Hi, During some testing of boost::serialization features, I tried to do this : Let's say we have a class X, the current version for this class is 5 (BOOST_CLASS_VERSION(X, 5)). Serialize in class X is split into save/load.What I'd like to do now, is save an object of type X at version 3 to make the object loadable by an older version of my software. that is get ""<X class_id="0" tracking_level="0" version="3">" in my resulting file instead of "<X class_id="0" tracking_level="0" version="5">". I've gone through the documentation of boost::serialization and I found only one thing. A TODO speaking about "Back versionning". It's not clear for me if this part speaks about the archive (like xml_oarchive, xml_iarchive, ...) or the object I can serialize, in other words does it concern this line "<boost_serialization signature="serialization::archive" version="5">" or a line like this one "<test class_id="0" tracking_level="0" version="2">" in a resulting file ? Maybe it concerns both but that I don't know. So apparently If I understand the documentation correctly I can't do what I describe above at the moment. Does anyone know if it's going to be implemented soon, or if I can be of any help ? Vincent