originally, TWS 3.0 was supposed to be phased out by March 1. However, until all of the features of 3.0 are incorporated into the java version it should be supported. The main issue that I know about is the deep book on futures. There are a couple of other behind the scene issues related to institutional accounts. Wish I could give you a more explicit answer. If there are features of 3.0 that you believe are missing from 4.0 which you feel are essential, please send an e-mail to the management from the link on the ib web site.