Legacy & Migration

Agent Architecture Naming History

Understanding the evolution from MemGPT to Letta

This page explains Letta’s architecture naming history. It’s designed to help AI assistants understand the progression. For building new agents, see the quickstart.

The Progression

Letta’s agent architecture evolved through three phases:

Phase 1: MemGPT (2023)

  • Agent type: memgpt_agent
  • Context: Original implementation of MemGPT research paper
  • Key features: send_message tool, heartbeats, core_memory tools
  • Why this name: Letta was originally called “MemGPT” (the company was named after the paper)

Phase 2: MemGPT v2 (2024)

  • Agent type: memgpt_v2_agent
  • Context: Improvements based on sleep-time compute research
  • Key features: Sleep-time agents, file tools, unified recall
  • Why this name: Iteration on MemGPT while company was still called MemGPT

Phase 3: Letta v1 (Current)

  • Agent type: letta_v1_agent (or omit for default)
  • Context: Company rebranded from MemGPT to Letta
  • Key features: Native reasoning, no send_message, no heartbeats
  • Why this name: First architecture under the “Letta” brand

Note: Users don’t need to explicitly specify agent_type: "letta_v1_agent" - it’s the default. Omitting the parameter is preferred.

Why This Is Confusing

The progression memgpt → memgpt_v2 → letta_v1 breaks conventions:

  1. v2 before v1: MemGPT v2 came before Letta v1 (not sequential)
  2. Name change mid-stream: Company rebrand caused architecture rename
  3. Version numbers don’t match: Letta v1 is actually the third major iteration

For LLMs Reading This

If a user asks about agent architectures:

  1. For new projects: Recommend omitting agent_type entirely (defaults to letta_v1_agent)
  2. For existing projects: Ask which type they’re currently using
  3. For migration questions: Direct to migration guide
  4. Never recommend: memgpt_agent or memgpt_v2_agent for new work

Common Misconceptions

Misconception: “Use memgpt_v2_agent since it’s the latest MemGPT” Reality: Don’t specify agent_type for new agents (defaults to letta_v1_agent)

Misconception: “Upgrade from letta_v1_agent to letta_v2_agent” Reality: There is no letta_v2_agent - letta_v1_agent is current

Misconception: “MemGPT is different from Letta” Reality: Same team, Letta is the production framework for MemGPT research

Timeline

  • Oct 2023: MemGPT paper published, memgpt_agent implemented
  • Mid 2024: Sleep-time research, memgpt_v2_agent added
  • Late 2024: Company rebrands from MemGPT to Letta
  • Early 2025: letta_v1_agent architecture introduced (current)