The Microsoft OS/2 SDK includes pre-release builds of OS/2, beta development tools, sample code, and loads of documentation. These were released prior to the OS/2 1.0 and 1.1 releases. Microsoft charged $3,000 in 1987 for the SDK. It was criticized as overpriced, buggy, and slow.
These were superseded by the smaller and less expensive Microsoft OS/2 Programmer's Toolkit
Much more information can be found here: OS/2 Museum, OS/2 Beginnings
November 1988 - SDK 1.06
The OS/2 SDK version 1.06 was somewhat unusual. It included the final version of IBM OS/2 1.1 SE and a pre-release of Microsoft's development tools and sample programs. Similar to the situation with OS/2 1.0, IBM released the new OS/2 version several months before Microsoft delivered the final development kits, and also several months before OEM versions of Microsoft OS/2 would appear. The 1.06 SDK underscored that Microsoft and IBM releases of OS/2 were identical as far as applications were concerned.
Wanted: Microsoft OS/2 SDK 1.06 November 1988 disk dumps