The River Transport Model, RTM, is part of the Community Earth System Model (CESM). It is managed by the Land Model Working Group (LMWG) as a part of CESM.
See the CESM web site for documentation and information:
IMPORTANT NOTE: RTM is only used for Paleo work -- use MOSART or mizuRoute otherwise
RTM is part of CESM3, but it's only supported use is for Paleo work, and other uses should use MOSART.
IMPORTANT NOTE: RTM's planned successor is mizuRoute
Longer term RTM will be removed in future versions of CESM and the new model mizuRoute will be used for Paleo work.