Letta
Letta (formerly MemGPT) is a stateful AI agents platform built around long-term memory, tool execution, and multi-agent coordination. The Letta REST API exposes 239 endpoints across 36 public resource categories — agents, memory blocks, archival memory, sources (RAG), custom tools (sandboxed/client-side/MCP), MCP servers, multi-agent groups, identities, runs, scheduled messages, and a streaming voice-mode endpoint. Open-source server (Apache-2.0, 22.9k+ stars) is available on GitHub; Letta Cloud is the managed offering; the Agent Development Environment (ADE) provides a web UI for inspecting context windows, memory blocks, and run history. Python and TypeScript SDKs ship alongside the REST API, and the open `.af` agent file format lets agents migrate between deployments.
Letta publishes 40 APIs on the APIs.io network, including Admin API, Agents API, Archives API, and 37 more. Tagged areas include AI, Agents, Stateful Agents, Memory, and MemGPT.
The Letta catalog on APIs.io includes 1 JSON-LD context and 1 Spectral governance ruleset.
Letta’s developer surface includes authentication, engineering blog, documentation, GitHub presence, pricing, and 17 more developer resources.
Kin Score
Kin Score
How this is scored →scored 2026-07-28 · rubric v0.6
APIs 41
Individual APIs this provider publishes, each with its own machine-readable definition.
Letta Code
Letta's memory-first coding agent — a CLI plus a desktop app (and an action for GitHub repos). "The memory-first coding agent that remembers and learns." Builds on the Letta Cod...
Letta Admin API
Administrative operations (org / billing / policy).
Letta Agents API
Create, list, modify, export, and delete stateful agents with memory and tools.
Letta Archives API
Manage archival memory archives and passages (RAG-style long-term store).
Letta Blocks API
Manage in-context memory blocks (core memory) shared across agents.
Letta Chat API
Chat operations.
Letta Client-Side Access Tokens API
Mint short-lived client-side access tokens for browser/mobile use.
Letta Conversations API
Conversational session threads anchored to an agent.
Letta Device Storage API
Per-device storage for the Letta Code SDK and ADE.
Letta Embeddings API
List configured embedding models.
Letta Environments API
Environment variables and configuration scoped to agents/tools.
Letta Feeds API
Subscribed feeds that drive agents.
Letta Folders API
Organize agents and resources into folders.
Letta Groups API
Coordinate multi-agent groups (supervisor/worker, round-robin, sleep-time).
Letta Health API
Service health/readiness endpoint.
Letta Identities API
Map external user identities to agents and memory contexts.
Letta Internal Agents API
Internal Agents operations.
Letta Internal Blocks API
Internal Blocks operations.
Letta Internal Runs API
Internal Runs operations.
Letta Internal Templates API
Internal Templates operations.
Letta Jobs API
Manage long-running background jobs (e.g., file ingestion).
Letta LLMs API
List available LLM models and configurations.
Letta MCP Servers API
Register external Model Context Protocol servers and expose their tools to agents.
Letta Memory Files API
Memory-mapped file resources attached to agents.
Letta Messages API
Send messages, list message history, search, and batch operations.
Letta Metadata API
Service/runtime metadata.
Letta Models API
List available chat and embedding models exposed by configured providers.
Letta Passages API
Individual archival memory passages (chunked context).
Letta Pipelines API
Composable agent pipelines.
Letta Projects API
Project-level scoping for agents and resources.
Letta Providers API
Configure LLM provider credentials (OpenAI, Anthropic, Azure, Ollama, etc.).
Letta Runs API
Inspect and manage agent runs (executions of an agent in response to a message).
Letta Sandboxes API
Manage code-execution sandboxes used by sandbox tools.
Letta Scheduled Messages API
Schedule one-time or recurring messages to drive agents over time.
Letta Sources API
Manage data sources (files, URLs) used to populate agent archival memory.
Letta Steps API
Per-step traces of an agent run.
Letta Tag API
Tag-based filtering metadata.
Letta Telemetry API
Run-step traces and observability data.
Letta Templates API
Reusable agent templates for instantiation.
Letta Tools API
Register and execute custom tools (sandboxed Python, client-side, MCP).
Letta Voice API
Voice (low-latency) chat completions endpoint for agents.
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Open Collections 1
Open, tool-agnostic API collections (OpenAPI-derived and Bruno).
Letta API
OPEN COLLECTIONPricing Plans 1
Published pricing tiers and plan structures.
Letta Plans Pricing
PLANSRate Limits 1
Documented rate limits and quota policies.
Letta Rate Limits
RATE LIMITSFinOps 1
Cost, billing, and metering signals for API financial operations.
