event: message_start data: {"type":"message_start","message":{"id":"msg_think01","type":"message","role":"assistant","content":[],"model":"claude-sonnet-4-5-20250929","stop_reason":null,"usage":{"input_tokens":20,"output_tokens":0}}} event: content_block_start data: {"type":"content_block_start","index":0,"content_block":{"type":"thinking","thinking":""}} event: content_block_delta data: {"type":"content_block_delta","index":0,"delta":{"type":"thinking_delta","thinking":"Let me think about this..."}} event: content_block_delta data: {"type":"content_block_delta","index":0,"delta":{"type":"signature_delta","signature":"sig_abc123"}} event: content_block_stop data: {"type":"content_block_stop","index":0} event: content_block_start data: {"type":"content_block_start","index":1,"content_block":{"type":"text","text":""}} event: content_block_delta data: {"type":"content_block_delta","index":1,"delta":{"type":"text_delta","text":"The answer is 42."}} event: content_block_stop data: {"type":"content_block_stop","index":1} event: message_delta data: {"type":"message_delta","delta":{"stop_reason":"end_turn","stop_sequence":null},"usage":{"output_tokens":18}} event: message_stop data: {"type":"message_stop"}