Claude Opus 4.5 is the more capable and more expensive model in the 4.5 lineup, while Sonnet 4.5 is typically the recommended default for everyday coding tasks. Anthropic positions Sonnet 4.5 as the balanced choice for speed and cost, and Opus 4.5 as the option for maximum reasoning ability. For many development tasks—writing functions, generating unit tests, or making small refactors—Sonnet 4.5 usually performs well enough and responds faster.
Where Opus 4.5 stands out is in larger, more complex reasoning workloads. These include understanding large repositories, coordinating multi-step changes, debugging intricate behavior, or planning architectural migrations. On software-engineering benchmark tasks, Claude Opus 4.5 achieves higher scores, which reflects its ability to maintain longer chains of reasoning and manage difficult code navigation. Developers who frequently need deep analyses or multi-file refactors benefit most from Opus 4.5’s extended reasoning capabilities.
Cost considerations also matter when choosing between the two. Claude Opus 4.5 is priced at $5 per million input tokens and $25 per million output tokens, which means it should usually be reserved for tasks where its additional capabilities provide clear value. In a retrieval-augmented setup—such as using Milvus or Zilliz Cloud to store code embeddings—you can run most interactions on Sonnet 4.5, and call Opus 4.5 only when the agent or developer tool encounters a particularly complex issue. This hybrid approach keeps costs predictable while still providing access to Opus 4.5’s strongest features.