PxrPathTracer and PxrUnified both support the risPathGuiding parameter.

When set to 1, this causes the incoming indirect radiance from all directions to be learned for a set of candidate points in the scene.

This information is used to determine the best directions in which to send indirect rays for efficient sampling of indirect lighting. These directions are combined with directions chosen by sampling Bxdfs (the default approach) using multiple-importance sampling to take advantage of the best of both techniques. RenderMan's implementation is highly optimized to incur only a minor overhead when enabled. It performs best for glossy and diffuse surfaces.


Below are two equal-time renders with risPathGuiding on and off.
Here the light is hidden from most of the scene by a sconce - a classic problem case for forward path tracers such as PxrPathTracer.  You can see that indirect guiding helps reduce the noise.