Response.Message is a pointer to content.AIMessage. The pointer is nil when a serving path has no assistant representation; when present, its Blocks slice is the authoritative ordered output.

Read variants

func render(message *content.AIMessage) {
	if message == nil {
		return
	}
	for _, block := range message.Blocks {
		switch typed := block.(type) {
		case *content.TextBlock:
			fmt.Print(typed.Text)
		case *content.ThinkingBlock:
			// Apply the product's reasoning-visibility policy.
		case *content.ToolUseBlock:
			// Validate typed.Input before executing typed.Name.
		}
	}
}

Thinking and tool-use blocks are not folded into text automatically. Preserve the block order, and use Usage on the AI message only when the message-level result carries it. The top-level Response.Usage is the response-level normalized metadata.

Tool-call continuation

When a ToolUseBlock appears, correlate its ID and append a ToolResultMessage to the next request. A response with FinishReasonToolUse is not a final natural-language answer by itself.

Proof

Source: inference/client.go, core/content/message.go
Tests: core/content/message_json_test.go, inference/structured_result_test.go

Related: AIMessage, Tool-call deltas.