langchain-ai/langchainjs @langchain/core==1.0.0 on GitHub

🎉 LangChain v1.0 is here! This release provides a focused, production-ready foundation for building agents with significant improvements to the core abstractions and APIs. See the release notes for more details.

✨ Major Features

Standard content blocks

A new unified API for accessing modern LLM features across all providers:

New contentBlocks property: Provides provider-agnostic access to reasoning traces, citations, built-in tools (web search, code interpreters, etc.), and other advanced LLM features
Type-safe: Full TypeScript support with type hints for all content block types
Backward compatible: Content blocks can be loaded lazily with no breaking changes to existing code

Example:

const response = await model.invoke([
  { role: "user", content: "What is the weather in Tokyo?" },
]);

// Access structured content blocks
for (const block of response.contentBlocks) {
  if (block.type === "thinking") {
    console.log("Model reasoning:", block.thinking);
  } else if (block.type === "text") {
    console.log("Response:", block.text);
  }
}

For more information, see our guide on content blocks.

Enhanced Message API

Improvements to the core message types:

Structured content: Better support for multimodal content with the new content blocks API
Provider compatibility: Consistent message format across all LLM providers
Rich metadata: Enhanced metadata support for tracking message provenance and transformations

🔧 Improvements

Better structured output generation: Core abstractions for generating structured outputs in the main agent loop
Improved type safety: Enhanced TypeScript definitions across all core abstractions
Performance optimizations: Reduced overhead in message processing and runnable composition
Better error handling: More informative error messages and better error recovery

📦 Package Changes

The @langchain/core package remains focused on essential abstractions:

Core message types and content blocks
Base runnable abstractions
Tool definitions and schemas
Middleware infrastructure
Callback system
Output parsers
Prompt templates

🔄 Migration Notes

Backward Compatibility: This release maintains backward compatibility with existing code. Content blocks are loaded lazily, so no changes are required to existing applications.

New Features: To take advantage of new features like content blocks and middleware:

Update to @langchain/core@next:
```
npm install @langchain/core@1.0.0
```

Use the new contentBlocks property to access rich content:

const response = await model.invoke(messages);
console.log(response.contentBlocks); // New API
console.log(response.content); // Legacy API still works

For middleware and createAgent, install langchain@next:
```
npm install langchain@1.0.0 @langchain/core@1.0.0
```