Guides

Session Management

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

import { query } from "@anthropic-ai/claude-agent-sdk"

let sessionId: string | undefined

const response = query({
  prompt: "Help me build a web application",
  options: {
    model: "claude-sonnet-4-5"
  }
})

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
    }
  })
}

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.

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

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

import { query } from "@anthropic-ai/claude-agent-sdk"

let sessionId: string | undefined

const response = query({
  prompt: "Help me build a web application",
  options: {
    model: "claude-sonnet-4-5"
  }
})

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
    }
  })
}

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.

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 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