SDK message types don't support @langchain/core v1 ContentBlock formats

[mingxuan-he]

Checked other resources

• I added a very descriptive title to this issue.
• I searched the LangGraph.js documentation with the integrated search.
• I used the GitHub search to find a similar question and didn't find it.
• I am sure that this is a bug in LangGraph.js rather than my code.
• The bug is not resolved by updating to the latest stable version of LangGraph (or the specific integration package).

Example Code

import { Message } from "@langchain/langgraph-sdk";
import { HumanMessage } from "@langchain/core/messages";

// This works with SDK
const sdkCompatibleMessage: Message = {
  type: "human",
  content: [
    { type: "text", text: "Hello" },
    { type: "image_url", image_url: { url: "https://example.com/image.png" } }
  ]
};

// This is the newer @langchain/core v1 ContentBlock.Multimodal.Image format
// but not supported by the SDK's MessageContentComplex types
const coreV1ImageBlock = {
  type: "image" as const,
  url: "https://example.com/image.png",
  mimeType: "image/png"
};

// This assignment would fail because the SDK doesn't recognize "image" type
// const sdkMessageWithCoreTypes: Message = {
//   type: "human",
//   content: [coreV1ImageBlock]  // ❌ Type error here
// };

Error Message and Stack Trace (if applicable)

Type '{ type: "image"; url: string; mimeType: string; }' is not assignable to type 'MessageContentComplex'.
Type '{ type: "image"; url: string; mimeType: string; }' is not assignable to type 'MessageContentText'.
Type '{ type: "image"; url: string; mimeType: string; }' is not assignable to type 'MessageContentImageUrl'.
Property 'image_url' is missing in type '{ type: "image"; url: string; mimeType: string; }' but required in type 'MessageContentImageUrl'.

Where MessageContentComplex is defined as:

type MessageContentComplex = MessageContentText | MessageContentImageUrl;

// MessageContentText = { type: "text"; text: string; }
// MessageContentImageUrl = { type: "image_url"; image_url: string | { url: string; detail?: ImageDetail } }

And @langchain/core ContentBlock.Multimodal.Image is:

type Image = Data & {
  readonly type: "image";  // ❌ Not supported by SDK
  // Plus Data properties: mimeType?, url?, data?, fileId?, etc.
}

Description

The @langchain/langgraph-sdk package only supports OpenAI-style message content blocks (text and image_url), but the newer @langchain/core v1 package introduces a more comprehensive ContentBlock format that includes image, file, video, and other multimodal content types.

This creates a type mismatch where developers using the latest @langchain/core ContentBlock types cannot use them directly with the langgraph SDK without type assertions or conversions.

System Info

• Package: @langchain/langgraph-sdk@1.3.1
• @langchain/core: 1.1.8
• Platform: macOS
• Node version: 20.11.1
• Package Manager: npm 10.2.4

Package Info:

frontend-react@0.0.0 /path/to/project
├── @langchain/core@1.1.8
└── @langchain/langgraph-sdk@1.3.1