For flights we use a serial Twin Astir G103 glider, below are its characteristics:

Grob G-103 Twin Astir
For Russian people, the "full" name of the glider is heartbreaking. Who decides to fly on a coffin? I assure you that this aircraft has nothing to do with funeral affairs and wooden macs. From German, grob is translated as rough. It is possible that the ancestors of Dr. Burkhart Grob, founder of Grob Aerospace, were involved in the mill business.
Grob Aerospace initially built the Cirrus Standard under the Schempp-Hirth license, but after gaining experience with composite materials  in 1974 began testing the Astir CS airframe, a single-seat club-class airframe. And on the basis of Astir, one of the world's first two-seat gliders made of fiberglass was designed - Twin Astir, which made its first flight on December 31, 1976.
World records were also set on Grob gliders. The record of the American glider pilot Robert Harris is mentioned in Wikipedia in an article about the glider G-102 Astir. In 1986 he set a world record for single-seat gliders of 14,938 meters.
On the G-103 Twin Astir SL glider, Ingrid Köhler and Shahla Klass set a world altitude record (8782 meters) in the class of two-seater gliders with engine. In 1993 that record was canceled due to changes in the sporting code of the International Aeronautical Federation.
The Stratus project did not have a special choice of the type of glider, but it is all the more remarkable that the G-103 Twin Astir was originally positioned as a training glider, and you probably remember that the current Russia national record was also set on a training glider - on the legendary glider Let L-13 Blanik.