I think it is only required for group, or camp in BA campground

https://www.rimtorim.org/hike-it/

* You need a permit, which is where lottery drawing comes in, if you’re going to camp overnight in the Canyon.  

 

https://www.nps.gov/grca/learn/news/interim-permits-r2r.htm

The National Park Service (NPS) will begin issuing Special Use Permits on an interim basis for organized, non-commercial rim-to-rim and extended day hiking and running in the inner canyon of Grand Canyon National Park.

.....

Organized groups, including non-profits, conducting rim-to-rim and extended hiking and running will be required to obtain a Special Use Permit. Information about Special Use Permits for these activities, including permit applications and fees can be found on Grand Canyon National Park's website at http://www.nps.gov/grca/parkmgmt/sup.htm. Generally, any group, regardless of size, which has advertised to the general public, required individuals to sign up prior to participation, or that has an organizer who has been compensated for their services, including subsidized participation, will be required to obtain a Special Use Permit.