Let F (x) be a diagonal integer-coefficient cubic form in m ∈ {4, 5, 6} variables. Excluding rational lines if m = 4, we bound the number of integral solutions x ∈ [−X, X] m to F (x) = 0 by O F, (X 3m/4−3/2+ ), conditionally on an "optimal large sieve inequality" (in a specific range of parameters) for "approximate Hasse-Weil L-functions" of smooth hyperplane sectionsWhen m is even, these results were previously established conditionally under Hooley's Hypothesis HW. Our 2 large sieve approach requires that certain bad factors be roughly 1 on average in 2 , while the ∞ Hypothesis HW approach only required the bound in 1 . Furthermore, the large sieve only accepts uniform vectors; yet our "initially given" vectors are only approximately uniform over c, due to variation in bad factors and in the archimedean component. Nonetheless, after some bookkeeping, partial summation, and Cauchy, the large sieve will still apply.