Agent Lightning

Microsoft's framework for training AI agents with reinforcement learning, automatic prompt optimization, and supervised fine-tuning.

Quick Start

Installation

pip install agentlightning

For nightly builds:

pip install --upgrade --index-url https://test.pypi.org/simple/ --extra-index-url https://pypi.org/simple/ --pre agentlightning

Minimal Integration (Zero Code Change)

Add agl.emit_xxx() helpers to your existing agent:

import agentlightning as agl

# Your existing agent code
def my_agent(task):
    agl.emit_input(task)  # Track input

    response = llm.generate(task)
    agl.emit_output(response)  # Track output

    reward = evaluate(response)
    agl.emit_reward(reward)  # Track reward

    return response

Core Concepts

Architecture Flow

Agent (your code) → agl.emit_xxx() → Spans → LightningStore → Algorithm → Updated Resources

Key Components

Component	Purpose
LightningStore	Central hub for traces, tasks, and resources
Tracer	Collects spans from agent execution
Algorithm	Consumes traces, produces improvements
Trainer	Orchestrates training loop

Instrumentation

Emit Functions

import agentlightning as agl

# Basic emissions
agl.emit_input(prompt)           # Track input to agent
agl.emit_output(response)        # Track agent output
agl.emit_reward(score)           # Track reward signal
agl.emit_tool_call(name, args)   # Track tool usage
agl.emit_tool_result(result)     # Track tool results

Tracer Context

from agentlightning import Tracer

tracer = Tracer(store=store)

with tracer.trace_context(task_id="task-123"):
    # All emissions within this context are grouped
    result = agent.run(task)

# Retrieve trace after execution
trace = tracer.get_last_trace()

OpenTelemetry Integration

Agent Lightning integrates with OpenTelemetry:

from agentlightning.utils.otel import get_tracer

tracer = get_tracer()  # Returns OTel tracer for "agentlightning"

LightningStore

In-Memory Store (Development)

from agentlightning.store.memory import InMemoryLightningStore

store = InMemoryLightningStore()

Client-Server Store (Production)

from agentlightning.store.client_server import (
    LightningStoreServer,
    LightningStoreClient
)

# Server side
server = LightningStoreServer(store, host="0.0.0.0", port=8080)
await server.start()

# Client side
client = LightningStoreClient("http://localhost:8080")

Store Operations

# Add rollouts (tasks for the agent)
await store.enqueue_rollout(task=task, config=RolloutConfig())

# Query rollouts
rollouts = await store.query_rollouts(status_in=["completed"])

# Add resources (updated prompts, weights)
await store.add_resources(resources)

# Get latest resources
resources = await store.get_latest_resources()

Training

Basic Trainer Setup

import agentlightning as agl

trainer = agl.Trainer(
    n_runners=8,           # Parallel rollout workers
    algorithm=algorithm,   # Your chosen algorithm
    store=store           # Optional, creates InMemory if not provided
)

trainer.run()

Custom Algorithm

from agentlightning import LightningStore
from agentlightning.types import ExecutionEvent

async def my_algorithm(store: LightningStore, event: ExecutionEvent):
    # Fetch completed rollouts
    rollouts = await store.query_rollouts(status_in=["completed"])

    # Process traces, compute gradients, etc.
    new_resources = optimize(rollouts)

    # Push updated resources
    await store.add_resources(new_resources)

Runner Function

async def my_runner(store: LightningStore, worker_id: int, event: ExecutionEvent):
    while not event.is_set():
        rollout = await store.dequeue_rollout()
        if rollout:
            result = execute_task(rollout.task)
            await store.update_rollout(
                rollout_id=rollout.id,
                status="completed",
                result=result
            )

Algorithms

Reinforcement Learning (GRPO/PPO)

For RL training with vLLM backend:

from agentlightning.algorithm.verl import VeRLAlgorithm

algorithm = VeRLAlgorithm(
    model="your-model",
    learning_rate=1e-5,
    batch_size=32
)

Automatic Prompt Optimization (APO)

from agentlightning.algorithm.apo import APOAlgorithm

algorithm = APOAlgorithm(
    optimizer_model="gpt-4",
    target_model="gpt-3.5-turbo"
)

Framework Adapters

LangChain

from agentlightning.instrumentation.langchain import instrument_langchain

instrument_langchain()  # Auto-traces all LangChain calls

OpenAI SDK

from agentlightning.instrumentation.openai import instrument_openai

instrument_openai()  # Auto-traces OpenAI API calls

vLLM

from agentlightning.instrumentation.vllm import instrument_vllm

instrument_vllm()  # Instrument vLLM for token-level tracing

Logging & Debugging

Configure Logging

from agentlightning import setup_logging

setup_logging(
    level="DEBUG",
    submodule_levels={
        "agentlightning.store": "INFO",
        "agentlightning.tracer": "DEBUG"
    }
)

Metrics

Agent Lightning emits Prometheus-compatible metrics:

• agl.store.total - Store operation counts
• agl.store.latency - Store operation latencies
• agl.rollouts.total - Rollout counts by status
• agl.rollouts.duration - Rollout execution times

Common Patterns

Reward Function Design

def compute_reward(task, response):
    """Good rewards are: normalized, dense when possible, aligned with goals."""

    correctness = check_correctness(task, response)  # 0-1
    efficiency = measure_efficiency(response)         # 0-1

    return 0.7 * correctness + 0.3 * efficiency

Multi-Agent Training

Train specific agents in a multi-agent system:

with tracer.trace_context(agent_id="planner"):
    plan = planner.run(task)

with tracer.trace_context(agent_id="executor"):
    result = executor.run(plan)

# Only the executor's traces are used for training

Checkpoint & Resume

# Save checkpoint
await store.add_resources(
    checkpoint=True,
    resources=current_resources
)

# Load latest
resources = await store.get_latest_resources()

Integration with JavaScript Agents

For JavaScript/TypeScript agents (like Claude-based apps), you have two options:

Option 1: Python Training Service

Create a Python microservice that:

1. Receives trace events from your JS app via HTTP
2. Stores them in LightningStore
3. Runs training algorithms
4. Returns optimized prompts

Option 2: REST API Integration

Use LightningStoreServer as a REST backend:

// JavaScript client
const response = await fetch('http://localhost:8080/rollouts', {
    method: 'POST',
    body: JSON.stringify({
        task: { prompt: userMessage },
        config: { max_retries: 3 }
    })
});

Resources

• Documentation
• GitHub
• arXiv Paper
• Discord Community

Troubleshooting

Issue	Solution
Import errors	Ensure pip install agentlightning succeeded
Store connection failed	Check server is running, verify endpoint URL
No traces collected	Verify emit_xxx() calls are within trace context
Training not converging	Check reward function normalization, increase rollouts