Legacy agent architectures

This documentation covers legacy agent architectures.

For new projects, you should not specify an agent_type parameter. Letta uses the current architecture by default, which provides the best performance with modern reasoning models like GPT-o1 and Claude Sonnet 4.5.

Current Architecture

When you create an agent in Letta today, it uses our latest agent architecture optimized for:

• Full support for native reasoning (via Responses API)
• Compatibility with any LLM (tool calling not required)
• Simpler base system prompt
• Better performance on frontier models

You don’t need to specify an architecture. Just create an agent:

TypeScript

const agent = await client.agents.create({
  model: "openai/gpt-o1",
  embedding: "openai/text-embedding-3-small",
  memory_blocks: [{ label: "persona", value: "I am a helpful assistant." }],
});

Python

agent = client.agents.create(
    model="openai/gpt-o1",
    embedding="openai/text-embedding-3-small",
    memory_blocks=[
        {"label": "persona", "value": "I am a helpful assistant."}
    ]
)

Why Legacy Architectures Exist

Letta evolved from the MemGPT research project. Early versions used specific agent architectures with names like:

• memgpt_agent - Original MemGPT paper implementation
• memgpt_v2_agent - Iteration with sleep-time compute and file tools
• letta_v1_agent - First transition away from MemGPT naming

These names are confusing because:

1. The naming progression (memgpt → memgpt_v2 → letta_v1) is non-standard
2. LLMs trained on these docs get confused about which to recommend
3. New users shouldn’t need to think about architecture choices

Do I Need to Migrate?

If you created your agents recently (after October 2024): You’re likely already on the current architecture. No action needed.

If you have existing agents with agent_type specified: Your agents will continue to work, but we recommend migrating to benefit from:

• Better performance on new models
• Native reasoning support
• Simplified prompting

See our migration guide →

Legacy Architecture Types

If you’re working with older agents or need to understand the differences:

Legacy Type	Status	Key Features	When Used
memgpt_agent	Deprecated	send_message tool, heartbeats, prompted reasoning	MemGPT paper implementation (2023)
memgpt_v2_agent	Deprecated	Sleep-time agents, file tools, unified recall	Iteration with new research (2024)
letta_v1_agent	Legacy	Native reasoning, no send_message, no heartbeats	Transition architecture (early 2025)

Learn more about each legacy type →

Getting Help

• Discord confusion? Share your agent setup in #dev-help
• Need to migrate? Follow our migration guide
• Building something new? Start with our quickstart (no architecture choice needed!)