Letta Finops
FINOPSSemantic Vocabularies 1
JSON-LD contexts and semantic vocabularies used across these APIs.
Letta Context
JSON-LDSpectral Rules 1
Spectral governance rulesets for linting and validating these APIs.
Letta API Rules
SPECTRALJSON Schema 349
Standalone JSON Schema definitions for this provider's data models.
AgentState
JSON SCHEMAAgentEnvironmentVariable
JSON SCHEMAAgentFileAttachment
JSON SCHEMAAgentFileSchema
JSON SCHEMAAgentState
JSON SCHEMAAgentType
JSON SCHEMAAnnotation
JSON SCHEMAAnnotationURLCitation
JSON SCHEMAAnthropicModelSettings
JSON SCHEMAAnthropicThinking
JSON SCHEMAApprovalCreate
JSON SCHEMAApprovalRequestMessage
JSON SCHEMAApprovalResponseMessage
JSON SCHEMAApprovalReturn
JSON SCHEMAArchivalMemorySearchResponse
JSON SCHEMAArchivalMemorySearchResult
JSON SCHEMAArchive
JSON SCHEMAArchiveCreateRequest
JSON SCHEMAArchiveUpdateRequest
JSON SCHEMAAssistantMessage
JSON SCHEMAAssistantMessageListResult
JSON SCHEMAAudio
JSON SCHEMAAuthRequest
JSON SCHEMAAuthResponse
JSON SCHEMAAzureModelSettings
JSON SCHEMABase64Image
JSON SCHEMABasetenModelSettings
JSON SCHEMABaseToolRuleSchema
JSON SCHEMABatchJob
JSON SCHEMABedrockModelSettings
JSON SCHEMABillingContext
JSON SCHEMABlock
JSON SCHEMABlockResponse
JSON SCHEMABlockSchema
JSON SCHEMABlockUpdate
JSON SCHEMABody_export_agent
JSON SCHEMABody_import_agent
JSON SCHEMABody_upload_file_to_folder
JSON SCHEMABody_upload_file_to_source
JSON SCHEMACancelAgentRunRequest
JSON SCHEMAChatCompletion
JSON SCHEMAChatCompletionAssistantMessageParam
JSON SCHEMAChatCompletionAudio
JSON SCHEMAChatCompletionContentPartImageParam
JSON SCHEMAChatCompletionContentPartInputAudioParam
JSON SCHEMAChatCompletionContentPartRefusalParam
JSON SCHEMAChatCompletionContentPartTextParam
JSON SCHEMAChatCompletionDeveloperMessageParam
JSON SCHEMAChatCompletionFunctionMessageParam
JSON SCHEMAChatCompletionMessage
JSON SCHEMAChatCompletionMessageCustomToolCall
JSON SCHEMAChatCompletionMessageCustomToolCallParam
JSON SCHEMAChatCompletionMessageFunctionToolCall
JSON SCHEMAChatCompletionMessageFunctionToolCall
JSON SCHEMAChatCompletionMessageFunctionToolCallParam
JSON SCHEMAChatCompletionRequest
JSON SCHEMAChatCompletionSystemMessageParam
JSON SCHEMAChatCompletionToolMessageParam
JSON SCHEMAChatCompletionUserMessageParam
JSON SCHEMAChatGPTOAuthModelSettings
JSON SCHEMAChatGPTOAuthReasoning
JSON SCHEMAChildToolRule
JSON SCHEMAChildToolRuleSchema
JSON SCHEMAChoice
JSON SCHEMAClientSkillSchema
JSON SCHEMAClientToolSchema
JSON SCHEMACodeInput
JSON SCHEMACompactionResponse
JSON SCHEMACompactionSettings
JSON SCHEMACompactionSettings
JSON SCHEMACompactionStats
JSON SCHEMAComparisonOperator
JSON SCHEMACompletionTokensDetails
JSON SCHEMACompletionUsage
JSON SCHEMAConditionalToolRule
JSON SCHEMAConditionalToolRuleSchema
JSON SCHEMAContextWindowOverview
JSON SCHEMAContinueToolRule
JSON SCHEMAConversation
JSON SCHEMAConversationMessageRequest
JSON SCHEMACoreMemoryBlockSchema
JSON SCHEMACreateAgentRequest
JSON SCHEMACreateArchivalMemory
JSON SCHEMACreateBatch
JSON SCHEMACreateBlock
JSON SCHEMACreateConversation
JSON SCHEMACreateMCPServerRequest
JSON SCHEMACreateSSEMCPServer
