Humm...
"CGC: How does Softimage XSI 4.0 interact with current and future hardware? 64-bit?
Currently, SOFTIMAGE|XSI supports rendering in 64-bit, and can leverage things like AMD Opteron memory. As always, we work very closely with companies like AMD, Intel and IBM and many others to closely track what the industry needs are. Softimage XSI was designed with the future in mind with an open, flexible architecture. "