Claude Sonnet excels when reasoning is the bottleneck. Extended thinking mode trades tokens for chain-of-thought explainability, and the larger context window makes it the default for document-heavy workflows, agent state machines, or long-running conversations. Teams building agents that reason through complex multi-step problems, or that process long documents and need to stay within a token budget, pick Sonnet.
GPT-4o wins for multimodal agility and closed-loop workflows. The vision-to-text-to-action loop is tighter, video input matters for certain use cases (video summaries, visual QA), and the ecosystem lock-in with ChatGPT, Canvas, and GPT Store integration can be a feature rather than a constraint. Teams with canvas-native workflows or that need tight OpenAI integrations pick GPT-4o.
Most production teams run both. Use Sonnet for reasoning-heavy inference, long contexts, and agent state. Use GPT-4o for multimodal tasks and ChatGPT integration. The pricing delta is narrow enough that the architecture wins pay for themselves in 2-3 days of compute. Pick one only if budget forces a choice; otherwise, the agents pick their own model based on the job shape.