Sessions ↗

anthropic-platform guide intermediate agents

Original Documentation

Understanding how the Claude Agent SDK handles sessions and session resumption

Session Management#

The Claude Agent SDK provides session management capabilities for handling conversation state and resumption. Sessions allow you to continue conversations across multiple interactions while maintaining full context.

How Sessions Work#

When you start a new query, the SDK automatically creates a session and returns a session ID in the initial system message. You can capture this ID to resume the session later.

Getting the Session ID#


let sessionId: string | undefined;

const response = query({
  prompt: "Help me build a web application",
  options: {
    model: "claude-opus-4-6"
  }
});

for await (const message of response) {
  // The first message is a system init message with the session ID
  if (message.type === "system" && message.subtype === "init") {
    sessionId = message.session_id;
    console.log(`Session started with ID: ${sessionId}`);
    // You can save this ID for later resumption
  }

  // Process other messages...
  console.log(message);
}

// Later, you can use the saved sessionId to resume
if (sessionId) {
  const resumedResponse = query({
    prompt: "Continue where we left off",
    options: {
      resume: sessionId
    }
  });
}

from claude_agent_sdk import query, ClaudeAgentOptions

session_id = None

async for message in query(
    prompt="Help me build a web application",
    options=ClaudeAgentOptions(model="claude-opus-4-6"),
):
    # The first message is a system init message with the session ID
    if hasattr(message, "subtype") and message.subtype == "init":
        session_id = message.data.get("session_id")
        print(f"Session started with ID: {session_id}")
        # You can save this ID for later resumption

    # Process other messages...
    print(message)

# Later, you can use the saved session_id to resume
if session_id:
    async for message in query(
        prompt="Continue where we left off",
        options=ClaudeAgentOptions(resume=session_id),
    ):
        print(message)

Resuming Sessions#

The SDK supports resuming sessions from previous conversation states, enabling continuous development workflows. Use the resume option with a session ID to continue a previous conversation.


// Resume a previous session using its ID
const response = query({
  prompt: "Continue implementing the authentication system from where we left off",
  options: {
    resume: "session-xyz", // Session ID from previous conversation
    model: "claude-opus-4-6",
    allowedTools: ["Read", "Edit", "Write", "Glob", "Grep", "Bash"]
  }
});

// The conversation continues with full context from the previous session
for await (const message of response) {
  console.log(message);
}

from claude_agent_sdk import query, ClaudeAgentOptions

# Resume a previous session using its ID
async for message in query(
    prompt="Continue implementing the authentication system from where we left off",
    options=ClaudeAgentOptions(
        resume="session-xyz",  # Session ID from previous conversation
        model="claude-opus-4-6",
        allowed_tools=["Read", "Edit", "Write", "Glob", "Grep", "Bash"],
    ),
):
    print(message)

# The conversation continues with full context from the previous session

The SDK automatically handles loading the conversation history and context when you resume a session, allowing Claude to continue exactly where it left off.

To track and revert file changes across sessions, see File Checkpointing.

Forking Sessions#

When resuming a session, you can choose to either continue the original session or fork it into a new branch. By default, resuming continues the original session. Use the forkSession option (TypeScript) or fork_session option (Python) to create a new session ID that starts from the resumed state.

When to Fork a Session#

Forking is useful when you want to:

Explore different approaches from the same starting point
Create multiple conversation branches without modifying the original
Test changes without affecting the original session history
Maintain separate conversation paths for different experiments

Forking vs Continuing#

Behavior	`forkSession: false` (default)	`forkSession: true`
Session ID	Same as original	New session ID generated
History	Appends to original session	Creates new branch from resume point
Original Session	Modified	Preserved unchanged
Use Case	Continue linear conversation	Branch to explore alternatives

Example: Forking a Session#


// First, capture the session ID
let sessionId: string | undefined;

const response = query({
  prompt: "Help me design a REST API",
  options: { model: "claude-opus-4-6" }
});

for await (const message of response) {
  if (message.type === "system" && message.subtype === "init") {
    sessionId = message.session_id;
    console.log(`Original session: ${sessionId}`);
  }
}

// Fork the session to try a different approach
const forkedResponse = query({
  prompt: "Now let's redesign this as a GraphQL API instead",
  options: {
    resume: sessionId,
    forkSession: true, // Creates a new session ID
    model: "claude-opus-4-6"
  }
});

for await (const message of forkedResponse) {
  if (message.type === "system" && message.subtype === "init") {
    console.log(`Forked session: ${message.session_id}`);
    // This will be a different session ID
  }
}

// The original session remains unchanged and can still be resumed
const originalContinued = query({
  prompt: "Add authentication to the REST API",
  options: {
    resume: sessionId,
    forkSession: false, // Continue original session (default)
    model: "claude-opus-4-6"
  }
});

from claude_agent_sdk import query, ClaudeAgentOptions

# First, capture the session ID
session_id = None

async for message in query(
    prompt="Help me design a REST API",
    options=ClaudeAgentOptions(model="claude-opus-4-6"),
):
    if hasattr(message, "subtype") and message.subtype == "init":
        session_id = message.data.get("session_id")
        print(f"Original session: {session_id}")

# Fork the session to try a different approach
async for message in query(
    prompt="Now let's redesign this as a GraphQL API instead",
    options=ClaudeAgentOptions(
        resume=session_id,
        fork_session=True,  # Creates a new session ID
        model="claude-opus-4-6",
    ),
):
    if hasattr(message, "subtype") and message.subtype == "init":
        forked_id = message.data.get("session_id")
        print(f"Forked session: {forked_id}")
        # This will be a different session ID

# The original session remains unchanged and can still be resumed
async for message in query(
    prompt="Add authentication to the REST API",
    options=ClaudeAgentOptions(
        resume=session_id,
        fork_session=False,  # Continue original session (default)
        model="claude-opus-4-6",
    ),
):
    print(message)

Link last verified June 7, 2026. View original ↗

Source: Anthropic Platform Docs

Link last verified: 2026-02-26