How does Claude Sonnet 5's tool-use behavior differ from Claude Sonnet 4.6's?

Anthropic frames Sonnet 5 as its most agentic Sonnet model yet, specifically calling out improved planning, tool use - including browsers and terminals - and the ability to run autonomously at a level that previously required larger, more expensive models.

This reflects a substantive capability shift rather than just an API-level change: the same categories of tools that Sonnet 4.6 could call are still supported, but Sonnet 5 is reported to plan and execute multi-step tool-use sequences more reliably, finishing tasks that earlier Sonnet versions would sometimes stall on partway through.

Because the underlying tool definitions and response shapes are documented as unchanged from Sonnet 4.6, this improvement shows up as better decision-making about when and how to use tools within an existing integration, not as a change to how tools themselves need to be defined or wired up.

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