If you buy a cheaper first class award fare with a connection and the schedule changes allow you to switch the flight, they will let you switch to a Delta One flight at no extra cost. I did this earlier this year and was able to switch to ATL to HNL D1 for 75,000 miles in the app when directly booking the Delta One cost around 300,000 miles. Granted this was earlier this year so I'm not sure if they quietly changed the rules allowing this.