The CDC classifies the countries according to the World Bank Database https://data.worldbank.org/indicator/NY.GNP.PCAP.CD?locations=MD&most_recent_value_desc=false (most recent year 2018).
The World Bank categorizes countries as follows:
Priority 1 (Low income by WB definition) - GNI per capita in USD below 1025
Priority 2 (Lower middle income by WB definition) - GNI per capita in USD 1026-3995
Priority 3 (Upper middle income A) - GNI per capita in USD 3996-6785
Priority 4 (Upper middle income B) - GNI per capita in USD 6786-9575
Priority 5 (Upper middle income C) - GNI per capita in USD 9576-12375
The CDC divides Developing Countries into 5 groups as the previous list was divided (to avoid any confusion in some existing regulations).
For a list of Developing Countries divided by categories please click the link.
All countries classified as "DEVELOPING COUNTRIES" (based on the GNI from 2018) can be found - listed alphabetically - below