Chicago Manual of Style:

Q. When indicating possession of a word that ends in s, is it correct to repeat the s after using an apostrophe? For example, which is correct: “Dickens’ novel” or “Dickens’s novel”?

A. Either is correct, though we prefer the latter.

chicagomanualofstyle.org

New Yorker

AP

WaPo

NYRB

NYT

Sorry, but there is simply no debate. Not only both versions are correct, the one with extra s is the preferred one.