lagent vs pydantic-ai-harness
Python frameworks for building capable LLM agents
lagent provides a PyTorch-inspired framework for composing agents and message-based workflows, while pydantic-ai-harness adds capabilities to agents built with Pydantic AI. Their focus differs: lagent centers on agent composition and synchronous or asynchronous execution, while the harness offers tools and runtime support for complex, long-running tasks. The harness repository is archived, with development moved to the Pydantic AI repository.
lagent: Build LLM Agents with a PyTorch-Inspired Framework
InternLM’s Lagent is a lightweight Python framework for building LLM-based agents, using a PyTorch-inspired design for composing agents and message passing. It supports synchronous and asynchronous workflows, tools, memory, and multi-agent applications.
pydantic-ai-harness: Add Capabilities to Pydantic AI Agents
Pydantic AI Harness is a Python capability library built on Pydantic AI for giving agents workspaces, memory, delegation, and other tools for complex, long-running tasks. This GitHub repository is archived; development and documentation have moved to the Pydantic AI repository.
| lagent | pydantic-ai-harness | |
|---|---|---|
| Language | Python | Python |
| License | Apache-2.0 | MIT |
| Stars | 2.3k | 958 |
| Forks | 248 | 150 |
| Last analyzed | Oct 15, 2026 | Oct 19, 2026 |
Key differences
- lagent is a standalone agent framework; pydantic-ai-harness is a capability library built on Pydantic AI.
- lagent emphasizes message passing, memory, response parsing, tool execution, and synchronous or asynchronous components; pydantic-ai-harness emphasizes workspaces, planning, delegation, and long-running task support.
- lagent describes multi-agent workflows such as writer-and-critic loops; pydantic-ai-harness offers ready-made Coder and Researcher harnesses and capabilities that can be combined individually.
- lagent is licensed under Apache-2.0, while pydantic-ai-harness is licensed under MIT.
- The lagent repository is not archived and is described as quiet; the pydantic-ai-harness repository is archived and read-only, with current development and documentation in the Pydantic AI repository.
- pydantic-ai-harness requires Python 3.10 or newer and uses 0.x versioning, with a warning that APIs may change between minor releases.
Choose lagent if you…
- need a Python framework for composing message-based agents and multi-agent workflows.
- want synchronous and asynchronous components for agent, model, and tool execution.
- prefer an Apache-2.0 project that is not archived.
Choose pydantic-ai-harness if you…
- build agents on Pydantic AI and want capabilities such as file operations, shell access, or delegation.
- need options for long-running tasks, including persistent runs, context management, and cross-session memory.
- want ready-made Coder or Researcher harnesses, and can follow development in the Pydantic AI repository.
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This comparison is generated with AI from the OSRepos analyses of both projects. Always check each project's repository and documentation before choosing.