**The 2026 MLB regular season's longest winning streak stands at 15 games by the Boston Red Sox in July, with no team approaching that mark in the months since.** This positions the 13-15 games outcome as the clear trader consensus at 95.9% implied probability. Multiple sources confirm the Red Sox streak as the season high, tying a franchise record and ranking among the longer runs in the expansion era. Subsequent streaks have topped out around 9-10 games (e.g., Cubs, Phillies, Rays, Royals), and current active streaks as of early September remain short (Red Sox at 5, Dodgers at 4). With roughly three weeks remaining, the combination of late-season fatigue, tougher matchups for contenders, and the historical scarcity of 16+ game streaks supports the heavy weighting toward 13-15. Scenarios that could shift odds include an unexpected late surge by a playoff-bound club with favorable scheduling and healthy pitching staff, though such runs have proven rare this year.