+** Guile now provide and uses an "effective" version number.
+
+Guile now provides scm_effective_version and effective-version
+functions which return the "effective" version number. This is just
+the normal full version string without the final micro-version number,
+so the current effective-version is "1.6". The effective version
+should remain unchanged during a stable series, and should be used for
+items like the versioned share directory name
+i.e. /usr/share/guile/1.6.
+
+Providing an unchanging version number during a stable release for
+things like the versioned share directory can be particularly
+important for Guile "add-on" packages, since it provides a directory
+that they can install to that won't be changed out from under them
+with each micro release during a stable series.
+
+** There are two new thread implementation options: "null" and "coop-pthreads".