Work with sessions

How sessions persist agent conversation history, and when to use continue, resume, and fork to return to a prior run.

A session is the conversation history the SDK accumulates while your agent works. It contains your prompt, every tool call the agent made, every tool result, and every response. The SDK writes it to disk automatically so you can return to it later.

Returning to a session means the agent has full context from before: files it already read, analysis it already performed, decisions it already made. You can ask a follow-up question, recover from an interruption, or branch off to try a different approach.

This guide covers how to pick the right approach for your app, the SDK interfaces that track sessions automatically, how to capture session IDs and use resume and fork manually, and what to know about resuming sessions across hosts.

Choose an approach

How much session handling you need depends on your application's shape. Session management comes into play when you send multiple prompts that should share context. Within a single query() call, the agent already takes as many turns as it needs, and permission prompts and AskUserQuestion are handled in-loop (they don't end the call).

Continue, resume, and fork

Continue, resume, and fork are option fields you set on query() (ClaudeAgentOptions in Python, Options in TypeScript).

Continue and resume both pick up an existing session and add to it. The difference is how they find that session:

• Continue finds the most recent session in the current directory. You don't track anything. Works well when your app runs one conversation at a time.
• Resume takes a specific session ID. You track the ID. Required when you have multiple sessions (for example, one per user in a multi-user app) or want to return to one that isn't the most recent.

Fork is different: it creates a new session that starts with a copy of the original's history. The original stays unchanged. Use fork to try a different direction while keeping the option to go back.

Automatic session management

Both SDKs offer an interface that tracks session state for you across calls, so you don't pass IDs around manually. Use these for multi-turn conversations within a single process.

Python: ClaudeSDKClient

ClaudeSDKClient handles session IDs internally. Each call to client.query() automatically continues the same session. Call client.receive_response() to iterate over the messages for the current query. The client must be used as an async context manager.

This example runs two queries against the same client. The first asks the agent to analyze a module; the second asks it to refactor that module. Because both calls go through the same client instance, the second query has full context from the first without any explicit resume or session ID:

import asyncio
from claude_agent_sdk import (
    ClaudeSDKClient,
    ClaudeAgentOptions,
    AssistantMessage,
    ResultMessage,
    TextBlock,
)


def print_response(message):
    """Print only the human-readable parts of a message."""
    if isinstance(message, AssistantMessage):
        for block in message.content:
            if isinstance(block, TextBlock):
                print(block.text)
    elif isinstance(message, ResultMessage):
        cost = (
            f"${message.total_cost_usd:.4f}"
            if message.total_cost_usd is not None
            else "N/A"
        )
        print(f"[done: {message.subtype}, cost: {cost}]")


async def main():
    options = ClaudeAgentOptions(
        allowed_tools=["Read", "Edit", "Glob", "Grep"],
    )

    async with ClaudeSDKClient(options=options) as client:
        # First query: client captures the session ID internally
        await client.query("Analyze the auth module")
        async for message in client.receive_response():
            print_response(message)

        # Second query: automatically continues the same session
        await client.query("Now refactor it to use JWT")
        async for message in client.receive_response():
            print_response(message)


asyncio.run(main())

See the Python SDK reference for details on when to use ClaudeSDKClient vs the standalone query() function.

TypeScript: continue: true

The stable TypeScript SDK (the query() function used throughout these docs, sometimes called V1) doesn't have a session-holding client object like Python's ClaudeSDKClient. Instead, pass continue: true on each subsequent query() call and the SDK picks up the most recent session in the current directory. No ID tracking required.

This example makes two separate query() calls. The first creates a fresh session; the second sets continue: true, which tells the SDK to find and resume the most recent session on disk. The agent has full context from the first call:

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

// First query: creates a new session
for await (const message of query({
  prompt: "Analyze the auth module",
  options: { allowedTools: ["Read", "Glob", "Grep"] }
})) {
  if (message.type === "result" && message.subtype === "success") {
    console.log(message.result);
  }
}

// Second query: continue: true resumes the most recent session
for await (const message of query({
  prompt: "Now refactor it to use JWT",
  options: {
    continue: true,
    allowedTools: ["Read", "Edit", "Write", "Glob", "Grep"]
  }
})) {
  if (message.type === "result" && message.subtype === "success") {
    console.log(message.result);
  }
}

Use session options with query()

Capture the session ID

Resume and fork require a session ID. Read it from the session_id field on the result message (ResultMessage in Python, SDKResultMessage in TypeScript), which is present on every result regardless of success or error. In TypeScript the ID is also available earlier as a direct field on the init SystemMessage; in Python it's nested inside SystemMessage.data.

import asyncio
from claude_agent_sdk import query, ClaudeAgentOptions, ResultMessage


async def main():
session_id = None

async for message in query(
prompt="Analyze the auth module and suggest improvements",
options=ClaudeAgentOptions(
allowed_tools=["Read", "Glob", "Grep"],
),
):
if isinstance(message, ResultMessage):
session_id = message.session_id
if message.subtype == "success":
print(message.result)

print(f"Session ID: {session_id}")
return session_id


session_id = asyncio.run(main())

