Multimodal Content

A message part can carry an image, audio clip, video, or PDF. The model then answers about that file.

Make the content of the message an array of parts. One part holds the text, and the other parts hold the image, audio, video, or document.

Quick setup

This setup lets a user pick an image and ask about it. It takes about 5 minutes.

1. Use a model that reads images

Your chat route does not change. Pick a model that takes image input:

// api/chat.ts
import {
  chat,
  chatParamsFromRequest,
  toServerSentEventsResponse,
} from "@tanstack/ai";
import { openaiText } from "@tanstack/ai-openai";

export async function POST(request: Request) {
  const { messages, threadId, runId } = await chatParamsFromRequest(request);

  const stream = chat({
    adapter: openaiText("gpt-6.1-sol"),
    messages,
    threadId,
    runId,
  });

  return toServerSentEventsResponse(stream);
}

2. Send the image from the browser

Read the file as base64. Then send a text part and an image part together:

tsx

import { useChat, fetchServerSentEvents } from "@tanstack/ai-react";

function readAsBase64(file: File): Promise<string> {
  return new Promise((resolve, reject) => {
    const reader = new FileReader();
    reader.onload = () => {
      const result = reader.result;
      if (typeof result !== "string") {
        reject(new Error("Could not read the file"));
        return;
      }
      // Remove the "data:image/png;base64," prefix.
      resolve(result.slice(result.indexOf(",") + 1));
    };
    reader.onerror = () => reject(reader.error);
    reader.readAsDataURL(file);
  });
}

export function AskAboutImage() {
  const { sendMessage } = useChat({
    connection: fetchServerSentEvents("/api/chat"),
    threadId: "support-chat",
  });

  async function send(file: File) {
    const base64 = await readAsBase64(file);
    await sendMessage({
      content: [
        { type: "text", content: "What is in this image?" },
        {
          type: "image",
          source: { type: "data", value: base64, mimeType: file.type },
        },
      ],
    });
  }

  return (
    <input
      type="file"
      accept="image/*"
      onChange={(event) => {
        const file = event.target.files?.[0];
        if (file) void send(file);
      }}
    />
  );
}

Pick an image, and the model describes it in the chat.

How it works

content is a string or an array of parts. A string is the same as one text part.
Each part has a type: text, image, audio, video, or document.
Each media part has a source that says where the bytes are. See Source types.
The adapter turns each part into the format of its provider.
The types of chat() allow only the input types that the selected model supports.

Advanced

Content parts

The part types come from @tanstack/ai:

import type { ImagePart, TextPart } from "@tanstack/ai";

const textPart: TextPart = {
  type: "text",
  content: "What do you see in this image?",
};

// Image from base64 data. `mimeType` is required for data sources.
const imagePart: ImagePart = {
  type: "image",
  source: {
    type: "data",
    value: "base64EncodedImageData...",
    mimeType: "image/jpeg",
  },
  metadata: {
    detail: "high", // OpenAI detail level
  },
};

// Image from a URL. `mimeType` is optional for URL sources.
const imageUrlPart: ImagePart = {
  type: "image",
  source: {
    type: "url",
    value: "https://example.com/image.jpg",
    mimeType: "image/jpeg",
  },
};

All the part types:

import type {
  AudioPart,
  ContentPart,
  DocumentPart,
  ImagePart,
  TextPart,
  VideoPart,
} from "@tanstack/ai";

// Metadata types for each provider
import type { OpenAIImageMetadata } from "@tanstack/ai-openai";
import type { AnthropicImageMetadata } from "@tanstack/ai-anthropic";
import type { GeminiImageMetadata } from "@tanstack/ai-gemini";

On the server, you can build the same message in a chat() call:

import { chat } from "@tanstack/ai";
import { openaiText } from "@tanstack/ai-openai";

const stream = chat({
  adapter: openaiText("gpt-6.1-sol"),
  messages: [
    {
      role: "user",
      content: [
        { type: "text", content: "What is in this image?" },
        {
          type: "image",
          source: { type: "url", value: "https://example.com/photo.jpg" },
        },
      ],
    },
  ],
  threadId: "thread-1",
});

Source types

Each media part has one of three sources.

