This one day transfer bonus is limited to 50,000 points and ranges from 25% to 100% based on your Bilt status. Platinum, Gold, Silver, and Blue get 100%, 75%, 50%, and 25% respectively.
The transfer bonus is live July 1st from Midnight ET until July 2nd, 2:59 AM ET. Transfer bonuses will be given on the first 50,000 Bilt Points transferred for each Bilt member. Cumulative transfers of more than 50,000 Bilt points to Alaska Airlines miles during the transfer window will not be bonused and will be processed as 1:1 transfers to Alaska Airlines miles.
Bilt, along with Marriott Bonvoy, is the only transfer partner to Alaska, though you can also get Mileage Plan miles from their credit card.
Note that July 1 is also the last day for Platinum and Gold members to activate Alaska Mileage Plan status through Dec 31 by transferring 10,000 points (which are not bonused). Platinum can get MVP Gold while Gold can get MVP.