LangChain Integration Guide

LangChain Integration Guide

This guide shows how to use cascadeflow with LangChain for intelligent AI model cascading with 40-85% cost savings while maintaining full LangChain compatibility.

Table of Contents

1. Overview
2. Installation
3. Quick Start
4. Configuration
5. Key Features
6. Use Cases
7. Best Practices
8. Troubleshooting

Overview

The @cascadeflow/langchain package brings cascadeflow's intelligent model cascading to LangChain applications as a drop-in replacement for standard LangChain chat models.

What is Model Cascading?

Instead of always using expensive models:

Traditional: Every query → GPT-4o ($0.0025)

cascadeflow tries cheap models first:

cascadeflow:
  1. Try GPT-4o-mini ($0.00015) ← 70-80% stop here! ✅
  2. Validate quality automatically
  3. If needed → GPT-4o ($0.0025)

Result: 50-85% cost savings

How It Works with LangChain

cascadeflow wraps any LangChain chat model and provides intelligent routing:

Architecture:

┌─────────────────────────────────────────┐
│         Your LangChain Application       │
│                                          │
│  ┌────────────────────────────────────┐ │
│  │      withCascade (Proxy)        │ │
│  ├────────────────────────────────────┤ │
│  │  1. Route to Drafter (GPT-4o-mini) │ │
│  │  2. Quality Check (90% pass!)      │ │
│  │  3. Escalate to Verifier if needed │ │
│  └────────────────────────────────────┘ │
│                                          │
│  Supports: LCEL, Streaming, Tools, Batch │
└─────────────────────────────────────────┘

Key Benefits:

• 🎯 Drop-in Replacement: Works with all LangChain features
• 💰 Cost Savings: 40-85% reduction in API costs
• ⚡ Speed: Faster responses (drafter is quicker)
• 🔧 Zero Config: Works out of the box with sensible defaults
• 📊 LangSmith Integration: Automatic cost tracking metadata

Installation

npm install @cascadeflow/langchain @langchain/core @langchain/openai

Or with yarn:

yarn add @cascadeflow/langchain @langchain/core @langchain/openai

Quick Start

Basic Usage

import { ChatOpenAI } from '@langchain/openai';
import { withCascade } from '@cascadeflow/langchain';

// Create your models
const drafter = new ChatOpenAI({
  modelName: 'gpt-4o-mini',
  temperature: 0.7
});

const verifier = new ChatOpenAI({
  modelName: 'gpt-4o',
  temperature: 0.7
});

// Wrap them with cascade
const cascade = withCascade({
  drafter,
  verifier,
  qualityThreshold: 0.8, // 80% of queries will use drafter
});

// Use it like any LangChain chat model
const response = await cascade.invoke('Explain quantum computing');
console.log(response.content);

With LCEL (LangChain Expression Language)

import { PromptTemplate } from '@langchain/core/prompts';
import { StringOutputParser } from '@langchain/core/output_parsers';

const prompt = PromptTemplate.fromTemplate(
  'You are a helpful assistant. Answer: {question}'
);

// Chain with cascade using pipe
const chain = prompt
  .pipe(cascade)
  .pipe(new StringOutputParser());

const result = await chain.invoke({
  question: 'What is machine learning?'
});

Configuration

withCascade Options

interface CascadeConfig {
  // Required: The fast, cheap model
  drafter: BaseChatModel;

  // Required: The high-quality model (fallback)
  verifier: BaseChatModel;

  // Quality threshold (0-1)
  // Higher = more queries use drafter
  // Default: 0.8
  qualityThreshold?: number;

  // Custom quality check function
  qualityCheck?: (response: BaseMessage) => Promise<number>;

  // Enable debug logging
  verbose?: boolean;
}

Quality Threshold Guide

Model Combinations

OpenAI:

const drafter = new ChatOpenAI({ modelName: 'gpt-4o-mini' });
const verifier = new ChatOpenAI({ modelName: 'gpt-4o' });

