---
title: Letta Agent SDK reference | Letta Docs
description: Client methods, session interface, and option types for the Letta Agent SDK
---

Use this reference after the [Quickstart](/letta-agent-sdk/quickstart/index.md) when you need method names, session shape, or option interfaces.

### Client methods

| Method                                     | Description                                                                                         |
| ------------------------------------------ | --------------------------------------------------------------------------------------------------- |
| `client.createAgent(options?)`             | Create a new persistent agent                                                                       |
| `client.createSession(agentId?, options?)` | Start a new conversation (uses default agent if no ID provided)                                     |
| `client.resumeSession(id, options?)`       | Resume session (pass `agent-xxx` for default conversation, or `conv-xxx` for specific conversation) |
| `client.prompt(message, agentId?)`         | One-shot query (uses default agent if no ID provided)                                               |

### Session interface

```
interface Session {
  send(message: string): Promise<void>;
  stream(): AsyncGenerator<SDKMessage>;
  close(): void;


  listMessages(options?: ListMessagesOptions): Promise<ListMessagesResult>;


  readonly agentId: string | null;
  readonly conversationId: string | null;
  readonly sessionId: string | null;
}
```

### CreateAgentOptions

Options for `client.createAgent()` - these configure the persistent agent:

```
interface CreateAgentOptions {
  model?: string;
  reasoningEffort?: ReasoningEffort;
  embedding?: string;


  // Memory configuration (choose one approach)
  memory?: Array<string | { label: string; value: string }>;


  // Convenience shortcuts for common presets
  persona?: string;
  human?: string;


  // System prompt (custom string or preset)
  systemPrompt?:
    | string
    | SystemPromptPreset
    | { type: "preset"; preset: SystemPromptPreset; append?: string };


  // Runtime/harness controls available at creation
  skillSources?: SkillSource[];
  systemInfoReminder?: boolean;
  dreaming?: DreamingOptions;
}
```

### CreateSessionOptions

Options for `client.createSession()` and `client.resumeSession()` - these configure runtime behavior:

```
interface CreateSessionOptions {
  // Model configuration
  model?: string;
  reasoningEffort?: ReasoningEffort;


  // System prompt preset (updates the agent)
  systemPrompt?: SystemPromptPreset;


  // Tool restrictions
  allowedTools?: string[];
  disallowedTools?: string[];
  permissionMode?: "default" | "acceptEdits" | "plan" | "bypassPermissions";
  canUseTool?: (
    toolName: string,
    toolInput: object,
  ) => Promise<CanUseToolResponse>;


  // File system
  cwd?: string;


  // Runtime/harness controls
  skillSources?: SkillSource[]; // [] => --no-skills
  systemInfoReminder?: boolean; // false => --no-system-info-reminder
  dreaming?: DreamingOptions;
}
```

Supporting types:

```
type SkillSource = "bundled" | "global" | "agent" | "project";


interface DreamingOptions {
  trigger?: "off" | "step-count" | "compaction-event";
  behavior?: "reminder" | "auto-launch";
  stepCount?: number;
}
```