, which claws back much of the extra cost per token. Its example: for an invented merger between two HR software firms, Opus 5.5 produced an Excel model and a presentation in 63 minutes at half the cost, where Opus 5 needed 93.
The rest of the line-up keeps its jobs. Haiku 5.5 is the quick, cheap option for lookups and sorting data, and the first Haiku with effort controls. Sonnet 5.5 fits tasks with a clear brief, but pushed to Extra high or Max its cost per task approaches Opus 5.5, so Anthropic says to switch at that point. Fable 5.2 is the heavyweight for long reasoning and agent runs. It can be used on any paid plan, with a catch: on Pro it draws on usage credits.
On strengths, the company points to spreadsheets, reports, financial work and charts. One research test hid the earnings release inside a saved copy of the web and failed any report with a single made-up figure or quote; 16 of 18 reports passed. Reading charts is another claimed gain: even on its lowest setting the model beat the older Opus at its top setting. All of these tests were run by Anthropic itself.
Other tips in the guide: describe the finished result in your first message, attach a chart rather than retyping its numbers, name the specific design styles you dislike, and paste in your house style if you want writing to match. One cost to know about: models with higher prices burn through plan limits faster, so defaulting to Opus can bring the cap closer.
