The Short Version
Apple Watch Ultra 3 recorded 26.54 miles and Garmin Forerunner 570 logged 26.57 miles during the 2026 London Marathon, both within 0.35 miles of the official 26.219-mile course.
Apple Watch Ultra 3 tracked 26.54 miles at the London Marathon, Garmin logged 26.57, a difference smaller than a city block. Through one of GPS's worst dead zones, both watches basically tied. Garmin still wins for serious runners who want deep training data. Apple wins for everyone else who also wants to answer texts.
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