adj. Not susceptible to or experiencing computer problems related to the changeover from 1999 to 2000.
Trying to sum up a worldwide story in one headline seemed too
much for some newspapers, which stuck with numbers instead: The
New York Times used "1/1/00," and The Washington Post
and the New York Daily News chose "2000."

"Y2OK," the Chicago Sun-Times said.
—Martha T. Moore, “ There was no crisis, but it was still a good story,” USA Today, January 03, 2000
After a year of computer-bug fears and a month of terrorism warnings, everything was Y2OK.
—Joel Stein, “Hey, You In That Bunker, You Can Come Out Now!,” Time, January 01, 2000
1999 (earliest)
—Stephen Power, “Gramm says Texas banks Y2OK,” The Dallas Morning News, February 14, 1999