Build a Multi-Step AI Pipeline

Guide the user through breaking a complex AI task into multiple steps that feed into each other. One prompt can't do everything — compound AI systems dramatically outperform single calls by decomposing problems.

Step 1: Understand the pipeline

Ask the user:

1. What's the end-to-end task? (e.g., "read a support ticket, classify it, draft a response")
2. What are the natural stages? (classification, retrieval, generation, verification?)
3. Does any step need special tools? (search, database, calculator?)
4. Does data flow linearly, or do steps branch/loop?

Step 2: Design the stages

The core pattern — compose DSPy modules

Every stage is a DSPy module. Wire them together in forward():

import dspy

class SupportPipeline(dspy.Module):
    def __init__(self):
        self.classify = dspy.ChainOfThought(ClassifyTicket)
        self.retrieve = dspy.Retrieve(k=3)
        self.draft = dspy.ChainOfThought(DraftResponse)

    def forward(self, ticket):
        # Stage 1: Classify
        classification = self.classify(ticket=ticket)

        # Stage 2: Retrieve relevant docs
        docs = self.retrieve(classification.category + " " + ticket).passages

        # Stage 3: Draft response using classification + docs
        return self.draft(
            ticket=ticket,
            category=classification.category,
            context=docs,
        )

Each stage has its own signature:

from typing import Literal

CATEGORIES = ["billing", "technical", "account", "general"]

class ClassifyTicket(dspy.Signature):
    """Classify the support ticket."""
    ticket: str = dspy.InputField()
    category: Literal[tuple(CATEGORIES)] = dspy.OutputField()

class DraftResponse(dspy.Signature):
    """Draft a helpful response to the support ticket."""
    ticket: str = dspy.InputField()
    category: str = dspy.InputField()
    context: list[str] = dspy.InputField(desc="Relevant help articles")
    response: str = dspy.OutputField(desc="Professional support response")

Step 3: Common pipeline patterns

Classify → Route → Specialize

Different categories get different handling:

class RoutedPipeline(dspy.Module):
    def __init__(self):
        self.classify = dspy.ChainOfThought(ClassifyInput)
        self.handlers = {
            "simple": dspy.Predict(SimpleAnswer),
            "complex": dspy.ChainOfThought(DetailedAnswer),
            "research": dspy.ChainOfThought(ResearchAnswer),
        }

    def forward(self, question):
        category = self.classify(question=question).category
        handler = self.handlers.get(category, self.handlers["simple"])
        return handler(question=question)

Generate → Verify → Refine

Generate a first draft, check it, then improve:

class GenerateAndRefine(dspy.Module):
    def __init__(self):
        self.generate = dspy.ChainOfThought(GenerateDraft)
        self.verify = dspy.ChainOfThought(CheckQuality)
        self.refine = dspy.ChainOfThought(ImproveDraft)

    def forward(self, task):
        # Stage 1: Generate
        draft = self.generate(task=task)

        # Stage 2: Verify
        check = self.verify(task=task, draft=draft.output)

        # Stage 3: Refine if needed
        if not check.is_good:
            refined = self.refine(
                task=task,
                draft=draft.output,
                feedback=check.feedback,
            )
            return refined

        return draft

Ensemble — ask multiple times, pick the best

Generate several candidates and select the best one (the pattern behind AlphaCode and Medprompt):

class EnsemblePipeline(dspy.Module):
    def __init__(self, num_candidates=5):
        self.generators = [dspy.ChainOfThought(GenerateAnswer) for _ in range(num_candidates)]
        self.judge = dspy.ChainOfThought(PickBestAnswer)

    def forward(self, question):
        # Stage 1: Generate multiple candidates
        candidates = []
        for gen in self.generators:
            result = gen(question=question)
            candidates.append(result.answer)

        # Stage 2: Pick the best
        return self.judge(
            question=question,
            candidates=candidates,
        )

class PickBestAnswer(dspy.Signature):
    """Pick the best answer from the candidates."""
    question: str = dspy.InputField()
    candidates: list[str] = dspy.InputField(desc="Multiple answer candidates")
    best_answer: str = dspy.OutputField(desc="The most accurate and complete answer")
    reasoning: str = dspy.OutputField(desc="Why this answer was chosen")

