Configuration Reference

Fresh

File Locations

Path	Purpose
~/.letta/	Global Letta Code data directory
~/.letta/agents/<id>/	Per-agent data and config
~/.letta/agents/<id>/memory/	Git-backed MemFS storage
~/.letta/agents/<id>/skills/	Agent-scoped skills
~/.letta/skills/	Global skills
~/.letta/channels/	Channel configuration
~/.letta/channels/accounts.json	Channel credentials and policies
~/.letta/channels/routing.yaml	Chat-to-agent bindings
~/.letta/channels/pairing.yaml	Pending/approved pairings
.letta/agents/	Project-scoped subagent definitions
.agents/skills/	Project-scoped skills (preferred)
.skills/	Project-scoped skills (legacy)

System Prompt Presets

Preset	Model Target	Description
default	General	Standard coding assistant
letta-claude	Claude	Optimized for Anthropic Claude
letta-codex	OpenAI Codex	Optimized for Codex models
letta-gemini	Google Gemini	Optimized for Gemini models

Minimal model-specific variants are also available for each preset.

Memory Block Configuration

MemFS File Format

---
description: "Brief description of this memory block"
limit: 50000
---

Content of the memory block goes here.

Common Memory Block Labels

Label	Purpose
persona	Agent identity and personality
human	User profile and preferences
project	Current project context
style	Code style preferences

SDK Configuration

Agent Creation Options

interface AgentOptions {
  memoryBlocks?: MemoryBlock[] | 'preset';
  systemPrompt?: string;     // Preset name or custom string
  model?: string;            // Model identifier
  embedding?: string;        // Embedding model
}

Session Runtime Options

interface SessionOptions {
  allowedTools?: string[];       // Tool whitelist
  disallowedTools?: string[];    // Tool blacklist
  permissionMode?: string;       // 'acceptEdits' | 'plan'
  canUseTool?: (tool) => boolean; // Custom callback
  workingDirectory?: string;     // Agent CWD
  reflection?: boolean;          // Enable reflection
  sleeptime?: SleeptimeConfig;   // Reflection config
  memfs?: boolean;               // Toggle MemFS
}

Subagent Frontmatter

---
name: my-subagent          # Required: lowercase, starts with letter
description: What it does  # Required: shown in Task tool
tools: Read, Glob, Grep    # Optional: comma-separated or 'all'
model: sonnet              # Optional: haiku, sonnet, opus
memoryBlocks: human, persona # Optional: 'all', 'none', or list
skills: skill-name          # Optional: auto-load skills
---

Built-in Subagent Models

Subagent	Default Model
explore	auto-fast
fork	inherit
general-purpose	auto
history-analyzer	auto
memory	auto
init	auto-fast
recall	auto-fast
reflection	auto

DM Policies (Channels)

Policy	Description
pairing	One-time codes requiring operator approval
allowlist	Pre-configured user IDs only
open	Anyone can message; routes auto-provision

Environment Variables

Variable	Purpose
LETTA_CONVERSATION_ID	Default conversation for scheduled tasks