🤖 Single Agent: One co agent per user, automatically created on first login
🧠 Persistent Memory: Advanced memory blocks that evolve over time
💬 Smooth Streaming: Token-buffered streaming (50 FPS) for consistent text appearance
🎨 Polished UI: Clean, minimal interface with animated message transitions
🌓 Theme Toggle: Switch between light and dark modes
🔧 Tool Support: Web search, archival memory, conversation search
📱 Cross-platform: iOS, Android, and Web support via React Native + Expo
🔒 Secure: API token storage with AsyncStorage/SecureStore

Architecture#

co uses a simplified single-agent architecture:

Login: User enters Letta API key
Agent Discovery: App searches for agent with co-app tag
Auto-creation: If no co agent exists, creates one automatically
Chat: User chats directly with their co agent

co Agent Configuration#

co is created with:

Model: anthropic/claude-sonnet-4-5-20250929
Tools: send_message, archival_memory_insert, archival_memory_search, conversation_search, web_search, fetch_webpage
Memory Blocks:
- persona: co's adaptive personality
- human: User profile that evolves
- approach: Conversation and memory approach
- working_theories: Active theories about the user
- notes_to_self: Reminders for future reference
- active_questions: Questions to explore
- conversation_summary: Ongoing conversation overview

Getting Started#

Prerequisites#

Node.js 18+
npm or yarn
Expo CLI
Letta API token from letta.com

Installation#

# Install dependencies
npm install

# Start development server
npm start

# For production performance (recommended)
npm run web:prod

Run Options#

Web: npm run web or press w
iOS: Press i (requires Xcode)
Android: Press a (requires Android Studio)
Mobile Device: Use Expo Go app and scan QR code

First Use#

Launch the app
Enter your Letta API key
Wait for co to initialize (creates agent if needed)
Start chatting!

Project Structure#

co/
├── App.tsx                   # Main application
├── CoLoginScreen.tsx         # Login/authentication
├── web-styles.css            # Web-specific CSS for focus states and themes
├── src/
│   ├── api/
│   │   └── lettaApi.ts       # Letta API client
│   ├── components/
│   │   ├── MessageContent.tsx           # Markdown message rendering
│   │   ├── ExpandableMessageContent.tsx # Collapsible long messages
│   │   ├── ToolCallItem.tsx             # Tool execution display
│   │   └── LogoLoader.tsx               # Loading animations
│   ├── types/
│   │   └── letta.ts          # TypeScript definitions
│   ├── utils/
│   │   ├── coAgent.ts        # co agent creation logic
│   │   └── storage.ts        # AsyncStorage wrapper
│   └── theme/
│       ├── index.ts          # Theme system
│       ├── colors.ts         # Color palette
│       └── typography.ts     # Font definitions

Key Features#

Smooth Token Streaming#

Messages stream at 50 FPS with a token buffer that releases 1-3 characters at a time for consistent, natural text appearance. A hollow circle indicator (○) appears at the end of streaming text.

Animated Message Layout#

When you send a message:

Message appears at the bottom
An animated spacer grows beneath it (400ms animation)
Your message smoothly rises to the top of the viewport
co's response fills the reserved space below

This creates a clean reading experience where your message stays visible with room for the response.

Theme Support#

Toggle between light and dark modes with inverted text input styling:

Dark mode: White background input with black text
Light mode: Black background input with white text

Memory Viewer#

Access co's memory blocks through the sidebar to see what co has learned about you and how it's evolving its understanding over time.

Customizing co#

Modify Personality#

Edit src/utils/coAgent.ts and update:

System prompt
Memory block initial values
Available tools
Model selection

Add Memory Blocks#

Add new blocks to the memoryBlocks array in createCoAgent():

{
  label: 'custom_block',
  value: 'Custom content here...',
}

Change Model#

Update the model field in findOrCreateCo():

model: 'openai/gpt-4.1',  // or other supported models

Development#

Tech Stack#

React Native + Expo: Cross-platform framework
TypeScript: Type safety
Letta SDK (@letta-ai/letta-client): AI agent framework
AsyncStorage/SecureStore: Persistent storage
React Native Markdown Display: Markdown rendering
Lexend Font: Custom typography

Available Scripts#

npm start - Start Expo dev server
npm run web - Run in browser (dev mode)
npm run android - Run on Android
npm run ios - Run on iOS
npx expo start -c - Clear cache and restart

Production Build#

For better performance:

# Development with production optimizations
npx expo start --web --no-dev --minify

# Static production build
npx expo export:web
npx serve web-build

API Integration#

co connects to Letta's API:

GET /agents?tags=co-app - Find co agent
POST /agents - Create co agent
GET /agents/{id}/messages - Load message history
POST /agents/{id}/messages/streaming - Stream messages
GET /agents/{id}/blocks - View memory blocks

Troubleshooting#

Agent Not Found#

If co fails to initialize:

Check API token validity at letta.com
Verify network connection
Check console logs for errors
Try logging out and back in

Memory Blocks Not Loading#

Ensure agent is fully initialized
Check that listAgentBlocks() has proper permissions
Verify agent ID is correct

Streaming Issues#

Check network stability
Verify streaming endpoint support
Review console logs for chunk errors
Try clearing Expo cache: npx expo start -c

Slow Performance#

Run the app with production optimizations:

npx expo start --web --no-dev --minify

License#

MIT License

Clone this repository

co#

Features#