Hilton has officially announced that most Citi Honors card accounts will be sold to American Express, and transferred January 30, 2018. Reserve accounts will become American Express Honors Ascend accounts. (Ascend is rebranded Surpass.) The criteria for selecting accounts eligible for transfer to American Express are unpublished, but it's possible that if you already hold a Surpass card your account will remain at Citi, and that Citi will convert it to a ThankYou or cashback card.
Hilton FAQ is here:
http://hiltonhonors3.hilton.com/en/e...-card-faq.html
Hilton forum thread:
American Express Announces Two New Hilton Credit Cards