dspy-finetune-bootstrap

DSPy BootstrapFinetune Optimizer

Goal

Distill a DSPy program into fine-tuned model weights for efficient production deployment.

When to Use

• You have a working DSPy program with a large model
• Need to reduce inference costs
• Want faster responses (smaller model)
• Deploying to resource-constrained environments

Inputs

| Input | Type | Description | |-------|------|-------------| | program | dspy.Module | Teacher program to distill | | trainset | list[dspy.Example] | Training examples | | metric | callable | Validation metric (optional) | | train_kwargs | dict | Training hyperparameters |

Outputs

| Output | Type | Description | |--------|------|-------------| | finetuned_program | dspy.Module | Program with fine-tuned weights | | model_path | str | Path to saved model |

Workflow

Phase 1: Prepare Teacher Program

import dspy

# Configure with strong teacher model
dspy.configure(lm=dspy.LM("openai/gpt-4o"))

class TeacherQA(dspy.Module):
    def __init__(self):
        self.cot = dspy.ChainOfThought("question -> answer")
    
    def forward(self, question):
        return self.cot(question=question)

Phase 2: Configure Fine-Tuning

Assign the LM directly to predictors before fine-tuning:

import dspy
from dspy.teleprompt import BootstrapFinetune

optimizer = BootstrapFinetune(
    metric=lambda gold, pred, trace=None: gold.answer.lower() in pred.answer.lower(),
    train_kwargs={
        'learning_rate': 5e-5,
        'num_train_epochs': 3,
        'per_device_train_batch_size': 4,
        'warmup_ratio': 0.1
    }
)

Phase 3: Fine-tune Student Model

teacher = TeacherQA()
teacher.set_lm(dspy.settings.lm)
finetuned = optimizer.compile(teacher, trainset=trainset)

Phase 4: Deploy

# Save the fine-tuned model (saves state-only by default)
finetuned.save("finetuned_qa_model.json")

# Load and use (must recreate architecture first)
loaded = TeacherQA()
loaded.load("finetuned_qa_model.json")
result = loaded(question="What is machine learning?")

Production Example

import dspy
from dspy.teleprompt import BootstrapFinetune
from dspy.evaluate import Evaluate
import logging
import os

logger = logging.getLogger(__name__)

class ClassificationSignature(dspy.Signature):
    """Classify text into categories."""
    text: str = dspy.InputField()
    label: str = dspy.OutputField(desc="Category: positive, negative, neutral")

class TextClassifier(dspy.Module):
    def __init__(self):
        self.classify = dspy.Predict(ClassificationSignature)
    
    def forward(self, text):
        return self.classify(text=text)

def classification_metric(gold, pred, trace=None):
    """Exact label match."""
    gold_label = gold.label.lower().strip()
    pred_label = pred.label.lower().strip() if pred.label else ""
    return gold_label == pred_label

def finetune_classifier(trainset, devset, output_dir="./finetuned_model"):
    """Full fine-tuning pipeline."""
    
    # Configure teacher (strong model)
    dspy.configure(lm=dspy.LM("openai/gpt-4o"))
    
    teacher = TextClassifier()
    teacher.set_lm(dspy.settings.lm)
    
    # Evaluate teacher
    evaluator = Evaluate(devset=devset, metric=classification_metric, num_threads=8)
    teacher_score = evaluator(teacher)
    logger.info(f"Teacher score: {teacher_score:.2%}")

    # Fine-tune (train_kwargs passed to constructor)
    optimizer = BootstrapFinetune(
        metric=classification_metric,
        train_kwargs={
            'learning_rate': 2e-5,
            'num_train_epochs': 3,
            'per_device_train_batch_size': 8,
            'gradient_accumulation_steps': 2,
            'warmup_ratio': 0.1,
            'weight_decay': 0.01,
            'logging_steps': 10,
            'save_strategy': 'epoch',
            'output_dir': output_dir
        }
    )

    finetuned = optimizer.compile(
        teacher,
        trainset=trainset
    )
    
    # Evaluate fine-tuned model
    student_score = evaluator(finetuned)
    logger.info(f"Student score: {student_score:.2%}")

    # Save (state-only as JSON)
    finetuned.save(os.path.join(output_dir, "final_model.json"))

    return {
        "teacher_score": teacher_score,
        "student_score": student_score,
        "model_path": os.path.join(output_dir, "final_model.json")
    }

# For RAG fine-tuning
class RAGClassifier(dspy.Module):
    """RAG pipeline that can be fine-tuned."""
    
    def __init__(self, num_passages=3):
        self.retrieve = dspy.Retrieve(k=num_passages)
        self.classify = dspy.ChainOfThought("context, text -> label")
    
    def forward(self, text):
        context = self.retrieve(text).passages
        return self.classify(context=context, text=text)

def finetune_rag_classifier(trainset, devset):
    """Fine-tune a RAG-based classifier."""

    # Configure retriever and LM
    colbert = dspy.ColBERTv2(url='http://20.102.90.50:2017/wiki17_abstracts')
    dspy.configure(
        lm=dspy.LM("openai/gpt-4o"),
        rm=colbert
    )

    rag = RAGClassifier()
    rag.set_lm(dspy.settings.lm)

    # Fine-tune (train_kwargs in constructor)
    optimizer = BootstrapFinetune(
        metric=classification_metric,
        train_kwargs={
            'learning_rate': 1e-5,
            'num_train_epochs': 5
        }
    )

    finetuned = optimizer.compile(
        rag,
        trainset=trainset
    )

    return finetuned

Training Arguments Reference

| Argument | Description | Typical Value | |----------|-------------|---------------| | learning_rate | Learning rate | 1e-5 to 5e-5 | | num_train_epochs | Training epochs | 3-5 | | per_device_train_batch_size | Batch size | 4-16 | | gradient_accumulation_steps | Gradient accumulation | 2-8 | | warmup_ratio | Warmup proportion | 0.1 | | weight_decay | L2 regularization | 0.01 | | max_grad_norm | Gradient clipping | 1.0 |

Best Practices

1. Strong teacher - Use GPT-4 or Claude as teacher
2. Quality data - Teacher traces are only as good as training examples
3. Validate improvement - Compare student to teacher on held-out set
4. Start with more epochs - Fine-tuning often needs 3-5 epochs
5. Monitor overfitting - Track validation loss during training

Limitations

• Requires a provider and model that support fine-tuning
• Training requires GPU resources
• Student may not match teacher quality on all inputs
• Fine-tuning takes hours/days depending on data size
• Model size reduction may cause capability loss

Official Documentation

• DSPy Documentation: https://dspy.ai/
• DSPy GitHub: https://github.com/stanfordnlp/dspy
• BootstrapFinetune API: https://dspy.ai/api/optimizers/BootstrapFinetune/
• Fine-tuning Guide: https://dspy.ai/tutorials/classification_finetuning/