The original Pyrex code as of 2006-04 is licensed under the following license: "Copyright stuff: Pyrex is free of restrictions. You may use, redistribute, modify and distribute modified versions." ------------------ Cython, which derives from Pyrex, is licensed under the Apache 2.0 Software License. More precisely, all modifications and new code made to go from Pyrex to Cython are so licensed. See LICENSE.txt for more details. ------------------ The output of a Cython compilation is NOT considered a derivative work of Cython. Specifically, though the compilation process may embed snippets of varying lengths into the final output, these snippets, as embedded in the output, do not encumber the resulting output with any license restrictions.