Data (base64)

Use type: 'data' for inline base64 bytes. The mimeType field is required, so the provider gets the correct content type:

import type { AudioPart, ImagePart } from "@tanstack/ai";

const imagePart: ImagePart = {
  type: "image",
  source: {
    type: "data",
    value: "iVBORw0KGgoAAAANSUhEUgAAAAUA...",
    mimeType: "image/png",
  },
};

const audioPart: AudioPart = {
  type: "audio",
  source: {
    type: "data",
    value: "base64AudioData...",
    mimeType: "audio/mp3",
  },
};

Data is good for small files, or when the file is not on a public URL.

URL

Use type: 'url' for a file at a URL. The mimeType field is optional, because the provider can often find the type from the URL or the response headers:

import type { ImagePart } from "@tanstack/ai";

const imagePart: ImagePart = {
  type: "image",
  source: {
    type: "url",
    value: "https://example.com/image.jpg",
    mimeType: "image/jpeg",
  },
};

A URL is good for large files that are already online. Not all providers accept a URL for all input types. Read the provider docs.

File handle (Files API)

Use type: 'file' for a file that you uploaded one time with the Files API of a provider. The provider keeps the bytes, and each request sends a small reference. The source holds the opaque handle and the provider that issued it: { type: 'file', value: 'file-...', provider: 'openai' }.

import { chat, fileSourceFromHandle, uploadFile } from "@tanstack/ai";
import { openaiFiles, openaiText } from "@tanstack/ai-openai";
import { pdfBase64 } from "./pdf-data";

// Upload one time.
const handle = await uploadFile({
  adapter: openaiFiles(),
  input: { data: pdfBase64, mimeType: "application/pdf" },
});

// Then use the handle in as many requests as you want.
const stream = chat({
  adapter: openaiText("gpt-5.5"),
  messages: [
    {
      role: "user",
      content: [
        { type: "text", content: "Summarize this document" },
        { type: "document", source: fileSourceFromHandle(handle) },
      ],
    },
  ],
  threadId: "thread-1",
});

What fileSourceFromHandle(handle) does:

It builds the { type: 'file', value, provider } source.
It picks the handle URL for Gemini, fal, and Grok, and the opaque id for OpenAI and Anthropic.
Each adapter maps value to the native field of the provider (file_id, fileData.fileUri, or a URL).

These cases throw an error:

A handle that you send to a different provider.
A handle that you send to an adapter with no Files API support. The adapter rejects it before it builds the request.
A handle that you send to an endpoint that needs the bytes, such as image edits or Veo.

See Files API to upload, get, and delete handles.

Images in tool results

A tool can return an array of ContentPart. Use it to give the model a screenshot or a chart:

import { toolDefinition } from "@tanstack/ai";
import type { ContentPart } from "@tanstack/ai";
import { z } from "zod";

const getScreenshot = toolDefinition({
  name: "get_screenshot",
  description: "Get a screenshot of the page",
  inputSchema: z.object({}),
}).server(async (): Promise<Array<ContentPart>> => [
  { type: "text", content: "Page screenshot" },
  {
    type: "image",
    source: { type: "data", value: "iVBORw0KGgo...", mimeType: "image/png" },
  },
]);

The adapter sends the image in the form that its API accepts:

Responses APIs (openaiText, openRouterResponsesText): the image stays in the tool output.
Chat Completions APIs (openRouterText, openaiChatCompletions, and the other Chat Completions adapters built on @tanstack/openai-base): a tool message holds text only. The text goes in the tool message. The images go in one user message after the tool results. If a result has only images, its tool text is (see attached image).

Some more rules:

If these adapters know that the model has no image input, they do not send the images.
An adapter that does not know the input types of the model sends the images. A result with only images then has the text (image omitted: this model has no image input).
The Chat Completions adapters and openRouterResponsesText send only the text and the images of a result that has images. They do not send audio, video, or documents from it.
When an adapter sends an image from a tool result, a file source is an error, except on openaiText. Use a data or url source.

Provider support

Provider	Adapter	Input besides text
OpenAI	openaiText	Image on gpt-6.1-sol and most new models. Image and PDF document on gpt-5.5. Audio on gpt-audio.
Anthropic	anthropicText	Image and PDF document on all Claude models, for example claude-sonnet-5-5.
Gemini	geminiText	Image, audio, video, and document, for example on gemini-3.8-flash.
Ollama	ollamaText	Image on vision models, such as llama3.2-vision. Support changes by model.

For the full list of each model, read supports.input in the model-meta.ts file of the adapter package.

ollamaText(model) reads the host from the OLLAMA_HOST environment variable. The default is http://localhost:11434.

