The deal was announced before New York's scheduled game against the Tampa Bay Rays was postponed due to a forecast of severe inclement weather. Gore was not added to the Yankees' 40-man roster, and will report to Triple-A Scranton/Wilkes-Barre.
The 5-foot-7 Gore is one of the fastest players in the majors and could be called up when major league rosters expand in September. He gives the AL East leaders a potential pinch-runner deluxe in the late innings of critical games -- perhaps even come playoff time in October.
"Obviously, depth and obviously a guy with a lot of speed that can play a certain role for you down the stretch," Yankees manager Aaron Boone said.
A right-handed hitter, the 28-year-old Gore was designated for assignment by the rebuilding Royals last week. He batted .275 (14 for 51) with 13 stolen bases in 18 attempts over a career-high 37 games for Kansas City this year. He has played in 100 games over six big league seasons, going 15 for 67 (.224) with 40 steals in 49 tries.
Gore swiped four bases in five attempts during the 2014 and `15 postseasons, doing his part to help the Royals win consecutive AL pennants and a World Series championship.