Since x86-x64 has taken over the PC market share over 32-bit x86 processors as an OEM standard, It's unlikely what Instruction Set Extensions is exclusive to x86-x64, since nobody seems to know.
List of Instruction Set Extensions
MMX 1996 (both 32-bit and 64-bit)
3DNow! 1998 (once supported by AMD for both 32-bit and 64-bit but now deprecated)
SSE 1999 (both 32-bit and 64-bit)
SSE2 2001 (both 32-bit and 64-bit)
SSE3 2004 (both 32-bit and 64-bit)
SSSE3 2006 (both 32-bit and 64-bit)
SSE4 2006 (both 32-bit and 64-bit)
SSE5 2007 (development aborted 32-bit and 64-bit exclusivity unknown)
AVX 2008 (Exclusivity Unknown, Either 32-bit or 64-bit)
F16C 2009 (Exclusivity Unknown, Either 32-bit or 64-bit)
XOP 2009 (Exclusivity Unknown, Either 32-bit or 64-bit)
FMA/FMA4/FMA3 2011 & 2012 (Exclusivity Unknown, Either 32-bit or 64-bit)
AVX2 2013 (Exclusivity Unknown, Either 32-bit or 64-bit)
AVX-512 (Exclusivity Unknown, Either 32-bit or 64-bit)
If any moderator knows if any of these Instruction Set Extensions are exclusive to x86-x64 processors, let me know because 32-bit x86 processors are declining in market share as OEM standard.
