These tools integrates with

OpenAI APIvsLetta

GPT-5 era models, embeddings, and Responses API from OpenAI versus Stateful agents with long-term memory — formerly MemGPT

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Choose OpenAI API when…

  • •You need the broadest ecosystem and most integrations
  • •GPT-4 or o-series reasoning models are required
  • •Assistants API, fine-tuning, or batch API are needed

Choose Letta when…

  • •need agents with persistent cross-session memory
  • •context window length is limiting your application
  • •building personal assistants or long-running agents

Side-by-side comparison

Field
OpenAI API
Letta
Category
LLM Infrastructure
Agent Frameworks
Type
Commercial
Open Source
Free Tier
✗ No
✓ Yes
Pricing Plans
API: Per token
Open Source: FreeCloud: $20/mo
GitHub Stars
—
⭐ 13,200
Health
—
●100 — Active

OpenAI API

API access to GPT-5, GPT-5.5, o3/o4 reasoning models, and the Responses API; plus embeddings, image, audio, and Realtime endpoints. The most widely deployed LLM API in production.

Website ↗

Letta

Letta (formerly MemGPT) is an open-source framework for building stateful AI agents with persistent, editable memory. Agents remember conversations across sessions, search their own memory, and update their knowledge over time — solving context window limitations.

Website ↗GitHub ↗

Only OpenAI API (39)

CrewAIAutoGenLlamaIndexLangChainPydanticAIsmolagentsAgnoMastraLiteLLMPortKey

Only Letta (2)

LangGraphOpenAI API

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See how OpenAI API and Letta fit into the bigger picture — 235 tools, 543 relationships, all mapped.

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