To solve the equation \( 1,000.66 + s = 1,000.66 \), we can use the property of addition that states that adding zero to a number does not change its value.
So, if we want to isolate \( s \), we can subtract \( 1,000.66 \) from both sides of the equation:
\[ s = 1,000.66 - 1,000.66 \]
Now, performing the subtraction:
\[ s = 0 \]
Thus, the value of \( s \) that makes the addition sentence true is
\[ \boxed{0} \]