No, in section 3.4.1.1 General-Purpose Registers in 64-Bit Mode of the Intel® 64 and IA-32 Architectures Software Developer’s Manual, it says, "32-bit operands generate a 32-bit result, zero-extended to a 64-bit result in the destination general-purpose register."

`xor eax, eax` actually generates 0x31 0xc0, and `xor rax, rax` generates 0x48 0x31 0xc0. 0x90 decodes to xchg eax, eax in all modes except long mode, which has no effect. In long mode, the opcode 0x90 has no effect still but is no longer equal to xchg eax, eax.