The brochure I saw said 1.0...course it also said it runs on Linux!!! Double-checked the Technicians Handbook, which SHOULD be right, and it says 4.0+. So I guess that should be trustworthy (maybe). Not a big deal to upgrade the 5000, and you'll get lots of new features too.
Also remember that you need to enable optional feature licenses System OAI Events and Third Party Call Control.