This concluding chapter analyzes the evolving relationship between the Asian Infrastructure Investment Bank (AIIB) and the Asian Development Bank (ADB) and assesses their roles in ASEAN development finance since 2016. Empirical evaluation and cross-correlation statistical analysis reveal that the AIIB and ADB do not operate as direct competitors but rather as complementary institutions, with the AIIB playing a secondary role in regions where the ADB is already established. The chapter refutes the notion of a hegemonic shift and proposes a constructivist framework to explain their interaction. The AIIB and ADB co-exist within a pluralistic development finance structure, characterized by functional differentiation, mutual embeddedness, and gradual normative adjustments. This chapter emphasizes that the relationship between these institutions fosters diversified sources of financing, thereby strengthening the policy space and strategic autonomy of ASEAN countries rather than triggering institutional replacement. The findings have important implications for understanding global development finance dynamics and offer insights into the evolving nature of international institutional cooperation.