HOKA UTMB Mont-Blanc / UTMB World Series 50K Final
OCC (Orsieres-Champex-Chamonix)
Orsieres → Chamonix
Race guide
Updated 19 July 2026
The OCC (Orsieres-Champex-Chamonix) is the sharpest entry point into the UTMB Mont-Blanc race week and the official UTMB World Series 50K Final. Covering 57 km from the Swiss village of Orsieres to the finish line on Chamonix's Rue du Docteur Paccard, it packs 3201 m of climbing into a course that crosses the French-Swiss border twice and crests at 2299 m. Do not be fooled by the 'short' distance relative to its famous siblings: the OCC is a technical, relentlessly vertical mountain race with a hard cut-off window of roughly 13 hours and 45 minutes that demands respect from even experienced ultrarunners. The race starts at 916 m in Orsieres and threads through iconic Alpine terrain — Champex-Lac, the Col de la Forclaz above Trient, Vallorcine, and the legendary Aiguilles Rouges traverse above Argentiere — before dropping into Chamonix at 1044 m. The course rewards runners who are equally strong climbers and technical descenders, and who can manage the sustained effort of a race that never truly flattens out.
Course & Terrain Overview
The OCC begins in the Swiss Valais at Orsieres (916 m) and immediately climbs toward the first checkpoint at Champex-Lac (8 km, 1465 m) — a gain of roughly 550 m in the opening 8 kilometres that sets the tone immediately. From Champex-Lac the route descends before a long climb carries runners over the high ground above Trient (24 km, 1326 m), where the course crosses into France. The climb to Vallorcine (35 km, 1940 m) is the highest checkpoint on the course and marks the point where the terrain becomes most exposed and rugged. Beyond Vallorcine, the course climbs again toward Argentiere (44 km, 1497 m) before tackling what many consider the defining section: the traverse above Argentiere to La Flegere (49 km, 1284 m) across the flanks of the Aiguilles Rouges. Trails throughout are a mix of forest singletrack, rocky Alpine paths and open ridgeline — technical underfoot and demanding on ankles and quads alike. The final descent from La Flegere drops over 200 m into Chamonix (57 km, 1044 m), finishing in the town centre under a packed crowd during peak UTMB week.
The Decisive Climbs & Descents
Three sections define where the OCC is won or lost. The first is the opening climb to Champex-Lac: with a cut-off at 10:30, runners who go out too hard on this ascent arrive at the first crew point already burning matches they will need later. The second decisive section is the approach to and departure from Vallorcine (1940 m, the course high point at 2299 m is reached on the climb into this zone) — this is the most committing part of the course, farthest from easy bail-out and fully exposed to whatever the weather is doing above the treeline. The third and most race-defining passage is the high traverse from Argentiere to La Flegere between kilometres 44 and 49. By this point runners have already covered 44 km and nearly all the accumulated climbing; legs are cooked and the rocky, undulating traverse offers no respite. The cut-off at La Flegere (20:25) gives just under two hours from Argentiere (cut-off 18:30) for a 5 km section that feels far longer in the late stages of the race. Descending sharply from La Flegere into Chamonix on tired legs requires controlled technique — blowing up the quads here, with the finish in sight, is one of the most common late-race mistakes.
Pacing & Fuelling Strategy
With 3201 m of climbing across 57 km, the OCC has an average gradient that demands a disciplined hike-run strategy on every significant ascent. The opening 8 km to Champex-Lac (cut-off 10:30) is the most important section to run conservatively — the climb is steep, the race has barely begun, and the real work comes in the second half. Use the rolling terrain between Champex-Lac and Trient (km 8–24) to find a sustainable rhythm; this stretch contains both descending and re-ascending and is where many runners try to bank time, often at a cost. Fuelling should be proactive from the gun. With crew access at Orsieres, Champex-Lac (8 km), Trient (24 km), Vallorcine (35 km) and Chamonix (finish), you have four opportunities to restock with crew support. Argentiere (44 km) and La Flegere (49 km) are aid-station-only checkpoints, so carry sufficient calories and fluid from Vallorcine to see you through the final 22 km. Given the altitude (cresting near 2299 m) and the effort level sustained over the Aiguilles Rouges traverse, solid food intake at Vallorcine is critical. Plan your cut-off buffer carefully: the gap from Trient (13:00) to Vallorcine (16:15) is 3 hours 15 minutes for 11 km that includes significant climbing — it is tighter than it looks on paper.
Conditions to Expect
The OCC takes place during UTMB Mont-Blanc week in late August, when the Mont-Blanc massif can deliver almost any weather within a single race day. Temperatures at the start in Orsieres may be mild or even warm, but the exposed sections above Vallorcine and across the Aiguilles Rouges can be significantly colder, especially if cloud rolls in or afternoon thunderstorms develop — both common in the Alps at this time of year. A waterproof jacket and mandatory kit are not optional formalities here. Snow on the higher sections is unusual in late August but not impossible after an early-season storm, and trails can be slippery on rocky or rooty descents even in dry conditions. The traverse section between Argentiere and La Flegere is particularly exposed to afternoon wind. Runners should expect the course to take longer than a flat 57 km equivalent and prepare mentally for the sustained effort of a true mountain race rather than a fast trail run. Headlamps are worth having accessible — the final cut-off at Chamonix is 22:45, meaning slower runners will finish in darkness.
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Checkpoints & cut-offs
✓ Course data verified against the official source (2026-07-05) · official source
0 km · 916 m · —
8.4 km · 1463 m · —
24.9 km · 1308 m · Thu 14:00
34.7 km · 2203 m · Thu 17:15
50.5 km · 1276 m · Thu 21:00
61.5 km · 1043 m · Thu 23:15
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