This article examines how fragmentation of the global trade regime into preferential agreements, built on a multilateral baseline of World Trade Organization (WTO) rules, affects trade governance. The analysis relies on 105 interviews with trade policy professionals in core WTO members and a conceptual distinction between ‘thick’ and ‘thin’ institutionalism to capture institutional changes in the global trade governance architecture. The WTO's thick institutionalism facilitates institutionalized interactions among members of the trade policy community that are essential for transparency and dialogue and the rule of law character of the trade regime. It secures the continued belief of trade policy professionals in the WTO's centrality in trade governance. The thin institutionalism of the network of preferential agreements spells the return to à la carte forms of trade governance and benefits those with the technical and political capacity to successfully navigate the fragmented governance architecture. Ongoing institutional transformations shift global trade governance away from rules-based back to more power-based forms.