Gen 1: has bolt in type sensors (hex key)
Gen 2: has snap in type with retaining clips

They are not interchangeable.

That being said, I have a pair of gen 2 speed sensors for sale, I can't use them for my 2001.

Also, maybe it's a good idea to replace them in pairs, or at least use the same part from the same manufacturer because it may throw an abs code from mismatched sensors