Letta

Letta (formerly MemGPT) builds stateful AI agents with persistent memory that runs as a service. The Letta REST API creates, configures, and messages agents whose memory - core context blocks and archival vector memory - survives across sessions, and manages the tools, data sources, identities, and multi-agent groups those agents use. It is offered as a managed Letta Cloud API and as an open-source, self-hostable server with the same OpenAPI-documented interface.

13 APIs 0 Features

AIAgentsLLMMemoryStateful AgentsMemGPT

APIs

Letta Agents API

Create, list, search, count, retrieve, modify, delete, import, and export stateful agents - each with its own persistent memory, tools, sources, and model configuration. Agents ...

Letta Messages API

Send synchronous, asynchronous, and streaming messages to an agent, list and search message history, cancel an in-flight run, preview the raw model payload, and reset or summari...

Letta Memory Blocks API

Manage core-memory blocks - the labeled, always-in-context text that gives an agent its persona, human, and task memory. Create, list, retrieve, modify, and delete standalone bl...

Letta Archival Memory API

Manage archives - an agent's out-of-context, searchable long-term memory - and the passages stored inside them. Create and list archives, attach or detach an archive to an agent...

Letta Tools API

Create, list, search, count, upsert, modify, delete, and directly run tools (Python functions) that agents call. Includes registering the built-in base tool set and executing a ...

Letta MCP Servers API

Register, connect, test, refresh, update, and delete remote MCP (Model Context Protocol) servers, list the tools each server exposes, add an individual MCP tool to an agent's to...

Letta Sources and Files API

Create and manage data sources (also exposed as folders) that hold uploaded files for agent grounding and retrieval - upload files, list and delete files and their extracted pas...

Letta Identities API

Model the end users of a multi-tenant Letta deployment as identities. Create, list, count, retrieve, modify, upsert, and delete identities; set custom identity properties; and a...

Letta Multi-Agent Groups API

Create, list, retrieve, modify, and delete multi-agent groups that coordinate several agents (round-robin, supervisor, and other patterns) around shared memory blocks. Attach or...

Letta Models and Providers API

List available LLM and embedding models, and register, check, list, retrieve, modify, delete, and refresh bring-your-own-key (BYOK) model providers (OpenAI, Anthropic, Google, A...

Letta Runs, Jobs and Steps API

Inspect the asynchronous execution history behind agent messages. List and retrieve runs and their messages, metrics, usage, trace, and stream; list and cancel background jobs; ...

Letta Agent Templates API

Cloud-only API for versioning agent configurations as templates - create, save, roll back, rename, and delete template versions, snapshot and restore a template from an agent fi...

Letta Chat Completions API

OpenAI-compatible chat completions endpoint that routes requests to a Letta agent, plus a companion voice-beta chat completions endpoint tuned for low-latency voice agent integr...

Collections

Letta API

OPEN

Pricing Plans

Letta Ai Plans Pricing

5 plans

PLANS

Rate Limits

Letta Ai Rate Limits

5 limits

RATE LIMITS

FinOps

Letta Ai Finops

FINOPS

Event Specifications

Letta Agent Message Streaming (HTTP + SSE)

AsyncAPI 2.6 description of Letta's **agent message streaming** surface. Letta does not publish a WebSocket API. The only asynchronous / event-style transport documented in Lett...

