I believe x86 is standing for the architecture, since AMD usually fully compatible to Intel except for the newest Intel command sets, it must be compatible to AMD, because a 586er Intel chip as example has no known commands to me, that wouldnt be supported by todays AMD prozessors. For the windows version, I can garantue compatiblity to Athlon XP "Barton".
If you are still worried... get the source code and compile it for AMD-64

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PS: PuTTY is easy to compile on win32 system, works without a single hassle using MSYS/MinGW