Bedrock Agentcore > Structures > HarnessContentBlockStartEvent HarnessContentBlockStartEvent¶ Structure Class¶ HarnessContentBlockStartEvent dataclass ¶ Event indicating the start of a content block. Attributes¶ content_block_index instance-attribute ¶ content_block_index: int The index of the content block within the message. start instance-attribute ¶ start: HarnessContentBlockStart The content block start payload.