Rules and restrictions vary by route with travel ranging between late August and May.
Some routes are only valid for travel on Tuesdays, Wednesdays, and Saturdays, through November, while others will have scattered dates available on other days of the week throughout the year.
Peak holiday travel around Thanksgiving, Christmas, and New Year's will be much more expensive.
This sale is unadvertised and fares may jump at any moment. These are all big price drops, which normally don't last very long after falling this low. Secure your low fare by booking now and taking advantage of the 24-hour risk-free cancellation to think about your plans.
All fares work in the reverse direction as well. There may be more similar price drops. Check flights from your city to see today's current finds.
These are Basic Economy fares. On American, this includes a carry-on bag plus a small personal item. On United, this only includes one small personal item. A full-size carry-on bag is not allowed on United. A checked bag costs $30 each way on either airline.
Seats will be assigned at random upon check-in for these prices. You may pay a fee to choose a seat or choose to upgrade to the standard Economy fare.
It should cost around $70 more roundtrip for an upgrade to a standard or Main Cabin Economy fare. This will include a full-size carry-on bag on United. It will also include advanced seat selection and allow for ticket upgrades/ticket changes (fee applies) on both American and United. A checked bag is the same $30 fee each way.
As an example, I found a flight on American Airlines departing San Jose SJC on Wednesday, September 4, returning from Pittsburgh PIT on Saturday, September 7, for $136 roundtrip.