It has been reported on Flyertalk that United has rolled out an unannounced sale on roundtrip saver awards within the US, Alaska and Hawaii. (EDIT: Originally I thought the award sale included Canada, but that does not appear to be the case)

1. Domestic US awards: 25K (regular Saver roundtrip price) -> 20K (current promotional price)
2. Short-haul domestic US awards: 20K -> 16K
3. US to Hawaii: 45K -> 36K

(SEE ALSO: United’s incredibly deceptive award chart for Alaska)

Fine print on the United award sale

Because the fare sale is not officially announced anywhere (UPDATE: United has made it official on their site here), all of the details folks have been able to find have come through trial and error.  If you pick a trial fare from united.com (SEE ALSO: The trick to seeing more United award availability) and look at the fare rules, you’ll see that:

• TICKETS MUST BE ISSUED ON/BEFORE 23AUG 16.
• VALID FOR TRAVEL COMMENCING ON EACH TRIP ON/AFTER 23AUG 16. TRAVEL ON THIS FARE COMPONENT MUST COMMENCE BY MIDNIGHT ON 15DEC 16.
• TRAVEL IS NOT PERMITTED 22NOV 16 THROUGH 23NOV 16 OR 26NOV 16 THROUGH 28NOV 16

So you have to book by August 23rd, travel between August 23rd and December 15th, and blackout dates are Nov 22, 23, 26, 27, 28 (over Thanksgiving).  There is no need to enter a promotional code or anything – any roundtrip travel that fits the above criteria should automatically post at the lower levels.