To solve for \( ? \) in the equation \( x^{-3} = \frac{1}{x^?} \), we can manipulate the left side of the equation.
We know that \( x^{-3} \) can be rewritten as \( \frac{1}{x^3} \). Therefore, we have:
\[ x^{-3} = \frac{1}{x^3} \]
Now, we can set the right side of the original equation equal to this expression:
\[ \frac{1}{x^?} = \frac{1}{x^3} \]
Since both sides have the same form, we can equate the exponents:
\[ ? = 3 \]
Thus, the value of \( ? \) is:
\[ \boxed{3} \]