Spot premium for opening long option token positions (buying long options):

$1 - (strikePrice * underlyingReserve / shortReserve)$

Spot premium for closing long option token positions (selling long options)

$1 - (underlyingReserve / (shortReserve * strikePrice))$

Where underlyingReserve and shortReserve correspond to the Uniswap Pair for the option.