NEC4 ECC Contractors savings for Option A

Option A (Contractor design). If the Contractor proposes a cheaper type of piling than initially proposed in his tender, are the Prices reduced in the Activity Schedule providing the savings for the Client only? Note that the alternative pricing solution fully complies with the Client’s Scope.
I would assume that the Contractor needs to resubmit his proposal for acceptance under 21.2?
And clause 16.1 does not apply in this case as the would not be a change to the Clients Scope?

If it is Contractor design and the design is compliant then the Prices are not reduced. The matter is not a compensation event, see the second bullet point of clause 60.1 (1).

You are right, clause 16.1 only applies if the request involves a change to the Client’s Scope and yes the design would need the Scope requires.