Anthropic:

import { ChatAnthropic } from '@langchain/anthropic';

const drafter = new ChatAnthropic({ modelName: 'claude-3-haiku-20240307' });
const verifier = new ChatAnthropic({ modelName: 'claude-3-5-sonnet-20241022' });

Mix and Match:

// Cheap drafter (Haiku), powerful verifier (GPT-4o)
const drafter = new ChatAnthropic({ modelName: 'claude-3-haiku-20240307' });
const verifier = new ChatOpenAI({ modelName: 'gpt-4o' });

Key Features

1. Streaming Support

Full streaming support with automatic pre-routing:

// Stream from cascade
const stream = await cascade.stream('Write a story about a robot');

for await (const chunk of stream) {
  process.stdout.write(chunk.content);
}

How it works:

• Pre-routing: Cascade decides drafter vs verifier BEFORE streaming
• No latency: Stream starts immediately
• Consistent: Full response from one model

2. Tool Calling & Function Calling

Bind tools to cascade - they propagate to both models:

const tools = [
  {
    name: 'calculator',
    description: 'Performs arithmetic operations',
    parameters: {
      type: 'object',
      properties: {
        operation: {
          type: 'string',
          enum: ['add', 'subtract', 'multiply', 'divide']
        },
        a: { type: 'number' },
        b: { type: 'number' },
      },
      required: ['operation', 'a', 'b'],
    },
  },
];

// Bind tools to cascade
const boundCascade = cascade.bindTools(tools);

const result = await boundCascade.invoke(
  'What is 15 plus 27?'
);

// Result includes tool calls
console.log(result.tool_calls);

3. Structured Output

Extract structured data with schemas:

const userSchema = {
  type: 'object',
  properties: {
    name: { type: 'string' },
    age: { type: 'number' },
    email: { type: 'string' },
  },
  required: ['name', 'age'],
};

const structuredCascade = cascade.withStructuredOutput(userSchema);

const result = await structuredCascade.invoke(
  'Extract info: John Smith is 28 years old. Email: john@example.com'
);

// { name: 'John Smith', age: 28, email: 'john@example.com' }

4. Batch Processing

Process multiple inputs efficiently:

const questions = [
  'What is 2+2?',
  'What is the speed of light?',
  'Who wrote Romeo and Juliet?',
];

const results = await cascade.batch(questions);

results.forEach((result, i) => {
  console.log(`Q: ${questions[i]}`);
  console.log(`A: ${result.content}\n`);
});

5. LCEL Composition Patterns

Sequential Chains:

import { RunnableSequence } from '@langchain/core/runnables';

const chain = RunnableSequence.from([
  prompt,
  cascade,
  new StringOutputParser(),
]);

Parallel Branches:

import { RunnablePassthrough } from '@langchain/core/runnables';

const chain = RunnablePassthrough.assign({
  answer: cascade.pipe(new StringOutputParser()),
  context: () => 'Generated by cascadeflow',
});

const result = await chain.invoke('What is AI?');
// { answer: '...', context: 'Generated by cascadeflow' }

Complex Patterns:

// Multi-step reasoning
const analysisChain = RunnableSequence.from([
  // Step 1: Analyze
  RunnablePassthrough.assign({
    analysis: cascade.pipe(new StringOutputParser()),
  }),
  // Step 2: Summarize
  (input) => ({
    question: input.question,
    analysis: input.analysis,
    prompt: `Summarize this analysis: ${input.analysis}`,
  }),
  // Step 3: Summary
  RunnablePassthrough.assign({
    summary: cascade.pipe(new StringOutputParser()),
  }),
]);

6. LangSmith Integration

Automatic cost tracking metadata:

// Metadata is automatically injected into responses
const result = await cascade.invoke('test');

// Access via response_metadata
console.log(result.response_metadata.cascade);
/*
{
  route: 'drafter',
  model: 'gpt-4o-mini',
  estimated_cost: 0.00015,
  quality_score: 0.85
}
*/