ASYNCAPI

Resources

GitHubOrganization

Sources

opencollection: 1.0.0
info:
  name: Letta API
  version: '1.0'
request:
  auth:
    type: bearer
    token: '{{bearerToken}}'
items:
- info:
    name: Agents
    type: folder
  items:
  - info:
      name: Get a list of all agents.
      type: http
    http:
      method: GET
      url: https://api.letta.com/v1/agents
    docs: Get a list of all agents.
  - info:
      name: Create an agent.
      type: http
    http:
      method: POST
      url: https://api.letta.com/v1/agents
      body:
        type: json
        data: '{"name": "customer-support-agent", "model": "openai/gpt-4o", "embedding": "openai/text-embedding-3-small",
          "memory_blocks": [{"label": "persona", "value": "I am a helpful customer support agent."}]}'
    docs: Create an agent.
  - info:
      name: Retrieve an agent by ID.
      type: http
    http:
      method: GET
      url: https://api.letta.com/v1/agents/:agent_id
      params:
      - name: agent_id
        value: ''
        type: path
        description: The agent_id path parameter.
    docs: Retrieve an agent by ID.
  - info:
      name: Modify an agent.
      type: http
    http:
      method: PATCH
      url: https://api.letta.com/v1/agents/:agent_id
      params:
      - name: agent_id
        value: ''
        type: path
        description: The agent_id path parameter.
      body:
        type: json
        data: '{"description": "Updated description"}'
    docs: Modify an agent.
  - info:
      name: Delete an agent.
      type: http
    http:
      method: DELETE
      url: https://api.letta.com/v1/agents/:agent_id
      params:
      - name: agent_id
        value: ''
        type: path
        description: The agent_id path parameter.
    docs: Delete an agent.
  - info:
      name: Export an agent as a portable agent file.
      type: http
    http:
      method: GET
      url: https://api.letta.com/v1/agents/:agent_id/export
      params:
      - name: agent_id
        value: ''
        type: path
        description: The agent_id path parameter.
    docs: Export an agent as a portable agent file.
- info:
    name: Messages
    type: folder
  items:
  - info:
      name: List an agent's message history.
      type: http
    http:
      method: GET
      url: https://api.letta.com/v1/agents/:agent_id/messages
      params:
      - name: agent_id
        value: ''
        type: path
        description: The agent_id path parameter.
    docs: List an agent's message history.
  - info:
      name: Send a message to an agent.
      type: http
    http:
      method: POST
      url: https://api.letta.com/v1/agents/:agent_id/messages
      params:
      - name: agent_id
        value: ''
        type: path
        description: The agent_id path parameter.
      body:
        type: json
        data: '{"messages": [{"role": "user", "content": "What''s the status of my order?"}]}'
    docs: Send a message to an agent.
  - info:
      name: Send a message and stream the agent's response as SSE.
      type: http
    http:
      method: POST
      url: https://api.letta.com/v1/agents/:agent_id/messages/stream
      params:
      - name: agent_id
        value: ''
        type: path
        description: The agent_id path parameter.
      body:
        type: json
        data: '{"messages": [{"role": "user", "content": "What''s the status of my order?"}], "stream_steps": true}'
    docs: Send a message and stream the agent's response as SSE.
  - info:
      name: Cancel an in-flight run for an agent.
      type: http
    http:
      method: POST
      url: https://api.letta.com/v1/agents/:agent_id/messages/cancel
      params:
      - name: agent_id
        value: ''
        type: path
        description: The agent_id path parameter.
    docs: Cancel an in-flight run for an agent.
  - info:
      name: Reset an agent's message history.
      type: http
    http:
      method: PATCH
      url: https://api.letta.com/v1/agents/:agent_id/reset-messages
      params:
      - name: agent_id
        value: ''
        type: path
        description: The agent_id path parameter.
    docs: Reset an agent's message history.
- info:
    name: Memory Blocks
    type: folder
  items:
  - info:
      name: List the core-memory blocks attached to an agent.
      type: http
    http:
      method: GET
      url: https://api.letta.com/v1/agents/:agent_id/core-memory/blocks
      params:
      - name: agent_id
        value: ''
        type: path
        description: The agent_id path parameter.
