EAPI="5-progress" contains features of EAPI="5" and the following additional changes:
- Support for "." characters in package names.
- Support for "." characters in USE flags.
- Support for repository dependencies (::${repository_name}) in DEPEND, PDEPEND and RDEPEND and atoms passed to best_version() and has_version() functions.
- Automatic unpack dependencies (configurable in ${repository_path}/profiles/unpack_dependencies/${EAPI} files).
- globstar shell option enabled by default.
- REPOSITORY variable set in ebuild environment.
- Support for make.defaults, use.force, use.stable.force, use.mask, use.stable.mask, package.use, package.use.force, package.use.stable.force, package.use.mask and package.use.stable.mask in ${repository_path}/profiles.
- package.mask, use.force, use.stable.force, use.mask, use.stable.mask, package.use, package.use.force, package.use.stable.force, package.use.mask and package.use.stable.mask can be directories.
- New master_repositories(), repository_path(), available_eclasses(), eclass_path() and license_path() functions.
- New package_manager_build_user() and package_manager_build_group() functions.
- diropts(), docompress(), exeopts(), insopts(), keepdir(), libopts(), use(), use_enable(), use_with(), useq(), usev() and usex() are disallowed in global scope.
- dohtml by default additionally installs files with .ico, .svg, .xhtml and .xml extensions.
- Support for use.aliases and package.use.aliases in ${repository_path}/profiles.

(Package managers might provide these changes in other EAPIs.)

See also: http://people.apache.org/~Arfrever/EAPI_4-python_Specification