> ## Documentation Index
> Fetch the complete documentation index at: https://docs.cascadeflow.ai/llms.txt
> Use this file to discover all available pages before exploring further.

# @cascadeflow/langchain

> TypeScript LangChain integration with withCascade() for drop-in cascade routing and model discovery helpers.

LangChain integration for TypeScript. Provides `withCascade()` for drop-in cascade routing with any LangChain chat model.

## Install

```bash theme={null}
npm install @cascadeflow/langchain @langchain/core @langchain/openai
```

## withCascade

Creates a cascade-enabled chat model from a drafter and verifier.

```typescript theme={null}
import { ChatOpenAI } from '@langchain/openai';
import { ChatAnthropic } from '@langchain/anthropic';
import { withCascade } from '@cascadeflow/langchain';

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

// Use like any LangChain chat model
const result = await cascade.invoke('Explain quantum computing');

// With LCEL chains
const chain = prompt.pipe(cascade).pipe(new StringOutputParser());
```

## Options

```typescript theme={null}
interface CascadeOptions {
  drafter: BaseChatModel;        // Cheap, fast model
  verifier: BaseChatModel;       // Powerful fallback model
  qualityThreshold?: number;     // 0-1, default 0.4
}
```

## Model Discovery

```typescript theme={null}
import {
  discoverCascadePairs,
  findBestCascadePair,
  analyzeModel,
  validateCascadePair,
} from '@cascadeflow/langchain';

const models = [
  new ChatOpenAI({ model: 'gpt-4o-mini' }),
  new ChatOpenAI({ model: 'gpt-4o' }),
  new ChatAnthropic({ model: 'claude-sonnet-4' }),
];

const best = findBestCascadePair(models);
const cascade = withCascade({
  drafter: best.drafter,
  verifier: best.verifier,
});
```

## Features

* Full LCEL support (pipes, sequences, batch)
* Streaming with pre-routing
* Tool calling and structured output
* LangSmith cost tracking metadata
* Model discovery and pair validation