TAPI version 1.3 (sometimes referred to as TAPI 1.03) was the first released version of the TAPI specification. The TAPI 1.3 system binaries (TAPI.DLL and others) are only found in the TAPI 1.0 SDK, which can only be found on the Microsoft® Developer Network (MSDN) Level II subscription. The system binaries (found in the REDIST directory) are redistributable but are designed only to run on Microsoft Windows® 3.1 and Windows® for Workgroups 3.11. They are not supported (and won't work) on any version of Microsoft Windows 95 or Microsoft Windows NT.
The headers and libraries that are used to develop a TAPI 1.3 application are only available in the TAPI 1.0 SDK and only support Win16 development. In fact, the TAPI 1.3 libraries are the only Win16 libraries available and must be used for all Win16 applications, regardless of the target platform or target version.
The TAPI 1.3 system binaries only support Win16, TAPI 1.3 TSPs, and applications.