Wysilab.

Instant Terra: a new generation of software dedicated to creating terrains in real
time for the most ambitious projects
Instant Terra is the highest-performance terrain-creation tool on the market since
2018. It is currently used in several undisclosed AAA projects by some of the
major video game studios worldwide.
Instant Terrain is a non-destructive, procedural software using a deterministic
process. It adds fluidity to artists' work and increases project productivity.
The Instant Terra Pro edition offers an additional Python & C# API for automation
and a C++ API for a live link with your tools.