Windows XP is still copyrighted by Microsoft. Downloading it without a valid license is unless you own a legitimate retail or volume license key for XP x64 Edition. Archive.org hosts ISOs for preservation, but you still need your own product key.
Original MSDN file names & hashes for XP x64 SP2 (English): Windows Xp Professional X64 Edition Sp3 Download Iso
Many of the security and networking features introduced in the 32-bit SP2 and SP3 were already natively present in the initial or SP2 release of the x64 Edition because of its more advanced Server 2003 foundation. Microsoft Learn Service Pack 3 for XP Pro x64 - Microsoft Learn Windows XP is still copyrighted by Microsoft
Because it shared the Server 2003 kernel, it was incredibly stable. Many small business servers ran XP x64 as a workstation OS to run heavy SQL queries or CAD software. Original MSDN file names & hashes for XP