Content Block Types

Messages carry content in blocks, each typed by type field:

text: Plain text content from Claude.
thinking: Extended thinking (reasoning) block when includeThinking: true. Only visible if model supports thinking.
tool_use: Tool invocation: id, name, input (object).
tool_result: Result from a tool call: tool_use_id (links to prior tool_use), content (text or structured), is_error (boolean).
image: Image block with source (type: 'base64' | 'url'), media type, and dimensions.
document: PDF or document attachment.
redaction: Redacted content (internal use; rarely surfaced to SDK consumers).