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

let sessionId: string | undefined;

for await (const message of query({
prompt: "Analyze the auth module and suggest improvements",
options: { allowedTools: ["Read", "Glob", "Grep"] }
})) {
if (message.type === "result") {
sessionId = message.session_id;
if (message.subtype === "success") {
console.log(message.result);
}
}
}

console.log(`Session ID: ${sessionId}`);

Resume by ID

Pass a session ID to resume to return to that specific session. The agent picks up with full context from wherever the session left off. Common reasons to resume:

• Follow up on a completed task. The agent already analyzed something; now you want it to act on that analysis without re-reading files.
• Recover from a limit. The first run ended with error_max_turns or error_max_budget_usd (see Handle the result); resume with a higher limit.
• Restart your process. You captured the ID before shutdown and want to restore the conversation.

This example resumes the session from Capture the session ID with a follow-up prompt. Because you're resuming, the agent already has the prior analysis in context:

# Earlier session analyzed the code; now build on that analysis
async for message in query(
prompt="Now implement the refactoring you suggested",
options=ClaudeAgentOptions(
resume=session_id,
allowed_tools=["Read", "Edit", "Write", "Glob", "Grep"],
),
):
if isinstance(message, ResultMessage) and message.subtype == "success":
print(message.result)

// Earlier session analyzed the code; now build on that analysis
for await (const message of query({
prompt: "Now implement the refactoring you suggested",
options: {
resume: sessionId,
allowedTools: ["Read", "Edit", "Write", "Glob", "Grep"]
}
})) {
if (message.type === "result" && message.subtype === "success") {
console.log(message.result);
}
}

To resume sessions across machines or in serverless environments, mirror transcripts to shared storage with a SessionStore adapter.

Fork to explore alternatives

Forking creates a new session that starts with a copy of the original's history but diverges from that point. The fork gets its own session ID; the original's ID and history stay unchanged. You end up with two independent sessions you can resume separately.

This example builds on Capture the session ID: you've already analyzed an auth module in session_id and want to explore OAuth2 without losing the JWT-focused thread. The first block forks the session and captures the fork's ID (forked_id); the second block resumes the original session_id to continue down the JWT path. You now have two session IDs pointing at two separate histories:

# Fork: branch from session_id into a new session
forked_id = None
async for message in query(
prompt="Instead of JWT, implement OAuth2 for the auth module",
options=ClaudeAgentOptions(
resume=session_id,
fork_session=True,
),
):
if isinstance(message, ResultMessage):
forked_id = message.session_id  # The fork's ID, distinct from session_id
if message.subtype == "success":
print(message.result)

print(f"Forked session: {forked_id}")

# Original session is untouched; resuming it continues the JWT thread
async for message in query(
prompt="Continue with the JWT approach",
options=ClaudeAgentOptions(resume=session_id),
):
if isinstance(message, ResultMessage) and message.subtype == "success":
print(message.result)

// Fork: branch from sessionId into a new session
let forkedId: string | undefined;

for await (const message of query({
prompt: "Instead of JWT, implement OAuth2 for the auth module",
options: {
resume: sessionId,
forkSession: true
}
})) {
if (message.type === "system" && message.subtype === "init") {
forkedId = message.session_id; // The fork's ID, distinct from sessionId
}
if (message.type === "result" && message.subtype === "success") {
console.log(message.result);
}
}

console.log(`Forked session: ${forkedId}`);

// Original session is untouched; resuming it continues the JWT thread
for await (const message of query({
prompt: "Continue with the JWT approach",
options: { resume: sessionId }
})) {
if (message.type === "result" && message.subtype === "success") {
console.log(message.result);
}
}

Resume across hosts

Session files are local to the machine that created them. To resume a session on a different host (CI workers, ephemeral containers, serverless), you have two options:

• Move the session file. Persist ~/.claude/projects/<encoded-cwd>/<session-id>.jsonl from the first run and restore it to the same path on the new host before calling resume. The cwd must match.
• Don't rely on session resume. Capture the results you need (analysis output, decisions, file diffs) as application state and pass them into a fresh session's prompt. This is often more robust than shipping transcript files around.

Both SDKs expose functions for enumerating sessions on disk and reading their messages: listSessions() and getSessionMessages() in TypeScript, list_sessions() and get_session_messages() in Python. Use them to build custom session pickers, cleanup logic, or transcript viewers.

Both SDKs also expose functions for looking up and mutating individual sessions: get_session_info(), rename_session(), and tag_session() in Python, and getSessionInfo(), renameSession(), and tagSession() in TypeScript. Use them to organize sessions by tag or give them human-readable titles.

Related resources

• How the agent loop works: Understand turns, messages, and context accumulation within a session
• File checkpointing: Track and revert file changes across sessions
• Python ClaudeAgentOptions: Full session option reference for Python
• TypeScript Options: Full session option reference for TypeScript