import { createSession } from '@letta-ai/letta-code-sdk';

const session = createSession();
await session.send('Find and fix the bug in auth.py');
for await (const msg of session.stream()) {
  if (msg.type === 'assistant') console.log(msg.content);
}

Installation

npm install @letta-ai/letta-code-sdk

Quick Start

One-shot prompt

import { prompt } from '@letta-ai/letta-code-sdk';

// One-shot (uses default agent - like `letta -p`)
const result = await prompt('What is 2 + 2?');
console.log(result.result);

// One-shot with specific agent
const result2 = await prompt('Run: echo hello', agentId);

Multi-turn session

import { createAgent, resumeSession } from '@letta-ai/letta-code-sdk';

// Create an agent with custom memory (has default conversation)
const agentId = await createAgent({
  memory: ['persona'],
  persona: 'You are a helpful coding assistant for TypeScript projects'
});

// Resume the default conversation
await using session = resumeSession(agentId);

await session.send('What is 5 + 3?');
for await (const msg of session.stream()) {
  if (msg.type === 'assistant') console.log(msg.content);
}

await session.send('Multiply that by 2');
for await (const msg of session.stream()) {
  if (msg.type === 'assistant') console.log(msg.content);
}

Persistent memory

Agents persist across sessions and remember context:

import { createAgent, resumeSession } from '@letta-ai/letta-code-sdk';

// Create agent and teach it something
const agentId = await createAgent();
const session1 = resumeSession(agentId);
await session1.send('Remember: the secret word is "banana"');
for await (const msg of session1.stream()) { /* ... */ }
session1.close();

// Later... resume the default conversation
await using session2 = resumeSession(agentId);
await session2.send('What is the secret word?');
for await (const msg of session2.stream()) {
  if (msg.type === 'assistant') console.log(msg.content); // "banana"
}

Multi-threaded Conversations

Run multiple concurrent conversations with the same agent. Each conversation has its own message history while sharing the agent's persistent memory.

import { createAgent, createSession, resumeSession } from '@letta-ai/letta-code-sdk';

// Create an agent (has default conversation)
const agentId = await createAgent();

// Resume the default conversation
const session1 = resumeSession(agentId);
await session1.send('Hello!');
for await (const msg of session1.stream()) { /* ... */ }
const conversationId = session1.conversationId; // Save this!
session1.close();

// Resume a specific conversation by ID
await using session2 = resumeSession(conversationId);  // auto-detects conv-xxx
await session2.send('Continue our discussion...');
for await (const msg of session2.stream()) { /* ... */ }

// Create a NEW conversation on the same agent
await using session3 = createSession(agentId);
await session3.send('Start a fresh thread...');
// session3.conversationId is different from conversationId

// Start fresh conversation with default agent
await using session4 = createSession();

Key concepts:

Agent (agentId): Persistent entity with memory that survives across sessions
Conversation (conversationId): A message thread within an agent
Session: A single execution/connection
Default conversation: Always exists after createAgent() - use resumeSession(agentId) to access it

Agents remember across conversations (via memory blocks), but each conversation has its own message history.

Session Configuration

System Prompt

Choose from built-in presets or provide a custom prompt:

// Use a preset
createSession(agentId, {
  systemPrompt: { type: 'preset', preset: 'letta-claude' }
});

// Use a preset with additional instructions
createSession(agentId, {
  systemPrompt: { 
    type: 'preset', 
    preset: 'letta-claude',
    append: 'Always respond in Spanish.'
  }
});

// Use a completely custom prompt
createSession(agentId, {
  systemPrompt: 'You are a helpful Python expert.'
});

Available presets:

default / letta-claude - Full Letta Code prompt (Claude-optimized)
letta-codex - Full Letta Code prompt (Codex-optimized)
letta-gemini - Full Letta Code prompt (Gemini-optimized)
claude - Basic Claude (no skills/memory instructions)
codex - Basic Codex
gemini - Basic Gemini

API Reference

Functions

Function	Description
`createAgent(options?)`	Create new agent with custom memory/prompt. No options = blank agent with default memory blocks. Returns `agentId`
`createSession(agentId?, options?)`	New conversation on specified agent. No agentId = uses LRU agent (or creates "Memo" if none exists)
`resumeSession(id, options?)`	Resume session - pass `agent-xxx` for default conv, `conv-xxx` for specific conv
`prompt(message, agentId?)`	One-shot query with default/specified agent (like `letta -p`)

Session

Property/Method	Description
`send(message)`	Send user message
`stream()`	AsyncGenerator yielding messages
`close()`	Close the session
`agentId`	Agent ID (for resuming later)
`sessionId`	Current session ID
`conversationId`	Conversation ID (for resuming specific thread)

Options

CreateAgentOptions (for createAgent() - full control):

// Create blank agent
await createAgent();

// Create agent with custom memory and system prompt
await createAgent({
  model: 'claude-sonnet-4',
  systemPrompt: 'You are a helpful Python expert.',
  memory: [
    { label: 'persona', value: 'You are a senior Python developer' },
    { label: 'project', value: 'FastAPI backend for a todo app' }
  ]
});

CreateSessionOptions (for createSession() / resumeSession() - runtime options):

// Start session with permissions
createSession(agentId, {
  permissionMode: 'bypassPermissions',
  allowedTools: ['Bash', 'Glob'],
  cwd: '/path/to/project'
});

Available system prompt presets:

default / letta-claude, letta-codex, letta-gemini - Full Letta Code prompts
claude, codex, gemini - Basic (no skills/memory instructions)

Message Types

// Streamed during receive()
interface SDKAssistantMessage {
  type: 'assistant';
  content: string;
  uuid: string;
}

// Final message
interface SDKResultMessage {
  type: 'result';
  success: boolean;
  result?: string;
  error?: string;
  durationMs: number;
  conversationId: string;
}

Examples

See examples/ for comprehensive examples including:

Basic session usage
Multi-turn conversations
Session resume with persistent memory
Multi-threaded conversations (createSession, resumeSession)
System prompt configuration
Memory block customization
Tool execution (Bash, Glob, Read, etc.)

Run examples:

bun examples/v2-examples.ts all

# Run just conversation tests
bun examples/v2-examples.ts conversations

Internals

CLI Mapping

The SDK spawns the Letta Code CLI as a subprocess. Here's how API calls map to CLI flags:

Function	CLI Flags	Behavior
`createSession()`	`--new`	LRU agent + new conversation
`createSession(agentId)`	`--agent X --new`	Specified agent + new conversation
`createAgent()`	`--new-agent`	New agent + default conversation
`resumeSession(agentId)`	`--agent X --default`	Specified agent + default conversation
`resumeSession(convId)`	`--conversation X`	Derived agent + specified conversation
`prompt(msg)`	(none)	LRU agent + default conversation
`prompt(msg, agentId)`	`--agent X --new`	Specified agent + new conversation

Key concepts:

LRU agent: Most recently used agent from .letta/settings.local.json, or creates "Memo" if none exists
Default conversation: The agent's primary message history (always exists)
New conversation: Fresh message thread, isolated from other conversations

License

Apache-2.0