Methods and systems are described herein for extending configuration dependent extensible software programs. Classes of a core extensible software program may be extended by adding a configuration dependent extension. The extensions may be added statically prior to compiling the core version of a software program or dynamically at runtime. The declaration of extensible core classes may include an extensibility attribute with an indication of whether the class is statically extensible or dynamically extensible. An object description language is also described herein for appropriately declaring configuration dependent extensible classes. Also, a pre-processor is described herein for processing the object description language to generate a source code representation of the extensible class declarations and their extensions. The source code representation may then be used to generate the extended version of the core software program.