MLB approves automated ball/strike system for 2026 season

New York — Major League Baseball will introduce robot umpires in 2026 through the Automated Ball/Strike System, after the league’s 11-person competition committee approved a framework that uses a challenge-based approach with a human on the field. Under the plan, the initial call on every pitch will be made by the human umpire, with each team allowed to challenge calls to consult the computer system.

Under ABS, teams will be allowed two challenges per game. If a challenge is unsuccessful, the team loses the challenge; if a challenge is successful, the team retains the challenge and can use it later in the game. In extra innings, a team will receive one additional challenge in each inning. Only a batter, pitcher or catcher may initiate a challenge by signaling with the tap of a helmet or cap, and the dugout cannot provide assistance. A challenge must be made within two seconds, after which the visual of the pitch and the strike zone is displayed on the scoreboard and broadcast feed. The umpire then announces the updated count.

MLB estimates the review process averages about 17 seconds. A Hawk-Eye style pose-tracking system uses cameras to determine whether pitches cross home plate within the designated zone, with the strike zone based on the height of each batter who is measured without shoes before the team’s first test game. The ABS strike zone is a rectangle anchored to the plate’s midpoint rather than the oval shape often observed in the traditional call, and the strike zone is determined from the midpoint of the plate, 8 1/2 inches from the front and 8 1/2 inches from the back. The rectangle is used to render the final decision, while the traditional rule book defines the zone as a cube with rules governing height and width. The system has drawn attention for how the strike zone is defined and adjusted as calibrations advance.

The ABS is designed to run alongside the human umpire, who will still call balls and strikes in real time, with the computer providing a second look and a potential overturn via challenges. The shape and size of the automated zone have been the subject of ongoing discussion and calibration since the concept first emerged. MLB has adjusted the width of the zone several times since it began testing in 2022, moving from a 19-inch width to 17 inches to align with the width of home plate. The league has emphasized that the ABS strike zone is a rectangle while the on-field strike zone called by umpires in the field is determined by the rule book as a cube.

The strike zone in ABS is defined in part by measurements drawn from the batter’s height, which is standardized during testing. The height of the strike zone is determined by the batter’s height, measured without shoes; the system does not use the batter’s stance as a factor. The goal is to create a consistent, computer-driven zone that can be applied uniformly across all parks and games, with ongoing calibrations as more data accumulate.

The ABS has been tested in the minor leagues since 2019 and has undergone multiple levels of trial. Independent leagues piloted the technology early on, including the Atlantic League in 2019. MLB installed the system for the Arizona Fall League that same year. The system moved up through the ranks in the following years: eight of nine ballparks in the Low-A Southeast League used it in 2021, then it progressed to Triple-A in 2022. At Triple-A at the start of the 2023 season, half the games used the robots for ball/strike calls, while the other half relied on a human making decisions subject to appeals by the ABS. In June 2024, MLB shifted Triple-A to an all-challenge system, and the ABS was used this year at 13 spring training ballparks hosting 19 teams in 288 exhibition games.

The early results across trials have been mixed but informative. In spring training exhibitions this year, teams won 52.2% of their ball/strike challenges (617 of 1,182). At the All-Star Game in Atlanta, four of five plate-umpire challenges were successful, signaling that the system can produce meaningful adjustments in real time. Overall, the success rate for challenges has hovered around 50% in the minor leagues, with the more frequent challenges often coming from defenses, such as catchers.

In Triple-A this season, the success rate of challenges edged down to 49.5% from 50.6% in the previous year. Defenses have historically been more successful than hitters in the challenge environment, winning about 53.7% of games’ challenges compared with roughly 45% by batters. The rate of challenges rose during the course of games, with overall challenges averaging 4.2 per game this season, up from 3.9 per game in the earlier period.

Looking at per-game and per-plate appearance data provides a sense of how often managers and catchers deploy challenges in an ABS world. In 2024 at Triple-A, first-pitch challenges comprised just 1.6% of pitches, but the rate climbed with two-strike and full-count situations, at 3.9% and 8.2% respectively. Challenge usage tended to rise later in games, with 1.9% challenged in the first three innings versus 3.6% in the later innings. The trend lines suggest teams use challenges more as the game progresses and as the stakes increase.

Industry observers note that the ABS is designed to complement, not supplant, the on-field umpire’s judgment. The league has indicated that calibration will continue, with ongoing data gathering from spring training and minor leagues feeding adjustments to the mechanism and the zone’s interpretation. MLB has signaled that the ABS, including its challenge format and strike-zone definition, will continue to evolve as officials and technology work to refine accuracy and consistency before a full adoption in 2026.

The system’s cross-family testing has shown that accuracy improved overall when the computer review is available, while the human element remains critical for context around pitches that fall outside the strict boundaries of the automated zone. Umpire performance in detecting borderline pitches remains high, but the ABS offers a consistent baseline that can reduce some subjective variability across parks and crews. MLB’s continued emphasis on transparency will include the public display of the pitch graphic and zone on scoreboard and broadcast feeds, helping fans understand the decision process in real time.

The league has underscored that the ABS will be implemented in stages, starting with a controlled rollout in the 2026 season, with ongoing adjustments based on data from spring training and the minor-league trials. The goal is to stabilize the system, improve accuracy, and ensure that the human element remains central to the game while leveraging technology to enhance fairness and efficiency. As theabs framework moves toward widespread use, teams and players will adapt to the new rhythm of challenges and reviews, and fans will see a more uniform strike zone across ballparks.