Under the ECC Option B is a compensation event subject to remeasure or is it a lump sum price?
It depends on the circumstances: see option B clauses 63.13 under NEC3 and 63.15 under NEC4.
Either way, unless the Project Manager and Contractor agree otherwise, the default method of working out the change in Defined Cost + Fee is under clause 63.1. If they agree otherwise, they can use rates and lump sums instead - see end of clause 63.13 under NEC3 and 63.2 under NEC4.
Thanks Jon. My understanding was as per your comment re 63.1 and 63.13. The Defined Cost + Fee then becomes the PWDD. I was just unsure if you were to agree to use rates whether these would be remeasured or not