Right, the idea of the version token is to introduce it now, as early as possible, even if it is not needed, for prudence.
For example, if version 5 decides to change the semantics of some of the opcodes, we can then support both kinds, in the future.  Read old files _and_ the new ones.

Despite the fact that we claim that we don't guarantee interoperability, in reality it is very desirable.  During development, for instance. Frozen modules, .pyc files, and all that.