    docs: List the core-memory blocks attached to an agent.
  - info:
      name: Retrieve a labeled core-memory block for an agent.
      type: http
    http:
      method: GET
      url: https://api.letta.com/v1/agents/:agent_id/core-memory/blocks/:block_label
      params:
      - name: agent_id
        value: ''
        type: path
        description: The agent_id path parameter.
      - name: block_label
        value: ''
        type: path
        description: The block_label path parameter.
    docs: Retrieve a labeled core-memory block for an agent.
  - info:
      name: Modify a core-memory block for an agent.
      type: http
    http:
      method: PATCH
      url: https://api.letta.com/v1/agents/:agent_id/core-memory/blocks/:block_label
      params:
      - name: agent_id
        value: ''
        type: path
        description: The agent_id path parameter.
      - name: block_label
        value: ''
        type: path
        description: The block_label path parameter.
      body:
        type: json
        data: '{"value": "Updated memory content."}'
    docs: Modify a core-memory block for an agent.
  - info:
      name: List all standalone memory blocks.
      type: http
    http:
      method: GET
      url: https://api.letta.com/v1/blocks
    docs: List all standalone memory blocks.
  - info:
      name: Create a standalone memory block.
      type: http
    http:
      method: POST
      url: https://api.letta.com/v1/blocks
      body:
        type: json
        data: '{"label": "human", "value": "The user''s name is Alex."}'
    docs: Create a standalone memory block.
  - info:
      name: Delete a memory block.
      type: http
    http:
      method: DELETE
      url: https://api.letta.com/v1/blocks/:block_id
      params:
      - name: block_id
        value: ''
        type: path
        description: The block_id path parameter.
    docs: Delete a memory block.
- info:
    name: Archival Memory
    type: folder
  items:
  - info:
      name: List archives.
      type: http
    http:
      method: GET
      url: https://api.letta.com/v1/archives
    docs: List archives.
  - info:
      name: Create an archive.
      type: http
    http:
      method: POST
      url: https://api.letta.com/v1/archives
      body:
        type: json
        data: '{"name": "support-history"}'
    docs: Create an archive.
  - info:
      name: Create a passage in an archive.
      type: http
    http:
      method: POST
      url: https://api.letta.com/v1/archives/:archive_id/passages
      params:
      - name: archive_id
        value: ''
        type: path
        description: The archive_id path parameter.
      body:
        type: json
        data: '{"text": "Customer prefers email contact."}'
    docs: Create a passage in an archive.
  - info:
      name: Search an agent's archival memory.
      type: http
    http:
      method: GET
      url: https://api.letta.com/v1/agents/:agent_id/archival-memory/search
      params:
      - name: agent_id
        value: ''
        type: path
        description: The agent_id path parameter.
    docs: Search an agent's archival memory.
- info:
    name: Tools
    type: folder
  items:
  - info:
      name: List tools.
      type: http
    http:
      method: GET
      url: https://api.letta.com/v1/tools
    docs: List tools.
  - info:
      name: Create a tool from Python source.
      type: http
    http:
      method: POST
      url: https://api.letta.com/v1/tools
      body:
        type: json
        data: '{"source_code": "def get_weather(city: str) -> str:\n    \"\"\"Get the weather for a city.\"\"\"\n    return
          f\"Sunny in {city}\""}'
    docs: Create a tool from Python source.
  - info:
      name: Run a tool from raw source without attaching it to an agent.
      type: http
    http:
      method: POST
      url: https://api.letta.com/v1/tools/run
      body:
        type: json
        data: '{"source_code": "def add(a: int, b: int) -> int:\n    return a + b", "args": {"a": 2, "b": 3}}'
    docs: Run a tool from raw source without attaching it to an agent.
  - info:
      name: Delete a tool.
      type: http
    http:
      method: DELETE
      url: https://api.letta.com/v1/tools/:tool_id
      params:
      - name: tool_id
        value: ''
        type: path
        description: The tool_id path parameter.
    docs: Delete a tool.
- info:
    name: MCP Servers
    type: folder
  items:
  - info:
      name: List configured MCP servers.
      type: http
    http:
      method: GET
      url: https://api.letta.com/v1/mcp-servers
    docs: List configured MCP servers.