View in LangSmith traces:

1. Open LangSmith dashboard
2. View trace for your request
3. Check metadata for cost breakdown
4. Track savings over time

Use Cases

1. Customer Support Chatbot

import { ChatOpenAI } from '@langchain/openai';
import { withCascade } from '@cascadeflow/langchain';
import { PromptTemplate } from '@langchain/core/prompts';

const supportPrompt = PromptTemplate.fromTemplate(`
You are a helpful customer support agent.
Previous context: {context}
User question: {question}

Provide a clear, helpful answer.
`);

const cascade = withCascade({
  drafter: new ChatOpenAI({ modelName: 'gpt-4o-mini' }),
  verifier: new ChatOpenAI({ modelName: 'gpt-4o' }),
  qualityThreshold: 0.85, // Most queries use cheap model
});

const chain = supportPrompt.pipe(cascade);

// Simple questions → drafter (cheap)
await chain.invoke({
  context: '',
  question: 'What are your business hours?',
});

// Complex questions → verifier (expensive)
await chain.invoke({
  context: 'User has account issues',
  question: 'How do I recover my account with 2FA enabled?',
});

Savings: 70-80% cost reduction on support queries

2. Document Q&A with RAG

import { ChatOpenAI } from '@langchain/openai';
import { withCascade } from '@cascadeflow/langchain';
import { PromptTemplate } from '@langchain/core/prompts';
import { StringOutputParser } from '@langchain/core/output_parsers';

const ragPrompt = PromptTemplate.fromTemplate(`
Context: {context}

Question: {question}

Answer based on the context above.
`);

const cascade = withCascade({
  drafter: new ChatOpenAI({ modelName: 'gpt-4o-mini' }),
  verifier: new ChatOpenAI({ modelName: 'gpt-4o' }),
  qualityThreshold: 0.8,
});

const chain = ragPrompt
  .pipe(cascade)
  .pipe(new StringOutputParser());

const answer = await chain.invoke({
  context: retrievedDocs,
  question: userQuestion,
});

Savings: 60-75% cost reduction on RAG applications

3. Data Extraction Pipeline

const extractionSchema = {
  type: 'object',
  properties: {
    entities: {
      type: 'array',
      items: {
        type: 'object',
        properties: {
          name: { type: 'string' },
          type: { type: 'string' },
          confidence: { type: 'number' },
        },
      },
    },
  },
};

const cascade = withCascade({
  drafter: new ChatOpenAI({ modelName: 'gpt-4o-mini' }),
  verifier: new ChatOpenAI({ modelName: 'gpt-4o' }),
});

const extractor = cascade.withStructuredOutput(extractionSchema);

// Batch process documents
const documents = [...]; // Your documents
const results = await extractor.batch(
  documents.map(doc => `Extract entities from: ${doc}`)
);

Savings: 50-70% cost reduction on extraction tasks

4. Code Review Assistant

const codeReviewPrompt = PromptTemplate.fromTemplate(`
Review this code for best practices, bugs, and improvements:

{code}

Provide:
1. Issues found (if any)
2. Suggested improvements
3. Overall assessment
`);

const cascade = withCascade({
  drafter: new ChatOpenAI({ modelName: 'gpt-4o-mini' }),
  verifier: new ChatOpenAI({ modelName: 'gpt-4o' }),
  qualityThreshold: 0.75, // More critical task
});

const chain = codeReviewPrompt.pipe(cascade);

const review = await chain.invoke({ code: userCode });

Savings: 60-70% cost reduction on code reviews

Best Practices

1. Choose the Right Quality Threshold

// High-volume, low-stakes
const chatbot = withCascade({
  drafter, verifier,
  qualityThreshold: 0.9, // 90% use drafter
});

// Critical business logic
const criticalAnalysis = withCascade({
  drafter, verifier,
  qualityThreshold: 0.6, // 60% use drafter
});

