The new journey will take cyclists through scenic landscapes, with more than 5,000m (16,000ft) of climbing.
Although the event is only semi-supported, riders are backed by Red on Sports’ infrastructure and safety systems.
The new Ultra race will be the focus point of a weekend-long celebration of gravel cycling in southern Scotland.
Full details of the course will be revealed at a later date.
The Gralloch 2026 takes place from 15 to 17 May next year.