Why does my Azure OpenAI assistant creation call return a 400 'Unsupported data type' error?

Below is a checklist of things to verify in your assistant creation call, based on the current docs and known nuances with the beta endpoints:

1. Verify Deployment and Model Consistency

Make sure that your environment variable for DEPLOYMENT exactly matches the deployment name in your Azure portal that supports the model "gpt-4o" (or the intended model). In Azure OpenAI the deployment name (often matching an instance of a given model) must be valid—an incorrect deployment could trigger a data type or validation error.

2. Confirm Beta Endpoint and Access

The assistants API is still in beta and may require special headers and client support. For example, the documentation shows you need to pass headers like OpenAI-Beta: assistants=v2. Although the library’s beta client should handle this, confirm that your subscription or region has enabled access for the assistants API and the tools (code interpreter) you’re specifying.

3. Check the Format of Request Fields

The error “Unsupported data type” can sometimes indicate that one of the fields isn’t in the expected format. Double‑check:

• That instructions is a plain string.
• That your tools array is structured correctly. The docs provide an example with [{ type: "code_interpreter" }] so that should match.
• That any additional parameters are in the correct JSON types (strings or numbers).

4. Update the Client Library if Needed

Ensure you’re using the most recent version of the OpenAI client library. Sometimes beta endpoints require the latest changes from the library. An outdated client might be serializing data incorrectly.

5. JSON Mode Consideration

While your code isn’t directly triggering JSON mode output, if you plan to have the assistant produce JSON, remember that you must explicitly instruct the model (through a system or user message) to format its output as JSON. This point, however, relates more to the assistant’s responses rather than the creation call.

Example Revised Code

Below is an annotated snippet that highlights potential areas to check:

JAVASCRIPTCopied
const dotenv = require("dotenv");
dotenv.config();

const { AzureOpenAI } = require("openai");

const endpoint = process.env["AZURE_OPENAI_ENDPOINT"];
const apiKey = process.env["AZURE_OPENAI_API_KEY"];
const apiVersion = process.env["API_VERSION"];
const deployment = process.env["DEPLOYMENT"]; // Ensure this exactly matches a valid deployment

const client = new AzureOpenAI({ endpoint, apiKey, apiVersion, deployment });

async function main() {
  try {
    const assistant = await client.beta.assistants.create({
      name: "Math Tutor",
      instructions: "You are a personal math tutor. Write and run code to answer math questions.",
      tools: [{ type: "code_interpreter" }],
      model: "gpt-4o", // Confirm that this model matches your deployment's model
    });
    console.log("Assistant created successfully:", assistant);
  } catch (error) {
    console.error("Error creating assistant:", error);
  }
}

main();

Final Thoughts

• Double-check your Azure deployment: If your chat completions work but not the assistant creation, the issue might be with the beta assistant API configuration.
• Review your access permissions: Validate that your subscription and region support the assistants endpoint and the additional tools (e.g., code interpreter).

By reviewing these points and ensuring that your deployment, model, and client package are in sync with the Azure OpenAI documentation, you should be able to resolve the "Unsupported data type" error.