<![CDATA[This study examines the adaptability of international arbitration in resolving cross-border investment disputes between Indonesia and Singapore, focusing on Investor–State Dispute Settlement (ISDS) and investment agreement design. Using a qualitative normative juridical approach with comparative analysis of treaties, arbitral awards, regulations, and academic literature, the study identifies contrasting policy orientations. Indonesia demonstrates institutional adaptability through BIT termination and renegotiation, selective application of Fair and Equitable Treatment (FET), and gradual integration of investor due diligence obligations to safeguard regulatory sovereignty. In contrast, Singapore reflects normative adaptability by consistently applying FET, recognizing implied consent, and aligning remedial practices—such as interest awards—with international standards. The findings reveal two distinct yet complementary models of legal adaptability in international investment arbitration. This study contributes by offering a comparative and integrative framework linking normative, institutional, and remedial dimensions, providing insights for balancing investor protection, legal certainty, and state regulatory space in ASEAN investment governance. Penelitian ini mengkaji adaptabilitas arbitrase internasional dalam penyelesaian sengketa investasi lintas batas antara Indonesia dan Singapura dengan fokus pada Investor–State Dispute Settlement (ISDS) dan desain perjanjian investasi. Penelitian menggunakan metode yuridis normatif dengan pendekatan kualitatif dan studi komparatif terhadap perjanjian investasi, putusan arbitrase, regulasi, dan literatur akademik. Hasil penelitian menunjukkan bahwa Indonesia menampilkan adaptabilitas institusional melalui pembatalan dan renegosiasi BIT, penerapan selektif prinsip Fair and Equitable Treatment (FET), serta integrasi bertahap kewajiban uji tuntas investor guna menjaga kedaulatan regulasi. Sebaliknya, Singapura menunjukkan adaptabilitas normatif melalui konsistensi penerapan FET, pengakuan implied consent, serta harmonisasi praktik remedial dengan standar internasional. Penelitian ini menegaskan adanya dua model adaptabilitas hukum yang berbeda namun saling melengkapi, serta menawarkan kerangka komparatif integratif yang menghubungkan dimensi normatif, institusional, dan remedial untuk menyeimbangkan perlindungan investor, kepastian hukum, dan ruang kebijakan negara.]]>
