Key points below
You can see the rest of the changes at the link above.
ST. PETERSBURG, Fla. -- Minor League Baseball today announced rule and procedure changes aimed at reducing the length of extra innings games and the number of mound visits during a game throughout Minor League Baseball. In addition, the Triple-A and Double-A levels will use a 15-second pitch clock with no runners on base.
The procedures, created in partnership with Major League Baseball, aim to reduce the number of pitchers used in extra innings and the issues created by extra innings games, including, but not limited to, shortages of pitchers in the days to follow, the use of position players as pitchers and the transferring of players between affiliates due to pitching shortages caused by extra innings games.
"We believe these changes to extra innings will enhance the fans' enjoyment of the game and will become something that the fans will look forward to on nights where the game is tied late in the contest," said Minor League Baseball President Pat O'Conner. "Player safety has been an area of growing concern for our partners at the Major League Baseball level, and the impact that lengthy extra innings games has on pitchers, position players and an entire organization was something that needed to be addressed
https://www.milb.com/milb/news/minor-league-baseball-announces-pace-of-play-regulations-for-2018/c-268683294At all levels of Minor League Baseball, extra innings will begin with a runner on second base. The runner at second base will be the player in the batting order position previous to the leadoff batter of the inning (or a substitute for that player). By way of example, if the number five hitter in the batting order is due to lead off the 10th inning, the number four player in the batting order (or a pinch-runner for such player) shall begin the inning on second base. Any runner or batter removed from the game for a substitute shall be ineligible to return to the game, as is the case in all circumstances under the Official Baseball Rules.
For purposes of calculating earned runs under Rule 9.16, the runner who begins an inning on second base pursuant to this rule shall be deemed to be a runner who has reached second base because of a fielding error, but no error shall be charged to the opposing team or to any player.
You can see the rest of the changes at the link above.