# @cosmjs/stream Agent Guide

> **Package**: `@cosmjs/stream` v0.38.0 **Purpose**: Reactive stream utilities
> **Layer**: Transport Layer

## Package Overview

Provides reactive stream utilities built on xstream for handling asynchronous
data flows. Used internally by `@cosmjs/tendermint-rpc` for WebSocket
subscriptions.

### Key Features

- **DefaultValueProducer**: Stream with default value
- **toListPromise**: Collect stream to array
- **firstEvent**: Get first event from stream
- **concat**: Combine streams

## Common Usage

```typescript
import { DefaultValueProducer, toListPromise } from "@cosmjs/stream";

// Create stream with default
const producer = new DefaultValueProducer(initialValue);
const stream = xs.create(producer);

// Collect all values
const values = await toListPromise(stream, 5); // Wait for 5 values

// Get first value
const first = await firstEvent(stream);
```

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**Last Updated**: January 6, 2026 **Package Version**: 0.38.0