This work studies the problem of multi-period multi-sourcing supply planning with stochastic lead-times, quantity-dependent pricing, and delivery flexibility costs. We present a problem formulation that takes also into account holding and backlog costs and finite capacities of suppliers. The objective is to minimize the expected total cost while respecting suppliers’ capacity constraints and satisfying customer demand. In this paper, the proposed stochastic integer linear program is detailed and the first results of experiments are presented and discussed.