[en] The gas-cooled fast breeder reactor (GCFR) core development plan has been described as an incremental extension of the LMFBR program. The basis for this contention is reviewed along with some additional gas-cooled reactor precedence. Ideally, in the development of a reactor concept, it would be desirable to demonstrate the perforance of a full-sized fuel assembly under the anticipated irradiation and coolant conditions. Practically, however, this is seldom possible, particularly in fast reactors where fluence-to-burnup ratios increase with reactor power. Because of this limitation, the GCFR development program is based on qualifying the assemblies for the low distortions that occur during the swelling incubation period (approx. 50 MWd/kg). Extended burnup will be demonstrated in the operation of the GCFR demonstration plant core. The overall core development program and the related assumptions are discussed and the design goals stated. A multistage development approach is described and illustratd with an abbreviated program network. Major areas of the development program are briefly described