Humans continuously adapt locomotor patterns. Whether energetic cost reduction is the primary objective or a by-product of locomotor adaptation is not known. If energetic cost is the primary objective, then manipulating energetic cost will affect the locomotor pattern. Our study aims to determine if information about task duration affects energetic cost and locomotor adaptation during split-belt walking. We hypothesize that information about a longer adaptation duration will result in lower metabolic costs and lower mechanical work. N=52 participants walked for 10 minutes with the belts moving at 1.5 and 0.5 m/s, followed by 6 minutes of walking with both belts at 1.0 m/s. Nineteen participants walked on the split-belt while we provided True information about time remaining every minute (Group T). Nineteen participants received False information that split-belt adaptation duration was around 30 minutes (Group F). Fourteen participants walked on a split-belt with accurate information about task duration, and one update at 5 minutes remaining (Group C). Participants in Groups C and F had a lower rate of change in metabolic cost from baseline (p=0.002) and generated less positive work (p=0.012) than individuals in Group T. Changes in positive work by the fast leg predicted metabolic cost reductions only in Group F (R=0.18, p=0.040). Participants in Group F showed greater split-belt aftereffects than the C and T groups (p<0.001). We conclude that walking biomechanics are adapted to support an energetic cost reduction when maintaining an energetic reserve is needed, as is the case for Group F, but not Group T.