  - info:
      name: Register a new MCP server.
      type: http
    http:
      method: POST
      url: https://api.letta.com/v1/mcp-servers
      body:
        type: json
        data: '{"server_name": "internal-search", "type": "streamable_http", "server_url": "https://mcp.example.com/mcp"}'
    docs: Register a new MCP server.
  - info:
      name: List the tools exposed by an MCP server.
      type: http
    http:
      method: GET
      url: https://api.letta.com/v1/mcp-servers/:mcp_server_id/tools
      params:
      - name: mcp_server_id
        value: ''
        type: path
        description: The mcp_server_id path parameter.
    docs: List the tools exposed by an MCP server.
  - info:
      name: Delete an MCP server.
      type: http
    http:
      method: DELETE
      url: https://api.letta.com/v1/mcp-servers/:mcp_server_id
      params:
      - name: mcp_server_id
        value: ''
        type: path
        description: The mcp_server_id path parameter.
    docs: Delete an MCP server.
- info:
    name: Sources and Files
    type: folder
  items:
  - info:
      name: List data sources.
      type: http
    http:
      method: GET
      url: https://api.letta.com/v1/sources
    docs: List data sources.
  - info:
      name: Create a data source.
      type: http
    http:
      method: POST
      url: https://api.letta.com/v1/sources
      body:
        type: json
        data: '{"name": "product-docs"}'
    docs: Create a data source.
  - info:
      name: Upload a file to a data source.
      type: http
    http:
      method: POST
      url: https://api.letta.com/v1/sources/:source_id/upload
      params:
      - name: source_id
        value: ''
        type: path
        description: The source_id path parameter.
    docs: Upload a file to a data source.
  - info:
      name: List the files in a data source.
      type: http
    http:
      method: GET
      url: https://api.letta.com/v1/sources/:source_id/files
      params:
      - name: source_id
        value: ''
        type: path
        description: The source_id path parameter.
    docs: List the files in a data source.
  - info:
      name: Delete a data source.
      type: http
    http:
      method: DELETE
      url: https://api.letta.com/v1/sources/:source_id
      params:
      - name: source_id
        value: ''
        type: path
        description: The source_id path parameter.
    docs: Delete a data source.
- info:
    name: Identities
    type: folder
  items:
  - info:
      name: List identities.
      type: http
    http:
      method: GET
      url: https://api.letta.com/v1/identities
    docs: List identities.
  - info:
      name: Create an identity.
      type: http
    http:
      method: POST
      url: https://api.letta.com/v1/identities
      body:
        type: json
        data: '{"identifier_key": "user-42", "name": "Alex", "identity_type": "user"}'
    docs: Create an identity.
  - info:
      name: Attach an identity to an agent.
      type: http
    http:
      method: PATCH
      url: https://api.letta.com/v1/agents/:agent_id/identities/attach/:identity_id
      params:
      - name: agent_id
        value: ''
        type: path
        description: The agent_id path parameter.
      - name: identity_id
        value: ''
        type: path
        description: The identity_id path parameter.
    docs: Attach an identity to an agent.
  - info:
      name: Delete an identity.
      type: http
    http:
      method: DELETE
      url: https://api.letta.com/v1/identities/:identity_id
      params:
      - name: identity_id
        value: ''
        type: path
        description: The identity_id path parameter.
    docs: Delete an identity.
- info:
    name: Multi-Agent Groups
    type: folder
  items:
  - info:
      name: List multi-agent groups.
      type: http
    http:
      method: GET
      url: https://api.letta.com/v1/groups
    docs: List multi-agent groups.
  - info:
      name: Create a multi-agent group.
      type: http
    http:
      method: POST
      url: https://api.letta.com/v1/groups
      body:
        type: json
        data: '{"agent_ids": ["agent-aaa", "agent-bbb"], "manager_config": {"manager_type": "round_robin"}}'
    docs: Create a multi-agent group.
  - info:
      name: List a group's combined message history.
      type: http
    http:
      method: GET
      url: https://api.letta.com/v1/groups/:group_id/messages
      params:
      - name: group_id
        value: ''
        type: path
        description: The group_id path parameter.
