Transactions as Experiments in Capacity-Constrained Matching Markets

Working paper, October 2026. Comments welcome: [email protected]. Orders routed through procurement systems and online platforms create records that influence later assignments when capacity is scarce. We study a two-period matching market with fixed demand and capacity, uncertain relationship surplus, and signal precision that rises with transaction volume. Under fixed capacities, posterior changes that are additive in buyer or supplier identity affect competitive prices without changing assignments. The value of an observation depends on its revision of comparisons between feasible allocations and on the response of future matching. Atomless traders take aggregate precision as given and omit this public benefit from current choices. Near the competitive allocation, the planner reroutes trade in the information-gradient direction after weighting by the inverse curvature of current matching. Per-unit transfers that remove buyer and supplier fixed effects from marginal information benefits implement an interior planner allocation. Across 1,080 generated sparse markets spanning circulant regular, switched regular, and irregular supports, routing by marginal assignment-variance reduction captures a median 91.1 percent of the maximum first-order information gain available for the same local current-surplus cost, compared with 71.0 percent for mutual information.