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Claude Opus 4.5
Long-context reasoning model. The default for agents that plan multi-step work and read large documents end to end.
Opus is the model to reach for when the work does not fit in one prompt: a contract read clause by clause, a flow that has to decide which of six branches to take, a research question that needs four tool calls before it can be answered.
It is the most expensive model in the catalogue, and in Ragenta that is a number you can see rather than guess — every run records the credits it spent, broken down by step. Most workspaces put Opus on the planning step and a cheaper model on the rest.