Programmatically adding reference arrays in Sanity with correct _type

Looking at the official Sanity documentation on creating references programmatically, you should indeed use _type: 'reference' when creating references programmatically, exactly as documented.

However, the real issue you're experiencing is almost certainly related to the missing _key field, not the _type field. Every item in a Sanity array requires a unique _key, and this is what's likely causing your Desk tool errors.

Here's the correct way to add reference arrays programmatically:

import {randomKey} from '@sanity/util/content'

const patch = await sanityClient
  .patch(auction._id)
  .set({ creators: [] })
  .append('creators', [{ 
    _type: 'reference', 
    _ref: creator._id,
    _key: randomKey(12)  // This is crucial!
  }])
  .commit();

Or enable automatic key generation in your client configuration:

import {createClient} from '@sanity/client'

const sanityClient = createClient({
  projectId: 'your-project-id',
  dataset: 'your-dataset-name',
  useCdn: false,
  apiVersion: '2023-05-03',
  token: process.env.SANITY_SECRET_TOKEN,
  autoGenerateArrayKeys: true  // This handles _key automatically
})

Why you saw _type: 'creator' in Studio:

When you inspected the UI-created reference and saw _type: 'creator', you may have been looking at a dereferenced version or a display artifact in Studio. The actual stored data format uses _type: 'reference' as specified in the reference type documentation.

There's also a scenario where _type would be the document type: if your schema allows references to multiple document types in an array, but that doesn't appear to be your case based on your description.

Summary: Stick with _type: 'reference' as documented, but make sure you're either manually adding _key fields or enabling autoGenerateArrayKeys: true. The missing _key is what's breaking things, and enabling auto-generation (as you discovered in your edits) is what made it work.