Compatibility of C applications with different versions of the CICS® Transaction Gateway API.
C client applications do not have to be recompiled to run with a newer version of CICS Transaction Gateway unless there is a specific requirement to do so for the version of the product you are upgrading from. For more information see Upgrading.
If you already have ECI V2 and ESI V2 applications deployed, and you upgrade your CICS Transaction Gateway to a later level, you can continue to use the existing version of ctgclient.dll on the remote machines or you can choose to upgrade it. You should consider the following points when choosing whether to upgrade ctgclient.dll on remote client machines: