We prove an upper bound on the energy density of the dilute spin-1 2 Fermi gas capturing the leading correction to the kinetic energy 8πaρ ↑ ρ ↓ with an error of size smaller than aρ 2 (a 3 ρ) 1/3−ε for any ε > 0, where a denotes the scattering length of the interaction. The result is valid for a large class of interactions including interactions with a hard core. A central ingredient in the proof is a rigorous version of a fermionic cluster expansion adapted from the formal expansion of Gaudin, Gillespie and Ripka (Nucl. Phys. A, 176.2 (1971), pp. 237-260).