The brand is keeping hush on how exactly you can score yourself a bottle but plans to give additional details on how and where you can do so tomorrow (I'll update accordingly here). They have revealed that the bottles will be available January 26, 2017, at participating restaurants nationwide but that quantities will vary by location.
While the giveaway is a first for us here in the States, McDonald's has given out and sold bottles of Big Mac sauce before over in Australia. If the giveaway goes over well, it's possible that they might offer the signature sauce in dipping cups like they do down under currently (given that they've tested Sriracha Mac sauce for dipping in the US last year).
Update 1/25/17 - The company has created an iMessage app (for iOS) that shows the nearest restaurant where the limited edition bottles will be available. Fans will need to go to participating restaurants starting tomorrow, January 26, 2017 and say the secret code "there’s a Big Mac for that" for a chance to get their hands on one of the bottles (first come, first served, while supplies last). You can find the app here.
If you don't happen to live by one of the participating restaurants, you also have a chance to win a bottle by following McDonald’s on Facebook, Instagram or Twitter, where, for the first time, the brand will be hosting a live giveaway.
Update 1/26/2017 - You can find the full list of participating locations on the McDonald's website here.
Photo via McDonald's.