Stateful agent framework and cloud from the MemGPT team — agents that actually remember across sessions.
Stateful agent framework and cloud from the MemGPT team — agents that actually remember across sessions.
Letta (formerly MemGPT) is the open-source framework and hosted cloud for building agents with persistent, self-editing memory. Where most LLM apps forget everything the moment the context window rolls, Letta gives every agent a durable memory tier — core memory, archival memory, and message buffers — that the model reads and writes via tool calls. The result is agents that remember users across weeks of conversation, learn preferences, and can be paused, resumed, or migrated between models without losing state. Letta ships as a Python/TypeScript SDK, a self-hosted server, and a fully managed cloud at letta.com. The Agent Development Environment (ADE) is a browser IDE for inspecting an agent's memory, tools, and every reasoning step — invaluable for debugging long-running agents. Letta is model-agnostic (OpenAI, Anthropic, local Llama, Ollama), supports MCP for tool integration, and exposes agents through a REST API so they slot into existing backends. The team came out of UC Berkeley's Sky Lab with the original MemGPT paper and has become a de-facto standard for anyone building customer-support agents, personal assistants, or copilots that need to feel like they know you. Free self-hosted; Letta Cloud starts at $20/month with usage-based pricing for hosted agents.
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Letta (formerly MemGPT) offers a distinctive memory-first approach where agents manage persistent state instead of relying only on prompt reconstruction. The self-editing memory model is powerful for long-running assistants, but it is a developer-oriented platform with operational and evaluation complexity.
Three-tier memory: core memory that stays in context and can be edited by the agent, recall memory for searchable conversation history, and archival memory for long-term vector-style storage.
Use Case:
A personal assistant agent that keeps your current project details in core memory, recent conversations in recall, and years of interaction history in archival memory.
The agent has explicit tools for memory operations such as appending or replacing core memory, inserting archival memory, searching archival memory, and searching conversation history.
Use Case:
An agent that proactively archives important details from a meeting conversation and later retrieves them when the user asks about action items.
Agents run as persistent server-backed entities with REST API endpoints. State is maintained between API calls without requiring the client to rebuild full context on every request.
Use Case:
Deploying a fleet of customer-specific agents where each agent remembers its customer's history and preferences across months of interactions.
Visual interface for creating agents, defining core memory blocks, attaching tools, configuring LLM providers, and testing agent interactions before deploying through the API.
Use Case:
A product manager defining a new support agent's personality, knowledge base, and tools through a visual interface before handing it to engineering for production integration.
Agents can participate in multi-agent workflows where each agent maintains independent state and memory while collaborating through tool and message patterns.
Use Case:
A research agent that gathers information and sends summarized findings to an analysis agent, which then passes conclusions to a report-writing agent.
Agents can be equipped with custom tools and connected to external data sources that populate archival memory. Tools are defined for the agent to call during conversations or workflows.
Use Case:
Equipping a sales agent with CRM lookup tools and product database access that it searches autonomously when customers ask about pricing or features.
Free
$20/month
Custom
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Letta's current site highlights recent work including Context Constitution, Context Repositories for git-based memory in coding agents, Continual Learning improvements, Letta Code, Letta Auto, AgentFile portability, and expanded platform APIs for stateful agents.
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