Hello RossPickle,
I can't find any article regarding TAPI end of support. But Latest versions were developed for Windows XP and compatibility system updates were released in Windows 8 and Windows 10 OS. However, it doesn't seem that Microsoft is anymore maintaining the development of TAPI since after version 1903 there are still many reported bugs and issues that haven't been addressed.
My recommendation looking into the future for telephony would be CSTA3, but always check if your vendor works with that standard too.
Hope this helps with your query,
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