The Classic, LX and the single processor models of the SS20 are still supported under some version of SunOS 4.1.x. A lot of people wanted these machines but only if they ran SunOS 4.1.x. When the Classic/LX came out, clone manufacturers were able to provide SunOS 4.1.x with it, Sun came out with SunOS 4.1.3C some time later.
The Classic, LX, SS4, SS5 and SS20 are supported in the most recent Solaris 1.x release, SunOS 4.1.4 (Solaris 1.1.2). The Classic and LX are supported since 4.1.3C (release for LX & Classic only), the SS20/SS5 since release 4.1.3_U1 rev B (Solaris 1.1.1B). The SS4 and SS20 with HyperSPARC since 4.1.4. Note that none of these OS versions support SuperSPARC MP or any of the new graphics hardware (ZX, TZX, SX, S24). The TCX adapter is only supported as a cgthree, and SunOS 4.x doesn't use all its acceleration features.
The Voyager is not supported under SunOS 4.1.x, too many new device drivers have been added plus the suspend resume feature.
The XDbus machines SS1000/SC2000 are also not supported under SunOS 4.1.x. Support for their kernel architecture and XDBus is missing in 4.x.
The UltraSPARC based machines are not supported under SunOS 4.1.x. The new supervisor mode instructions, the new MMU, buses and devices are not supported under 4.1.x.
Sun acquired the Business Systems Division of Cray Research and now supports the Cray CS6400, a 64 SuperSPARC machine that runs a modified version of Solaris 2.x, known as "Cray Solaris".
The largest Solaris 2.x machine you can currently buy from Sun is the Sun Enterprise 10000, a machine that supports upto 64 UltraSPARC cpus, 64 I/O channels and 64 GB of memory at the same time.
Fujitsu sells an even larger machine, the AP-3000, a system with upto 2048 UltraSPARC cpus @300MHz.