Outside of Rookie contracts, options only exist for the last year of NBA deals. A 4 year deal can only have an option in year 4.We've only seen something for 4 years and between 46 and 52. What is important too are what the years really are. Are they all guaranteed? Are there player or team options. I would think Smart would want 2 years locked and then an opt-out option to hit the market again.
That said, I wouldn't expect an option here. Ainge is paying a premium this year to lock in value in years 2-4. A 4/48 deal values Smart at $14M/year. A 4/51 deal values him at $15M/year. (These numbers are based on subtracting out the QO rate in year 1 because Smart has nowhere to get an offer from at this point so that's the baseline.) If you turn this into a 3+1 deal, the Celtics would be, essentially, paying $15M/year on the 4/48 deal, with downside risk or $16.5M/year at 4/51. Even as a big Smart booster, I don't think I could justify giving Smart that much money with a player option on the back end. (I think he's worth that much in the abstract, but you don't win championships by paying players what they are worth.)