Letta

What it is for

Letta is an open-source harness for stateful agents: memory that persists, skills the agent loads when relevant, and a web app or CLI that keeps learning. Use it when the job is an agent that remembers you across sessions, not when you want a one-shot chat.

What makes it unique: the cover is the official letta-ai/letta GitHub file list — AGENTS.md, Apache-2.0, README — not a marketing poster. The current harness also lives in letta-ai/letta-code.

Key features

• Persistent memory — /init bootstraps memory; /memory and /doctor inspect and refine blocks; the agent writes lessons from your feedback (Quickstart; Memory). Remembering, not another prompt.
• Skills — reusable instruction packs (Agent Skills standard; Hermes / ClawHub installs) the agent loads when the job matches (Skills; Quickstart). A playbook, not a chat turn.
• Mods — trusted code that changes the runtime (tools, commands, UI, context). Catalog examples: image-understanding, memfs-search, plan-mode (Quickstart). Harness plugins, not a second agent.
• Schedules — one-time or recurring prompts while a remote environment is connected (Scheduling). A clock, not a message you type.
• Channels — native Slack (and Telegram / Discord paths in docs) so the same agent is a coworker in the room you already use (Quickstart step 6). A channel, not the ADE.

Web app (chat.letta.com) and letta CLI are one agent harness. Agent SDK, MCP, and npm i -g @letta-ai/letta-code are install / SDK. Letta Auto quotas and storage MiB are billing.

Who it's for

Best fit: engineers who will run the CLI or the web app and already have an API key or a coding plan.

Pricing

Verified 2026-10-22 (Asia/Shanghai) from letta.com/pricing and the Apache-2.0 LICENSE on the repo cover.

• Software — Apache-2.0. License fee $0.
• Free (personal) — $0/month. Limited agents; 5 MiB per memory repository; limited Letta Auto; BYOK / external coding plans.
• Pro (personal) — $20/month. Letta Auto weekly + monthly quota; pay-as-you-go overage; up to 20 stateful agents; 50 MiB per memory repository; remote sandboxes.
• Teams / Enterprise — shared agents and permissions; contact support@letta.com for per-seat.
• Developer / API — usage-based credits (model tokens + tool CPU). No public seat dollar on that card.

Help-style “$100 / $200 power-user” notes on the same page are usage estimates, not plan cards. Do not list them as SKUs.

Limitations / costs

• You bring the model bill on Free. BYOK / ChatGPT / Kimi / Z.AI plans are yours.
• Free is limited agents + 5 MiB. Pro is the first card with 20 agents and remote sandboxes.
• Library + hosted app, not a paper-review site. For a manuscript reviewer, see Paperpal.
• CLI/web are one harness. Do not count them as two products.

Alternatives

• Claude Code — Anthropic’s coding agent in the terminal.
• Open Hands — open-source software-engineering agent.
• Mem0 — memory layer you attach to your own agent.

Official tutorial

Official Letta channel video: Building an AI writing assistant (stateful agent + memory blocks).

Written path: Quickstart (web app or npm i -g @letta-ai/letta-code).

Website

https://www.letta.com

Repository

https://github.com/letta-ai/letta

Source

Catalog row curated for AI Tools Nav. Cover is the official letta-ai/letta GitHub file list (Apache-2.0). Dollars checked on letta.com/pricing (Free $0; Pro $20/mo; Teams/API contact or usage). Tutorial oEmbed author: Letta.

Last verified

2026-10-22 (Asia/Shanghai) editorial check.