Working on a 424, customer wants to add a T1.
Manual states
"© PRI is available on DK424 Release 4.0 systems with RCTUBA3/BB4, C3/D4, and E3/F4
processors"
Software level in programming reads as RCA4X25.
My question is what level is this and will it support a T1 card? I looks like it might be release 4 but I cannot find anything that confirms this.
Thanks

It's release 4.0. For a PRI, it's suggested that you use 4.3 since it's more recent software.
For a T1 using an RDTU card, you should be fine with that software you have.

Phonemeister is right. You do have release 4. However, PRI was not super stable with anything but the last few revisions of 4.3 which you don't have. You will likely have some strange issues with a PRI on that release, like PRI resets and calls getting disconnected for no apparent reason.

Thanks for the info.
What would be required for me to upgrade to 4.3?
Is it a flash upgrade or will I need to swap out the Processor?
Preferably a way that doesn't end in me having to reprogram the entire system.
Thanks,

You would need to procure the upgrade firmware chips. The last version is Rel. 4.3 revision AW. Using 280admin you would backup the current database, replace the chips and the upload the database back to the processor.

Are you talking about a T1 with an RDTU or a PRI with a RPTU/BPTU? If it's an RDTU, you should be fine with the software you're on now.