With the ITER project entering the second half of the construction phase and various national and international plans for fusion prototype power plants being in early to advanced stages, fusion has entered the delivery era. With the urgency of the climate crisis being at the forefront of government policy agendas it is important to focus on the commercialisation of fusion power plants as the ultimate end goal of fusion research. This contribution will cover cost optimisation of fusion as well as optimisation of the value proposition that fusion can bring to target energy markets. In particular, it will focus on how both aspects are being considered for the STEP (Spherical Tokamak for Energy Production) prototype reactor to assure the STEP programme succeeds in its mission to “Deliver a UK prototype fusion energy plant, targeting 2040, and a path to commercial viability of fusion.”