If you’re upgrading from an ecobee3 to an ecobee4, you’ll need to feed the R/Rc/Rh wire into the Rc terminal.
If you’re already using a Power Extender Kit (PEK) with the ecobee3, you’ll need to do some re-wiring at the ecobee4. The R wire will go into the Rc terminal, the G wire into the C terminal, and the Y wire into the PEK terminal on the ecobee4. Remaining wires will go into the respective terminals.
The ecobee4 uses the same PEK as the ecobee3 lite. So if you're moving from ecobee3 lite to ecobee4 and are using the PEK, then you'll just wire it the same, the R to Rc, the G wire to C and the Y wire to PEK.