Historically we have included the ID field in account objects returned from the new account endpoints. This is non-standard and can be slightly confusing given RFC 8555 specifies that clients should learn the account ID (and resource URL) from the Location header in the returned response.
We are planning on removing this field going forward as to bring our implementation more in line with RFC 8555. Our current plan is to enable this behavior change in the staging environment next week (week of June 3rd) and if there are no significant client breakages we will then disable it in our production environment in a months time (week of July 3rd).