OpenAI image detail and PDF filename

OpenAI reads two metadata fields:

detail on an image: 'auto', 'low', or 'high'.
filename on a document. The API needs a filename with inline data. The default is document.pdf.

import { chat } from "@tanstack/ai";
import { openaiText } from "@tanstack/ai-openai";
import { imageBase64, pdfBase64 } from "./data";

const stream = chat({
  adapter: openaiText("gpt-5.5"),
  messages: [
    {
      role: "user",
      content: [
        { type: "text", content: "Does the chart match the report?" },
        {
          type: "image",
          source: { type: "data", value: imageBase64, mimeType: "image/jpeg" },
          metadata: { detail: "high" },
        },
        {
          type: "document",
          source: { type: "data", value: pdfBase64, mimeType: "application/pdf" },
          metadata: { filename: "report.pdf" },
        },
      ],
    },
  ],
  threadId: "thread-1",
});

Send any file type from the browser

This input accepts images, audio, video, and PDFs. It picks the part type from the MIME type of the file. It uses readAsBase64 from the quick setup:

tsx

import { useChat, fetchServerSentEvents } from "@tanstack/ai-react";
import { readAsBase64 } from "./read-as-base64";

export function ChatWithFileUpload() {
  const { sendMessage } = useChat({
    connection: fetchServerSentEvents("/api/chat"),
    threadId: "support-chat",
  });

  async function handleFileUpload(file: File) {
    const base64 = await readAsBase64(file);

    const type = file.type.startsWith("image/")
      ? "image"
      : file.type.startsWith("audio/")
        ? "audio"
        : file.type.startsWith("video/")
          ? "video"
          : "document";

    await sendMessage({
      content: [
        { type: "text", content: `Please analyze this ${type}` },
        {
          type,
          source: { type: "data", value: base64, mimeType: file.type },
        },
      ],
    });
  }

  return (
    <input
      type="file"
      accept="image/*,audio/*,video/*,.pdf"
      onChange={(event) => {
        const file = event.target.files?.[0];
        if (file) void handleFileUpload(file);
      }}
    />
  );
}

The model on the server must accept each type that you allow here.

Message ID and per-message props

sendMessage takes a string or a MultimodalContent object. These examples use ChatClient from @tanstack/ai-client. The sendMessage of useChat takes the same first argument. For per-message props, it takes { body } as the second argument.

Give the message your own ID:

import { ChatClient, fetchServerSentEvents } from "@tanstack/ai-client";

const client = new ChatClient({
  connection: fetchServerSentEvents("/api/chat"),
  threadId: "support-chat",
});

await client.sendMessage({
  content: "Hello!",
  id: "custom-message-id-123",
});

The second argument adds forwardedProps for that one request. They are shallow-merged with the base forwardedProps of the client, and the values of the message win:

import { ChatClient, fetchServerSentEvents } from "@tanstack/ai-client";

const client = new ChatClient({
  connection: fetchServerSentEvents("/api/chat"),
  threadId: "support-chat",
  forwardedProps: { model: "gpt-6.1-sol" },
});

await client.sendMessage("Analyze this complex problem", {
  temperature: 0.2,
});

Validate messages from a request

request.json() returns any. TanStack AI does not ship a runtime message validator. Define a schema with a Standard Schema library (Zod, Valibot, ArkType, and more), and parse the body before you give it to chat():

import { chat } from "@tanstack/ai";
import { openaiText } from "@tanstack/ai-openai";
import { z } from "zod";

const ContentPartSchema = z.discriminatedUnion("type", [
  z.object({ type: z.literal("text"), content: z.string() }),
  z.object({
    type: z.literal("image"),
    source: z.object({ type: z.enum(["url", "data"]), value: z.string() }),
  }),
]);

const MessageSchema = z.object({
  // `ModelMessage.role` is 'user' | 'assistant' | 'tool'. There is no
  // 'system' role. Pass system instructions with the `systemPrompts`
  // option of `chat()`.
  role: z.enum(["user", "assistant", "tool"]),
  content: z.union([z.string(), z.array(ContentPartSchema)]),
});

const BodySchema = z.object({
  messages: z.array(MessageSchema),
  threadId: z.string(),
});

// In an API route handler
const { messages, threadId } = BodySchema.parse(await request.json());

const stream = chat({
  adapter: openaiText("gpt-6.1-sol"),
  messages,
  threadId,
});