This is a new neural machine translation concept introduced by Google, which is still in beta for end users.
This is what Google says about the current status of this product:
Access to the Google Cloud Translation API Premium Edition is available to customers on a case-by-case basis only. This is a Beta feature of the Google Cloud Translation API. This feature might be altered or changed in the future, and is not subject to any SLA or deprecation policy. This feature is not intended for real-time usage in critical applications.
Here is the sign-up form for those interested in using this.