Upgrade B2B Server from 4.0 to 4.6?

Can anyone shed some light on how seamless the upgrade is from 4.0 to 4.6? Specifically I’m trying to guage what the potential impact may be to any of my flows developed on 4.0.

Thanks in advance!

Ostensibly, your flows shouldn’t require any changes. The Release notes for 4.6 will provide information about changes between 4 and 4.6. The best proof, however, is to move your packages to a test/dev 4.6 environment and see what happens.