v0.12.1

Major Features

New Agent Architecture: letta_v1_agent

The new recommended agent architecture with significant improvements over the legacy agent system.
What's Different:

• No send_message tool required
• Works with any chat model, including non-tool-calling models
• No heartbeat system
• Simpler base system prompt - agentic control loop understanding is baked into modern LLMs
• Follows standard tool calling patterns (auto mode) for broader compatibility

Provider Support:

• Compatible with all inference providers (OpenRouter, Azure, Together, Ollama, etc.).
• Works with non-tool-calling models.
• Supports OpenAI's Responses API for drastically improved performance with GPT-5 models.

Trade-offs:

• No heartbeats: Agents won't independently trigger repeated execution. If you need sleep-time compute or periodic processing, implement this through your own prompting or scheduling.
• Tool rules on messaging: Cannot apply tool rules to agent messaging, i.e. you cannot require a particular tool to be followed by an assistant message.
• Reasoning visibility: Non-reasoning models (GPT-4.1, GPT-4o-mini) will no longer generate explicit reasoning output.
• Reasoning control: Less control over reasoning tokens, which are typically encrypted by providers and cannot be passed between different providers.

Recommendation: Create all new agents as letta_v1_agent. The expanded provider compatibility and simpler architecture make this the best choice for most use cases. Use legacy agents only if you specifically need heartbeats or tool rules on messaging.

Human-in-the-Loop (HITL)

Tools can now require human approval before execution. Set approval requirements via API or in the ADE for greater control over agent actions.
📖 Documentation

Parallel Tool Calling

Agents now execute multiple tool calls simultaneously when supported by the inference provider. Each tool runs in its own sandbox for true parallel execution. See the Claude documentation for examples on parallel tool calling.

Runs API

New tracking system providing substantially improved observability and debugging capabilities. Documentation coming soon.

Enhanced Archival Memory (Letta Cloud only)

• Hybrid search: Combines full-text and semantic search
• DateTime filtering: Query memories by time range
• Search API endpoint: Documentation

Improved Pagination

Cursor-based pagination now available across many endpoints for handling large result sets.

New Tools

Memory Omni-Tool

Unified memory interface for more intuitive agent memory management.

📖 Blog post | YouTube demo

fetch_webpage Tool

Utility tool for retrieving LLM-friendly webpage content.

Agent Configuration

Templates & Agentfiles

• Template updates: Templates can now be updated via agentfiles
• Agentfile v2 schema: Now supports groups, folders, etc.

Breaking Changes

Deprecated APIs

• get_folder_by_name: Use client.folders.list(name=...) instead
• sources routes: All routes renamed to folders

What's Changed

• fix: summarization_agent unknown attribute bug by @carenthomas in #3028
• fix: open router invalid model id bug by @carenthomas in #3028
• chore: bump version 0.12.1 by @carenthomas in #3029

Full Changelog: 0.12.0...0.12.1