An architect needs Claude to reason through a complex multi-step financial analysis, then call a get_market_data tool with specific parameters derived from that reasoning, incorporate the tool result, and reason further before producing a final report. The team is evaluating extended thinking for this use case. What is the correct design for extended thinking with interleaved tool use?

The correct design is enabling extended thinking in the API request with a thinking budget, because Claude can emit a thinking block, then a tool_use block, and after receiving the tool_result continue with additional thinking before the final response; this interleaving is supported and is the intended pattern for complex agentic reasoning tasks. The option that enables extended thinking with budget_tokens: 10000 and places all tool definitions in the system prompt is wrong because tool definitions are not placed in the system prompt — they are passed via the tools parameter in the API request, and the automatic interleaving without configuration claim is misleading. The streaming API option that says tool calls can only occur after all thinking is complete is wrong because it incorrectly states that tool calls can only occur after thinking is complete; interleaving is supported, not prohibited, so requiring the architecture to buffer the full thinking output before processing tool results is unnecessary. The option that treats extended thinking and tool use as mutually exclusive and chains two separate API calls — one with extended thinking for analysis and one with tool definitions for execution — is wrong because extended thinking and tool use are not mutually exclusive; this is a common misconception, and chaining two separate calls would break the continuity of the reasoning chain.