Assuming nothing changes, 4096-bit RSA has around 160 bits of security, roughly equivalent to 320-bit elliptic curves. Depending on how Moore's law progresses

Assuming nothing changes, 4096-bit RSA has around 160 bits of security, roughly equivalent to 320-bit elliptic curves. Depending on how Moore's law progresses and our understanding of the Universe, you may never need to change (ignoring all other possible ways your key can be acquired).