JSON SCHEMACreateStdioMCPServer
JSON SCHEMACreateStreamableHTTPMCPServer
JSON SCHEMACustom
JSON SCHEMACustom
JSON SCHEMADeepseekModelSettings
JSON SCHEMADeleteDeploymentResponse
JSON SCHEMADeploymentEntity
JSON SCHEMADuplicateFileHandling
JSON SCHEMADynamicManager
JSON SCHEMADynamicManagerSchema
JSON SCHEMADynamicManagerUpdate
JSON SCHEMAE2BSandboxConfig
JSON SCHEMAEmbeddingConfig
JSON SCHEMAEmbeddingConfig
JSON SCHEMAEmbeddingModel
JSON SCHEMAEventMessage
JSON SCHEMAExportAgentRequest
JSON SCHEMAFeedbackType
JSON SCHEMAFile
JSON SCHEMAFileAgentSchema
JSON SCHEMAFileBlock
JSON SCHEMAFileFile
JSON SCHEMAFileMetadata
JSON SCHEMAFileProcessingStatus
JSON SCHEMAFileSchema
JSON SCHEMAFileStats
JSON SCHEMAFolder
JSON SCHEMAFunction
JSON SCHEMAFunctionCall
JSON SCHEMAFunctionCall
JSON SCHEMAFunctionDefinition
JSON SCHEMAFunctionTool
JSON SCHEMAGeminiThinkingConfig
JSON SCHEMAGenerateRequest
JSON SCHEMAGenerateResponse
JSON SCHEMAGenerateToolInput
JSON SCHEMAGenerateToolOutput
JSON SCHEMAGoogleAIModelSettings
JSON SCHEMAGoogleVertexModelSettings
JSON SCHEMAGroqModelSettings
JSON SCHEMAGroup
JSON SCHEMAGroupCreate
JSON SCHEMAGroupSchema
JSON SCHEMAGroupUpdate
JSON SCHEMAHealth
JSON SCHEMAHiddenReasoningMessage
JSON SCHEMAHTTPValidationError
JSON SCHEMAIdentity
JSON SCHEMAIdentityCreate
JSON SCHEMAIdentityProperty
JSON SCHEMAIdentityPropertyType
JSON SCHEMAIdentityType
JSON SCHEMAIdentityUpdate
JSON SCHEMAIdentityUpsert
JSON SCHEMAImageContent
JSON SCHEMAImageURL
JSON SCHEMAImportedAgentsResponse
JSON SCHEMAInitToolRule
JSON SCHEMAInputAudio
JSON SCHEMAInternalTemplateAgentCreate
JSON SCHEMAInternalTemplateBlockCreate
JSON SCHEMAInternalTemplateGroupCreate
JSON SCHEMAJob
JSON SCHEMAJobStatus
JSON SCHEMAJobType
JSON SCHEMAJsonObjectResponseFormat
JSON SCHEMAJsonSchemaResponseFormat
JSON SCHEMAAgentSchema
JSON SCHEMAMessageSchema
JSON SCHEMAToolSchema
JSON SCHEMAToolReturn
JSON SCHEMAToolExecuteRequest
JSON SCHEMAUpdateSSEMCPServer
JSON SCHEMAUpdateStdioMCPServer
JSON SCHEMAUpdateStreamableHTTPMCPServer
JSON SCHEMAUpdateSSEMCPServer
JSON SCHEMAUpdateStdioMCPServer
JSON SCHEMAUpdateStreamableHTTPMCPServer
JSON SCHEMAToolReturn
JSON SCHEMAToolReturn
JSON SCHEMAChatCompletionTokenLogprob
JSON SCHEMAChoiceLogprobs
JSON SCHEMATopLogprob
JSON SCHEMAAgentSchema
JSON SCHEMAMessageSchema
JSON SCHEMAToolSchema
JSON SCHEMACompactionRequest
JSON SCHEMACompactionRequest
JSON SCHEMAToolExecuteRequest
JSON SCHEMALettaAssistantMessageContentUnion
JSON SCHEMALettaAsyncRequest
JSON SCHEMALettaBatchMessages
JSON SCHEMALettaBatchRequest
JSON SCHEMALettaErrorMessage
JSON SCHEMALettaImage
JSON SCHEMALettaMessageContentUnion
JSON SCHEMALettaMessageUnion
JSON SCHEMALettaPing
JSON SCHEMALettaRequest
JSON SCHEMALettaRequestConfig
JSON SCHEMALettaResponse
JSON SCHEMALettaStopReason
JSON SCHEMALettaStreamingRequest
JSON SCHEMALettaStreamingResponse
JSON SCHEMALettaToolReturnContentUnion
JSON SCHEMALettaUsageStatistics
JSON SCHEMALettaUserMessageContentUnion
JSON SCHEMAListDeploymentEntitiesResponse
JSON SCHEMALLMConfig
JSON SCHEMALLMConfig
JSON SCHEMALocalSandboxConfig
JSON SCHEMAManagerType
JSON SCHEMAMaxCountPerStepToolRule
