This paper examines how institutional change within UN cyber diplomacy has reshaped participation, coalition behaviour, and normative contestation over time. Rather than treating current fragmentation as a sudden rupture, it traces how diplomatic practices evolved from the late Group of Govermental Experts (GGE) period through the institutionalisation of the Open-Ended Working Group (OEWG), including the 2021-2025 cybcle and its transition toward the UN Global Mechanism on ICT security. The Paper asks how changes in institutional design and participation have altered the politics of cyber norm negotiation. While the OEWG broadened access and strengthened the legitimacy of UN cyber discussions, it has also made visible deeper disagreements over sovereignty, responsible state behaviour, capacity building, and institutional dialogue, and the future architecture of cyber governance. Drawing on process tracing and institutional analysis, the paper analyses official reports, state statements, working papers, UNWebTV transcripts, to identify patterns in diplomatic behaviour across successive UN cyber processes. Particular attention is given to how expanded participation, procedural debates and coalition positioning have shaped the movement from consensus-building towards more explicit forms of contestation. The paper contributes to debates on interdependence, alignment, and alliances by showing how cyber governance fragmentation is not only shaped by geopolitics, but also by institutional evolution and contested efforts to define the post-OEWG order. 

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