2. Monitor with LangSmith

import { LangChainTracer } from 'langchain/callbacks';

const tracer = new LangChainTracer({
  projectName: 'my-cascade-project',
});

const result = await cascade.invoke('test', {
  callbacks: [tracer],
});

// View traces in LangSmith dashboard
// Track: route decisions, costs, quality scores

3. Custom Quality Checks

const cascade = withCascade({
  drafter,
  verifier,
  qualityCheck: async (response) => {
    // Custom logic
    const content = response.content.toString();

    // Check length
    if (content.length < 50) return 0.5;

    // Check for specific keywords
    if (content.includes('I don't know')) return 0.3;

    // Check for citations
    if (content.match(/\[\d+\]/)) return 0.9;

    return 0.8; // Default score
  },
});

4. Optimize Model Selection

For Simple Tasks:

// Use smallest models
const drafter = new ChatOpenAI({ modelName: 'gpt-4o-mini' });
const verifier = new ChatOpenAI({ modelName: 'gpt-4o-mini' }); // Same model
// Set high threshold
qualityThreshold: 0.95

For Complex Tasks:

// Use model gap
const drafter = new ChatOpenAI({ modelName: 'gpt-4o-mini' });
const verifier = new ChatOpenAI({ modelName: 'o1-preview' }); // Most powerful
// Set moderate threshold
qualityThreshold: 0.7

5. Streaming Best Practices

// Pre-route for consistent streaming
const stream = await cascade.stream(input, {
  // Optional: Force drafter for known simple queries
  metadata: { force_drafter: true },
});

for await (const chunk of stream) {
  // Handle chunks
  process.stdout.write(chunk.content);
}

Troubleshooting

Issue: Too Many Verifier Calls

Symptom: Higher costs than expected

Solution 1: Increase quality threshold

const cascade = withCascade({
  drafter, verifier,
  qualityThreshold: 0.85, // Increased from 0.8
});

Solution 2: Improve drafter model

// Use better drafter
const drafter = new ChatOpenAI({
  modelName: 'gpt-4o-mini',
  temperature: 0.3, // More deterministic
});

Solution 3: Add custom quality check

qualityCheck: async (response) => {
  // More lenient check
  return 0.9; // Accept most responses
}

Issue: Tools Not Working

Symptom: Tool calls not appearing

Solution: Ensure models support tools

// ✅ Good - models support tools
const drafter = new ChatOpenAI({ modelName: 'gpt-4o-mini' });
const verifier = new ChatOpenAI({ modelName: 'gpt-4o' });

// ❌ Bad - model doesn't support tools
const drafter = new ChatOpenAI({ modelName: 'gpt-3.5-turbo' });

Issue: Streaming Not Working

Symptom: No chunks received

Solution: Check model streaming support

// Ensure both models support streaming
const drafter = new ChatOpenAI({
  modelName: 'gpt-4o-mini',
  streaming: true, // Enable streaming
});

Issue: Type Errors with LCEL

Symptom: TypeScript errors in chains

Solution: Use explicit types

import type { Runnable } from '@langchain/core/runnables';

const cascade: Runnable = withCascade({
  drafter, verifier,
});

const chain = cascade.pipe(new StringOutputParser());

Issue: Metadata Not Appearing

Symptom: No cascade metadata in responses

Solution: Check response_metadata

const result = await cascade.invoke('test');

// Access metadata correctly
console.log(result.response_metadata?.cascade);

// Not result.metadata (wrong)

Performance Metrics

Real-world results from production usage:

Next Steps

1. Examples: Check the examples/ directory for more patterns
2. API Reference: See the package README
3. LangSmith: Set up tracing for cost monitoring
4. Production: Read the production guide

Additional Resources

• LangChain Documentation
• cascadeflow Core Guide
• Cost Optimization Guide
• Performance Guide

Questions or Issues?

• GitHub: cascadeflow Issues
• Email: hello@lemony.ai