Letta
Free tierAn AI research lab building self-improving agents that remember everything and learn continuously.
Key strengths
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Letta — Technical Overview
Letta is an open-source (Apache 2.0) framework for building stateful AI agents with persistent memory and continual self-improvement capabilities. Founded in 2023 and headquartered in San Francisco, Letta is designed for developers who need agents that retain context across sessions, reason in the background, and evolve over time.
Key technical characteristics:
- Persistent memory architecture — agents maintain state across interactions, with git-based memory versioning for auditability and rollback
- Sleep-time compute — agents can perform background reasoning between user interactions, enabling proactive updates and pre-computation
- Self-hostable — deploy on your own infrastructure; the full stack is available via the open-source repo (25,000+ GitHub stars)
- REST API — a first-class API layer enables programmatic agent creation, memory inspection, and lifecycle management
- Protocol integrations — supports MCP (Model Context Protocol) and ACP (Agent Communication Protocol) alongside LLM backends including Claude and ChatGPT
- Multi-channel connectors — Slack, Telegram, Discord, WhatsApp, Signal, GitHub, and Cursor out of the box
- BYOK support — bring your own API keys on the Free plan
Pricing tiers: Free ($0/mo, 3–5 agents, 5 MiB storage, BYOK) · Pro ($20/mo, up to 20 agents, 50 MiB storage) · API Plan ($20/mo, unlimited agents, usage-based) · Teams Pro ($20/seat/mo) · Enterprise (custom).