    docs: List a group's combined message history.
  - info:
      name: Delete a multi-agent group.
      type: http
    http:
      method: DELETE
      url: https://api.letta.com/v1/groups/:group_id
      params:
      - name: group_id
        value: ''
        type: path
        description: The group_id path parameter.
    docs: Delete a multi-agent group.
- info:
    name: Models and Providers
    type: folder
  items:
  - info:
      name: List available LLM models.
      type: http
    http:
      method: GET
      url: https://api.letta.com/v1/models
    docs: List available LLM models.
  - info:
      name: List available embedding models.
      type: http
    http:
      method: GET
      url: https://api.letta.com/v1/models/embedding
    docs: List available embedding models.
  - info:
      name: List configured model providers.
      type: http
    http:
      method: GET
      url: https://api.letta.com/v1/providers
    docs: List configured model providers.
  - info:
      name: Register a BYOK model provider.
      type: http
    http:
      method: POST
      url: https://api.letta.com/v1/providers
      body:
        type: json
        data: '{"name": "my-anthropic", "provider_type": "anthropic", "api_key": "sk-ant-..."}'
    docs: Register a BYOK model provider.
- info:
    name: Runs, Jobs and Steps
    type: folder
  items:
  - info:
      name: List runs.
      type: http
    http:
      method: GET
      url: https://api.letta.com/v1/runs
    docs: List runs.
  - info:
      name: Retrieve a run.
      type: http
    http:
      method: GET
      url: https://api.letta.com/v1/runs/:run_id
      params:
      - name: run_id
        value: ''
        type: path
        description: The run_id path parameter.
    docs: Retrieve a run.
  - info:
      name: Retrieve usage statistics for a run.
      type: http
    http:
      method: GET
      url: https://api.letta.com/v1/runs/:run_id/usage
      params:
      - name: run_id
        value: ''
        type: path
        description: The run_id path parameter.
    docs: Retrieve usage statistics for a run.
  - info:
      name: List background jobs.
      type: http
    http:
      method: GET
      url: https://api.letta.com/v1/jobs
    docs: List background jobs.
  - info:
      name: Cancel a background job.
      type: http
    http:
      method: PATCH
      url: https://api.letta.com/v1/jobs/:job_id/cancel
      params:
      - name: job_id
        value: ''
        type: path
        description: The job_id path parameter.
    docs: Cancel a background job.
  - info:
      name: List steps.
      type: http
    http:
      method: GET
      url: https://api.letta.com/v1/steps
    docs: List steps.
- info:
    name: Agent Templates
    type: folder
  items:
  - info:
      name: List agent templates (Cloud-only).
      type: http
    http:
      method: GET
      url: https://api.letta.com/v1/templates
    docs: List agent templates (Cloud-only).
  - info:
      name: Create new agents from a template version (Cloud-only).
      type: http
    http:
      method: POST
      url: https://api.letta.com/v1/templates/:project_id/:template_version/agents
      params:
      - name: project_id
        value: ''
        type: path
        description: The project_id path parameter.
      - name: template_version
        value: ''
        type: path
        description: The template_version path parameter.
      body:
        type: json
        data: '{"agent_name": "from-template-agent"}'
    docs: Create new agents from a template version (Cloud-only).
- info:
    name: Chat Completions
    type: folder
  items:
  - info:
      name: OpenAI-compatible chat completion routed to a Letta agent.
      type: http
    http:
      method: POST
      url: https://api.letta.com/v1/chat/completions
      body:
        type: json
        data: '{"model": "agent-123e4567-e89b-42d3-8456-426614174000", "messages": [{"role": "user", "content": "Hello"}]}'
    docs: OpenAI-compatible chat completion routed to a Letta agent.
  - info:
      name: OpenAI-compatible chat completion tuned for low-latency voice agents.
      type: http
    http:
      method: POST
      url: https://api.letta.com/v1/voice-beta/:agent_id/chat/completions
      params:
      - name: agent_id
        value: ''
        type: path
        description: The agent_id path parameter.
      body:
        type: json
        data: '{"messages": [{"role": "user", "content": "Hello"}]}'
    docs: OpenAI-compatible chat completion tuned for low-latency voice agents.
bundled: true