/usr/include/ql/experimental/credit/ is in libquantlib0-dev 1.4-2+b1.
This file is owned by root:root, with mode 0o755.
..
/usr/include/ql/experimental/credit/all.hpp
/usr/include/ql/experimental/credit/basket.hpp
/usr/include/ql/experimental/credit/blackcdsoptionengine.hpp
/usr/include/ql/experimental/credit/cdo.hpp
/usr/include/ql/experimental/credit/cdsoption.hpp
/usr/include/ql/experimental/credit/defaultevent.hpp
/usr/include/ql/experimental/credit/defaultprobabilitykey.hpp
/usr/include/ql/experimental/credit/defaulttype.hpp
/usr/include/ql/experimental/credit/distribution.hpp
/usr/include/ql/experimental/credit/factorspreadedhazardratecurve.hpp
/usr/include/ql/experimental/credit/issuer.hpp
/usr/include/ql/experimental/credit/loss.hpp
/usr/include/ql/experimental/credit/lossdistribution.hpp
/usr/include/ql/experimental/credit/nthtodefault.hpp
/usr/include/ql/experimental/credit/onefactorcopula.hpp
/usr/include/ql/experimental/credit/onefactorgaussiancopula.hpp
/usr/include/ql/experimental/credit/onefactorstudentcopula.hpp
/usr/include/ql/experimental/credit/pool.hpp
/usr/include/ql/experimental/credit/randomdefaultmodel.hpp
/usr/include/ql/experimental/credit/recoveryratemodel.hpp
/usr/include/ql/experimental/credit/recoveryratequote.hpp
/usr/include/ql/experimental/credit/recursivecdoengine.hpp
/usr/include/ql/experimental/credit/riskyassetswap.hpp
/usr/include/ql/experimental/credit/riskyassetswapoption.hpp
/usr/include/ql/experimental/credit/riskybond.hpp
/usr/include/ql/experimental/credit/spreadedhazardratecurve.hpp
/usr/include/ql/experimental/credit/syntheticcdo.hpp
/usr/include/ql/experimental/credit/syntheticcdoengines.hpp