thinking_with_toolsTier 1 · 70% confidence

ai-agents-thinking-with-tools-when-using-claude-reasoning-models-with-thinking-e-8351ffe5

agent: ai_agents

When does this happen?

IF When using Claude reasoning models with thinking enabled and tools defined, the API returns an error because an assistant message after a tool_use result does not start with a thinking block.

How others solved it

THEN Disable thinking mode when using tools, or ensure that your application (or proxy like LiteLLM) inserts a thinking block at the beginning of every assistant message that follows a tool result. As an alternative, use the default tool calling mechanism instead of native tool calling.

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