Parallel fan-out → merge

Process different aspects independently, then combine:

class ParallelAnalysis(dspy.Module):
    def __init__(self):
        self.sentiment = dspy.ChainOfThought(AnalyzeSentiment)
        self.topics = dspy.ChainOfThought(ExtractTopics)
        self.entities = dspy.ChainOfThought(ExtractEntities)
        self.summarize = dspy.ChainOfThought(CombineAnalysis)

    def forward(self, text):
        # Fan out — run in parallel (DSPy can parallelize these)
        sent = self.sentiment(text=text)
        topics = self.topics(text=text)
        entities = self.entities(text=text)

        # Merge results
        return self.summarize(
            text=text,
            sentiment=sent.sentiment,
            topics=topics.topics,
            entities=entities.entities,
        )

Loop — iterative refinement

Keep improving until a condition is met:

class IterativeRefiner(dspy.Module):
    def __init__(self, max_iterations=3):
        self.generate = dspy.ChainOfThought(GenerateDraft)
        self.evaluate = dspy.ChainOfThought(EvaluateDraft)
        self.improve = dspy.ChainOfThought(ImproveDraft)
        self.max_iterations = max_iterations

    def forward(self, task):
        draft = self.generate(task=task)

        for i in range(self.max_iterations):
            evaluation = self.evaluate(task=task, draft=draft.output)
            if evaluation.score >= 0.9:
                break
            draft = self.improve(
                task=task,
                draft=draft.output,
                feedback=evaluation.feedback,
            )

        return draft

Step 4: Use different models per stage

Not every stage needs the same model. Use cheap models for simple steps:

expensive_lm = dspy.LM("openai/gpt-4o")
cheap_lm = dspy.LM("openai/gpt-4o-mini")

pipeline = SupportPipeline()

# Cheap model for classification (simple task)
pipeline.classify.lm = cheap_lm

# Expensive model for drafting (needs quality)
pipeline.draft.lm = expensive_lm

See /ai-cutting-costs for more cost optimization strategies.

Step 5: Test and optimize the full pipeline

The beauty of DSPy pipelines: you optimize the whole thing end-to-end, not each step separately.

def pipeline_metric(example, prediction, trace=None):
    # Score the final output quality
    return prediction.response.lower().strip() == example.response.lower().strip()

# Optimizes prompts for ALL stages together
optimizer = dspy.MIPROv2(metric=pipeline_metric, auto="medium")
optimized = optimizer.compile(pipeline, trainset=trainset)

Key patterns

• Decompose the problem — if a task has distinct phases (understand, retrieve, generate, verify), make each one a module
• Each stage gets its own signature — clear inputs and outputs make the pipeline debuggable
• Wire in forward() — the forward method is your orchestration logic
• Optimize end-to-end — DSPy optimizers tune all stages together to maximize the final metric
• Debug stage by stage — use dspy.inspect_history() to see what each step did
• Assign models per stage — cheap models for simple tasks, expensive for complex ones

When to use LangGraph instead

DSPy pipelines are great for stateless, linear-ish flows. But some problems need more:

Quick example: DSPy module as a LangGraph node

import dspy
from langgraph.graph import StateGraph, START, END
from typing import TypedDict

class PipelineState(TypedDict):
    input_text: str
    category: str
    output: str

# DSPy modules
classifier = dspy.ChainOfThought("text -> category")
generator = dspy.ChainOfThought("text, category -> output")

# Wrap as LangGraph nodes
def classify_node(state: PipelineState) -> dict:
    result = classifier(text=state["input_text"])
    return {"category": result.category}

def generate_node(state: PipelineState) -> dict:
    result = generator(text=state["input_text"], category=state["category"])
    return {"output": result.output}

# Build graph
graph = StateGraph(PipelineState)
graph.add_node("classify", classify_node)
graph.add_node("generate", generate_node)
graph.add_edge(START, "classify")
graph.add_edge("classify", "generate")
graph.add_edge("generate", END)
app = graph.compile()

This gives you LangGraph's state management and routing with DSPy's optimizable prompts. For more, see /ai-building-chatbots (stateful conversations) and /ai-coordinating-agents (multi-agent systems). For the full LangGraph API reference, see docs/langchain-langgraph-reference.md.

Additional resources

• Use /ai-checking-outputs to add verification and guardrails between stages
• Use /ai-cutting-costs to assign different models per stage
• Not sure what stages your pipeline needs? Use /ai-decomposing-tasks to identify where to split
• For content generation pipelines, see /ai-writing-content. For complex reasoning, see /ai-reasoning
• Next: /ai-improving-accuracy to measure and improve your pipeline