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Acontext preserves Anthropic-specific flags like cache_control for prompt caching and thinking blocks for extended thinking.

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Prompt Cache

client.sessions.store_message(
    session_id=session.id,
    blob={
        "role": "user",
        "content": [
            {
                "type": "text",
                "text": "<the entire contents of Pride and Prejudice>",
                "cache_control": {"type": "ephemeral"}
            }
        ]
    },
    format="anthropic"
)

# Retrieved messages preserve the cache_control flag
messages = client.sessions.get_messages(session_id=session.id, format="anthropic")

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Thinking Blocks

Acontext natively stores thinking blocks from Claude’s extended thinking feature. The signature is preserved for multi-turn conversation continuity. 
client.sessions.store_message(
    session_id=session.id,
    blob={
        "role": "assistant",
        "content": [
            {
                "type": "thinking",
                "thinking": "Let me reason step by step...",
                "signature": "EqoBCkgIAxgCIkD..."
            },
            {
                "type": "text",
                "text": "The answer is 42."
            }
        ]
    },
    format="anthropic"
)

# Retrieved in Anthropic or Gemini format: thinking blocks round-trip as native thinking blocks
# Retrieved in OpenAI format: thinking content is downgraded to plain text
If you’re using the Claude Agent SDK, see ClaudeAgentStorage for automatic thinking block handling.