Is it possible to define union types through Atlas GraphQL API

Is it possible to create a Union type in the MongoDB GraphQL API? E.g.

union SearchResult = Book | Author

type Book {
  title: String!

type Author {
  name: String!

type Query {
  search(contains: String): [SearchResult!]

Then query that union using inline fragments:

query GetSearchResults {
  search(contains: "Shakespeare") {
    ... on Book {
    ... on Author {

I have the need to return an array of two object types from a search query.