Many WTO members are actively negotiating new rules to enhance the sustainability of their commitments within the organisation. These negotiations are pivotal in driving the constitutionalisation of the WTO and reforming its rules. Given the stagnation of multilateral negotiations, WTO members are engaging in plurilateral negotiations to advance these rules. I categorise these negotiations into three main areas: liberalising international trade, advancing social rights, and committing to environmental sustainability. This chapter examines the progress and outcomes of these negotiations to determine which TSDCs are being incorporated into WTO law and whether they are adequate to establish a legal basis for the sustainability test.