The AGREE code solves the gas dynamics equation within a nuclear reactor core. Beginning in 2004, Volkan Seker began developing cylindrical porous medium support for the Pebble Bed Modular Reactor. This code was then applied to the SANA tests and PBMR-400 Benchmarks. The NRC then supported development of a hexagonal solver in anticipation of the General Atomic MHTGR license submission. AGREE will be used to model the HTTR transient reactor experiments. Further development included a Cartesian solver for gas flow around and through fuel blocks. More recent development has added support for complex control devices and other reactor features. In order to provide a neutronics solution, parts of the PARCS code are coupled to AGREE.