No tour you can book online reaches the summit of Mont Blanc. Every day tour on the massif stops where the cable cars stop: 3,842 m at the Aiguille du Midi above Chamonix, or 3,466 m at Punta Helbronner above Courmayeur. The summit, 4,807 m, is an ascent on snow and ice with crampons, an ice axe and a rope, led by a mountain guide.
So most of this page is about the days you can book: the tours that include the Aiguille du Midi cable car, the Skyway on the Italian side, and the short guided days that put you on the glacier with a rope.