I told Reid Bucholz had to be 5yrs, I thought all P extensions had to be 5yrs.... see below
Prospect Extension (went into effect after 2010 season)
Any player who is currently under a prospect contract may be signed to a regular contract extension (see below), but they may also be signed to a prospect extension. Such an extension must be a 5-year deal where the annual salary is X% of their market value. The resulting annual salary must be no less than $4m. No matter what the current prospect contract is, the prospect extension kicks in the following year at the rate based on when the contract is given.