Anthropic's balanced frontier model — top coding and reasoning at mid-tier price.
Claude Sonnet 4 sits between the cheap Flash-class models and the max-depth Opus 4. It delivers frontier-level coding and reasoning at a price teams can run all day, making it the default for serious engineering agents.
Who it's for: Engineering teams and power users who want frontier quality for coding and analysis without Opus-level cost.
Ships large, multi-file features with strong test awareness.
Allocates extra compute to hard problems for better answers.
Clean function calling for autonomous workflows.
Persists context across long sessions and tasks.
Claude Sonnet 4 is the model we'd build an agent on in 2026. Pair it with Opus 4 for the hardest tasks and Flash-class models for high-volume simple work.