Agent Lightning
Microsoft's lightweight trainer that improves existing agents with reinforcement learning through a model proxy, without rewriting the agent's tools or control flow.
Updated
✨ Try AgentScout's free AI image generator →Good for: building AI agents, training and fine-tuning agents
Use cases
About Agent Lightning
Agent Lightning is listed in our frameworks category and is aimed at builders. Microsoft's lightweight trainer that improves existing agents with reinforcement learning through a model proxy, without rewriting the agent's tools or control flow. Pricing, as the maker states it: Open source. Maturity: Mature. We last checked the official link on 2026-10-17.
What is Agent Lightning?
Agent Lightning is Microsoft's lightweight framework (about 3,500 lines) for training existing agents with reinforcement learning using their real harnesses, without rewriting the agent's tools or control flow. It is MIT-licensed and was refactored in v1.0.
Its README reports a 2026 example where pure RL improved Qwen3.5-35B-A3B on SWE-bench Verified from 47.8% to 61.6% with 1.8K training examples, and an Agent Lightning Skill that helps one coding agent improve another.
Sources: the official README and our directory listing, checked 2026-10-18. Official site: microsoft.github.io/agent-lightning.
Who is Agent Lightning for?
ML engineers and researchers who want to improve an existing agent with RL instead of rebuilding it.
Agent Lightning at a glance
- Open source: Yes (MIT License)
- GitHub: microsoft/agent-lightning · 18,779 stars (as of Oct 21, 2026)
Key features
- RL training with your agent's real harness
- No rewrite of tools or control flow
- About 3,500 lines; MIT license
- Published coding-agent results
Agent Lightning FAQ
What is Agent Lightning?
Agent Lightning is Microsoft's lightweight framework (about 3,500 lines) for training existing agents with reinforcement learning using their real harnesses, without rewriting the agent's tools or control flow. It is MIT-licensed and was refactored in v1.0.
Who is Agent Lightning for?
ML engineers and researchers who want to improve an existing agent with RL instead of rebuilding it.
Is Agent Lightning free?
Agent Lightning's pricing, as the maker states it: Open source. Open-source tools are free to use, though you may still pay for model API usage or a hosted plan. Check the official site for current plans.
Is Agent Lightning open source?
Yes. Agent Lightning is released under the MIT License, according to its GitHub repository.
What are alternatives to Agent Lightning?
Similar tools include OpenPipe, AReaL, RAGEN, Mirascope, Lagent and AWorld.
Agent Lightning ratings and reviews
Be the first to rate Agent Lightning: tap 1 to 5 stars below. A written review is optional.
Agent Lightning alternatives
Other frameworks tools in our directory. See all frameworks tools →
OpenPipe
Reinforcement learning tooling, including the ART library, to train better agents.
AReaL
Reinforcement learning system for training LLM-based agents.
RAGEN
Reinforcement learning framework for multi-turn LLM agents.
Mirascope
Lightweight Python library for calling any LLM with typed outputs and tools through one interface, without a heavy framework.
Lagent
Lightweight PyTorch-inspired framework from InternLM for building LLM-based agents.
AWorld
Agent harness from inclusionAI for building expert agents that search, reproduce and improve on ideas with their own tools and memory.
Related lists
🏆 See also: AutoGen alternatives · All best-of lists
🧭 Task guides: Training and fine-tuning tools for building AI agents
💲 Estimate API cost: compare per-request and monthly costs for GPT, Claude, Gemini and Grok models.
Badge for makers
Built Agent Lightning? Add this badge to your README or site. It links back to this page. About badges