JSON SCHEMAMaxCountPerStepToolRuleSchema
JSON SCHEMAMCPServerSchema
JSON SCHEMAMCPServerType
JSON SCHEMAMCPTool
JSON SCHEMAMCPToolHealth
JSON SCHEMAMemory
JSON SCHEMAMessage
JSON SCHEMAMessageCreate
JSON SCHEMAMessageRole
JSON SCHEMAMessageSearchCacheWarmScope
JSON SCHEMAMessageSearchRequest
JSON SCHEMAMessageSearchResult
JSON SCHEMAMessageType
JSON SCHEMAModalSandboxConfig
JSON SCHEMAModel
JSON SCHEMAModifyApprovalRequest
JSON SCHEMAModifyFeedbackRequest
JSON SCHEMANpmRequirement
JSON SCHEMAOmittedReasoningContent
JSON SCHEMAChoiceLogprobs
JSON SCHEMAFunction
JSON SCHEMAChatCompletionTokenLogprob
JSON SCHEMATopLogprob
JSON SCHEMAOpenAIModelSettings
JSON SCHEMAOpenAIReasoning
JSON SCHEMAOpenRouterModelSettings
JSON SCHEMAOrganization
JSON SCHEMAOrganizationCreate
JSON SCHEMAOrganizationSourcesStats
JSON SCHEMAOrganizationUpdate
JSON SCHEMAPaginatedAgentFiles
JSON SCHEMAParameterProperties
JSON SCHEMAParametersSchema
JSON SCHEMAParentToolRule
JSON SCHEMAPassage
JSON SCHEMAPassageBatchCreateRequest
JSON SCHEMAPassageCreateRequest
JSON SCHEMAPassageSearchRequest
JSON SCHEMAPassageSearchResult
JSON SCHEMAPipRequirement
JSON SCHEMAPromptTokensDetails
JSON SCHEMAProvider
JSON SCHEMAProviderCategory
JSON SCHEMAProviderCheck
JSON SCHEMAProviderCreate
JSON SCHEMAProviderTrace
JSON SCHEMAProviderType
JSON SCHEMAProviderUpdate
JSON SCHEMAReasoningContent
JSON SCHEMAReasoningMessage
JSON SCHEMAReasoningMessageListResult
JSON SCHEMARedactedReasoningContent
JSON SCHEMARequiredBeforeExitToolRule
JSON SCHEMARequiresApprovalToolRule
JSON SCHEMAResetMessagesRequest
JSON SCHEMARetrieveStreamRequest
JSON SCHEMARoundRobinManager
JSON SCHEMARoundRobinManagerUpdate
JSON SCHEMARun
JSON SCHEMARunMetrics
JSON SCHEMARunStatus
JSON SCHEMASandboxConfig
JSON SCHEMASandboxConfigCreate
JSON SCHEMASandboxConfigUpdate
JSON SCHEMASandboxEnvironmentVariable
JSON SCHEMASandboxEnvironmentVariableCreate
JSON SCHEMASandboxEnvironmentVariableUpdate
JSON SCHEMASandboxType
JSON SCHEMASearchAllMessagesRequest
JSON SCHEMASearchCacheWarmRequest
JSON SCHEMASearchCacheWarmResponse
JSON SCHEMASGLangModelSettings
JSON SCHEMASkillSchema
JSON SCHEMASleeptimeManager
JSON SCHEMASleeptimeManagerSchema
JSON SCHEMASleeptimeManagerUpdate
JSON SCHEMASource
JSON SCHEMASourceCreate
JSON SCHEMASourceSchema
JSON SCHEMASourceStats
JSON SCHEMASourceUpdate
JSON SCHEMASSEMCPServer
JSON SCHEMASSEServerConfig
JSON SCHEMAStdioMCPServer
JSON SCHEMAStdioServerConfig
JSON SCHEMAStep
JSON SCHEMAStepMetrics
JSON SCHEMAStepStatus
JSON SCHEMAStopReasonType
JSON SCHEMAStreamableHTTPMCPServer
JSON SCHEMAStreamableHTTPServerConfig
JSON SCHEMASummarizedReasoningContent
JSON SCHEMASummarizedReasoningContentPart
JSON SCHEMASummaryMessage
JSON SCHEMASupervisorManager
JSON SCHEMASupervisorManagerSchema
JSON SCHEMASupervisorManagerUpdate
JSON SCHEMASystemMessage
JSON SCHEMASystemMessageListResult
JSON SCHEMATagSchema
JSON SCHEMATerminalToolRule
JSON SCHEMATextContent
JSON SCHEMATextResponseFormat
JSON SCHEMATogetherModelSettings
JSON SCHEMATool
JSON SCHEMAToolAnnotations
JSON SCHEMAToolCall
JSON SCHEMAToolCallContent
JSON SCHEMAToolCallDelta
JSON SCHEMAToolCallMessage
JSON SCHEMAToolCallNode
