It’s for travel starting September 3rd and runs through February. Sample one-way fares:
The fares are good in both directions and I do see plenty of availability, though usually not on key heavy travel days like Monday and Friday. If you have some flexibility in travel dates these are reasonably good prices.
For example, a route I travel often is IAD-LAX. While I can typically find flights under $400 if I book ahead of time, I don’t see $300 RT fares on that route very often.
As of right now, I don’t see the legacy carriers matching this fare sale, but it just came out. Check in a couple hours if your preferred routes are being price-matched.