Upload

await api.upload('/files', {
  file,
  fields: { albumId: '1' },
  onUploadProgress: ({ progress }) => setProgress(progress),
})

Or build FormData yourself:

import { createFormData } from 'tanstack-fetch'

const body = createFormData({ file, fields: { albumId: '1' } })
await api.post('/files', { body, onUploadProgress: … })

Progress uses XHR under the hood when onUploadProgress is set (fetch has no upload progress API).

Example: examples/file-upload