JSON SCHEMAToolCreate
JSON SCHEMAToolEnvVarSchema
JSON SCHEMAToolExecutionResult
JSON SCHEMAToolJSONSchema
JSON SCHEMAToolReturnContent
JSON SCHEMAToolReturnCreate
JSON SCHEMAToolReturnMessage
JSON SCHEMAToolRunFromSource
JSON SCHEMAToolSearchRequest
JSON SCHEMAToolSearchResult
JSON SCHEMAToolType
JSON SCHEMAToolUpdate
JSON SCHEMATurnTokenData
JSON SCHEMAUpdateAgent
JSON SCHEMAUpdateAssistantMessage
JSON SCHEMAUpdateConversation
JSON SCHEMAUpdateMCPServerRequest
JSON SCHEMAUpdateReasoningMessage
JSON SCHEMAUpdateSystemMessage
JSON SCHEMAUpdateUserMessage
JSON SCHEMAUrlImage
JSON SCHEMAUsageStatistics
JSON SCHEMAUsageStatisticsCompletionTokenDetails
JSON SCHEMAUsageStatisticsPromptTokenDetails
JSON SCHEMAUser
JSON SCHEMAUserCreate
JSON SCHEMAUserMessage
JSON SCHEMAUserMessageListResult
JSON SCHEMAUserUpdate
JSON SCHEMAValidationError
JSON SCHEMAVectorDBProvider
JSON SCHEMAVoiceSleeptimeManager
JSON SCHEMAVoiceSleeptimeManagerSchema
JSON SCHEMAVoiceSleeptimeManagerUpdate
JSON SCHEMAXAIModelSettings
JSON SCHEMAZAIModelSettings
JSON SCHEMAZAIThinking
JSON SCHEMAScroll for all 349
JSON Structure 15
JSON Structure definitions describing this provider's data shapes.
Letta Agent Structure
JSON STRUCTURELetta Archive Structure
JSON STRUCTURELetta Block Structure
JSON STRUCTURELetta Embedding Config Structure
JSON STRUCTURELetta Group Structure
JSON STRUCTURELetta Identity Structure
JSON STRUCTURELetta Job Structure
JSON STRUCTURELetta Llm Config Structure
JSON STRUCTURELetta Message Structure
JSON STRUCTURELetta Passage Structure
JSON STRUCTURELetta Provider Structure
JSON STRUCTURELetta Run Structure
JSON STRUCTURELetta Source Structure
JSON STRUCTURELetta Structure
JSON STRUCTURELetta Tool Structure
JSON STRUCTUREScroll for all 15
Examples 29
Example request and response payloads for these APIs.
Letta Agent Payload Example
EXAMPLELetta Block Payload Example
EXAMPLELetta Create Agent Example
EXAMPLELetta Create Source Example
EXAMPLELetta Create Tool Example
EXAMPLELetta Group Payload Example
EXAMPLELetta List Agents Example
EXAMPLELetta List Runs Example
EXAMPLELetta List Tools Example
EXAMPLELetta Retrieve Agent Example
EXAMPLELetta Retrieve Run Example
EXAMPLELetta Run Payload Example
EXAMPLELetta Source Payload Example
EXAMPLELetta Tool Payload Example
EXAMPLEScroll for all 29
Security Posture 2
Authentication, domain security, vulnerability disclosure, and trust-center signals.
Agentic Access 1
Recommended x-agentic-access execution contracts for AI agents.
Resources
Get Started 1
Portal, sign-up, and the first successful call
Documentation 1
Reference material describing how the API behaves
Agent Surfaces 3
MCP servers, agent skills, and machine-readable catalogs
Design & Contract 3
Pagination, idempotency, versioning, errors, and events
Build 4
SDKs, sample code, and the tooling you integrate with
Access & Security 2
Authentication, authorization, and security posture
Operate 1
Status, limits, changes, and where to get help
Commercial 3
Pricing, plans, and the legal terms of use
Company 3
The organization behind the API
Other 1
Properties that don't map to a standard resource type