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.
Real signal across most facets with visible, nameable gaps — the contract exists but is thin, or the portal is good while governance and commercial terms are absent.
API Evangelist profiles Letta the way a machine reads it — 23 machine-readable artifacts across 14 APIs, pulled from the provider's own public surface and indexed so a developer, an analyst, or an AI agent can evaluate it against every other provider on the network.
Every provider in the network is reduced to the same set of machine-readable artifacts — OpenAPI contracts, event specifications, GraphQL schemas, runnable collections, pricing and rate-limit signals, security posture, OAuth scopes, and the agent surfaces (MCP servers and skills) that let software drive the API on its own. We profile them because the interface is the part of a company you can actually inspect: it is a truer signal of what a provider does than any marketing page. From those artifacts we compute the Kin Score — Letta scores 48.5/100 (developing), with a separate agent-readiness read of 54/100 (agent ready). The full breakdown is below, followed by every artifact we hold — each card links through to its machine-readable definition on apis.io.
Kin Score
This is the API Evangelist rating — a single, repeatable read computed from the artifacts on this page. Green fill is points earned; the red track is points possible, so every bar shows earned-versus-possible at a glance.
Kin Score
How this is scored →scored 2026-07-27 · rubric v0.5
How we profile Letta
Each block below is one kind of artifact we hold for Letta. For each we say what it is and why it earns a place in the profile, then list every one we've indexed — capped at two rows, scroll within the panel for the rest.
APIs 14
Each API is captured as its own OpenAPI definition — every operation, parameter, and response. This is the single most useful machine-readable description of what an API does, and it's what lets us score, lint, mock, and generate against it without asking the provider for anything.
Individual APIs this provider publishes, each with its own machine-readable definition.
Letta Agent Templates API
Cloud-only versioned agent configuration templates.
Letta Agents API
Stateful agents and their lifecycle.
Letta Archival Memory API
Out-of-context long-term memory archives and passages.
Letta Chat Completions API
OpenAI-compatible chat completions backed by a Letta agent.
Letta Identities API
End users of a multi-tenant Letta deployment.
Letta MCP Servers API
Remote Model Context Protocol tool servers.
Letta Memory Blocks API
Core-memory blocks shared across agents, groups, and identities.
Letta Models and Providers API
Available models and configured BYOK model providers.
Letta Multi-Agent Groups API
Groups of agents coordinating around shared memory.
Letta Runs, Jobs and Steps API
Asynchronous execution history behind agent messages.
Letta Sources and Files API
Uploaded files and folders used for agent grounding and retrieval.
Letta Tag API
The Tag API from Letta — 1 operation(s) for tag.
Letta Tools API
Functions agents can call, including MCP-backed tools.
Letta Voice API
The Voice API from Letta — 1 operation(s) for voice.
Scroll within the panel for all 14 ·
Open Collections 1
Open, tool-agnostic collections carry the same runnable value as Postman without locking you to one client — the portable, forkable form of the same exercise.
Open, tool-agnostic API collections (OpenAPI-derived and Bruno).
Letta API
OPEN COLLECTIONPricing Plans 1
Pricing is part of the interface. Machine-readable plans tell you what a tier costs and includes before you commit — one of the six things the Kin Score reads for commercial clarity.
Published pricing tiers and plan structures.
Rate Limits 1
Rate limits are the difference between a demo that works and a production integration that doesn't fall over. Publishing them is an operational-transparency signal — and a hard requirement for any agent that plans its own throughput.
Documented rate limits and quota policies.
Letta Ai Rate Limits
RATE LIMITSFinOps 1
Cost, billing, and metering signals let a buyer model the financial operations of an API before it's live. We profile them for the same reason we profile pricing: the money is part of the contract.
Cost, billing, and metering signals for API financial operations.
Letta Ai Finops
FINOPSEvent Specifications 1
Not every API is request/response. AsyncAPI describes the event-driven and streaming side — the webhooks and channels — so the asynchronous half of the interface is documented the same way the synchronous half is.
AsyncAPI definitions for this provider's event-driven and streaming APIs.
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...
ASYNCAPISpectral Rules 1
Governance rulesets we run against this provider's specs — the automated checks behind parts of the score. Profiling them makes the quality bar explicit and re-runnable, not a matter of opinion.
Letta API Rules
SPECTRALSecurity Posture 2
Authentication, domain security, vulnerability disclosure, and trust-center signals — the evidence that a provider takes security seriously enough to document it. We profile it because you can't govern what you can't see.
Authentication, domain security, vulnerability disclosure, and trust-center signals.
Agentic Access 1
An x-agentic-access contract marks which operations are safe for an agent to run on its own and which need a human in the loop. It is the difference between an API an agent can use and one it can use safely.
Recommended x-agentic-access execution contracts for AI agents.
Resources
Every other property we hold for Letta — documentation, portals, status pages, policies, and corporate surface — grouped by the job it does, following the integrator's arc from getting started to running in production.
Documentation 1
Reference material describing how the API behaves
Agent Surfaces 1
MCP servers, agent skills, and machine-readable catalogs
Build 1
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 2
Pricing, plans, and the legal terms of use
Company 3
The organization behind the API
← All providers · Data indexed from github.com/api-evangelist/letta-ai · machine-readable index on apis.io