Apple Watch Ultra 4 Loses Marathon GPS Test to Coros

The Apple Watch Ultra 4 delivered the better smartwatch experience in a Frankfurt Marathon head-to-head, but the Coros Pace 4 Pro was the stronger endurance tool. Tom’s Guide found the Coros recorded a route closer to the official marathon distance, while also extending far beyond Apple on battery life. That is the split athletes need to understand: Apple remains compelling for daily connected life, but race-day simplicity still favors Coros.

Marathon accuracy favors Coros

At the Frankfurt Marathon, Tom’s Guide recorded 42.52km on the Coros Pace 4 Pro and 43.07km on the Apple Watch Ultra 4, against the official 42.19km course. A race is never run exactly on the measured line because runners weave, yet the tester was among the first 100 runners and said the Coros aligned more closely with course kilometer markers. The Apple also cut corners and placed the runner off-road more often in the skyscraper-lined city center.

That does not make the Ultra 4’s GPS poor across the board. The source says previous Apple Watch Ultra models have generally performed well in city centers. Still, this specific marathon matters because downtown buildings are exactly where satellite positioning can get messy. For runners following a pace target, distance drift can mean a misleading projected finish. The test’s Apple pacer mode predicted a 2:23 finish for an actual 2:25 marathon. Close enough for a casual run. Less comforting when every second is planned.

Heart-rate results were less decisive. Both watches use wrist optical sensors, which use light to estimate blood-volume changes, and the test included arm sleeves that may have affected readings. The tester felt the Apple’s trace looked more plausible, apart from a long gap between one and two hours when it could not secure a reading. Coros was consistent but appeared too high. For intervals, racing, and training zones, we agree with the source’s practical takeaway: use a chest strap when reliable heart rate matters. A strap reads the heart’s electrical signals through ECG, rather than optical blood-flow estimates at the wrist.

Battery, buttons and the smartwatch tradeoff

Coros won battery life cleanly. Tom’s Guide lists up to seven days with the always-on display for the Pace 4 Pro, versus 50 hours for the Ultra 4. After short runs on Friday and Saturday, the Coros was at 75% on Sunday morning and the Apple was at 41%. During the marathon, Coros lost 10%, while Apple lost 16% after about an hour of music playback. The Apple still lasted the weekend with one short charge, so this is not a failure. For multi-day travel, regular charging is simply more likely to remain part of the Ultra routine.

Apple fights back hard outside the start line. The Ultra 4 has an App Store, streaming-service music storage, NFC payments, boarding passes and deeper watch-face customization. Its titanium case also feels more premium, while the lighter Coros uses a sapphire crystal case and titanium bezel. In wet weather, though, Coros’s button-led operation is the more athletic design. Apple lets runners pause and lap with buttons, but ending a run requires the touchscreen. That is a small friction point until rain, sweat, gloves, or race fatigue arrive. We saw the same broader Apple-versus-budget-tracker distinction in our [Apple Watch 12, Oura Ring 5 and Fitbit Edge comparison](/en/articles/apple-watch-12-faces-oura-ring-5-and-fitbit-edge-2026-10-29).

What is missing is a clean answer on wrist heart-rate accuracy. No chest strap was worn as an ECG reference, and the sleeves complicated the comparison. Buyers should also watch pricing beyond this test: Gadgets & Wearables reports rising memory costs could pressure wearable makers in 2027, whether through higher prices, restrained storage upgrades, or fewer discounts. For now, the Pace 4 Pro is listed at $449 and the Ultra 4 at $799.

Verdict: choose the Coros Pace 4 Pro for marathon-focused training, button control and battery confidence. Choose the Apple Watch Ultra 4 if smartwatch features matter as much as sport, accepting that this race test gave Coros the better GPS result.