Cycles OptiX multi‑GPU device limit configuration

The goal is to enable Cycles rendering with the OptiX backend on three or more identical NVIDIA RTX GPUs so that memory and compute resources scale across all devices.

Official documentation does not state a maximum number of GPUs that can be used simultaneously with OptiX, and user reports suggest that enabling more than two GPUs may cause Cycles to fall back to single‑GPU mode or exhibit unstable memory usage. It remains unclear whether this behavior is an intentional driver‑level restriction or an unresolved bug in the OptiX integration.

What is the maximum number of RTX GPUs that Cycles can actively utilize with the OptiX backend? Does enabling more than two GPUs trigger a fallback to single‑GPU mode or produce memory allocation errors? Is the observed limitation documented as a known constraint, or should it be treated as a bug requiring a fix?