Is Threefish the only cipher with 1024 bits of security? Threefish has up to a massive 1024 bits of security.  Is it the only cipher with such overkill security?
If we are talking about symmetric encryption, the PAGES block cipher based on Speck support key size 1024 bits and PAGES+/PAGES— variants support key sizes up to 2048 bits. However, I have not seen any independent cryptanalysis of these, so I can't recommend them. If we talk about the ciphers which have some cryptanalysis available, the Kalyna block cipher supports up to 512-bit keys.