As per Cisco SDN's roadmap, APIC 4.0 was supposed to be released by August last week. However, this was not released yet.
We have plans to upgrade to 4.0 from 3.1(1i). if someone already have any updates on APIC 4.0 firmware (14.X for Fabric devices), could you help me if the direct upgrade was possible from 3.1 to 4.0 and when Cisco would be confirming on APIC 4.0
Release dates are ALWAYS tentative. We don't typically post a month or date to which releases are pending. We might advise a Quarter time frame, but again, these are all subject to change.
Compatibility is still being finalized. We should know in the next week or so which paths will be supported. I'll update this thread once confirmed.
Supported Upgrade Paths for Cisco APIC and the Switch Software