Neutron scattering is used to probe magnetic interactions as superconductivity develops in optimally doped Fe 1+δ Se x Te 1−x. Applying the first moment sum rule to comprehensive neutron scattering data, we extract the change in magnetic exchange energy [J R−R S R · S R ] in the superconducting state referenced to the normal state. Oscillatory changes are observed for Fe-Fe displacements |R| < ξ, where ξ = 1.3(1) nm is the superconducting coherence length. Dominated by a large reduction in the second nearest neighbor exchange energy [−1.2(2) meV/Fe], the overall reduction in magnetic interaction energy is H mag = −0.31(9) meV/Fe. Comparison to the superconducting condensation energy E SC = −0.013(1) meV/Fe, which we extract from specific heat data, suggests the modified magnetism we probe drives superconductivity in Fe 1+δ Se x Te 1−x .