Thailand was initially cautious with its bilateral investment treaties (BITs), consistently eschewing investor-state dispute settlement (ISDS). From 1989 it began agreeing to ISDS, but only if both states were party to the Convention on the Settlement of Investment Disputes Between States and Nationals of Other States, which Thailand signed in 1965 but never ratified. From 1993, BITs increasingly provided for ad hoc arbitration. Major disputes emerged from the 1990s instead under contracts with foreign investors containing arbitration clauses. From 2004 concession contracts required Cabinet pre-approval. This limitation was extended to all public contracts from 2009, after the first treaty-based ISDS award against Thailand, although two further claims have been filed recently. A 2002 Model bit was revised in 2013 to incorporate more pro-host-state provisions, but Thailand had net foreign direct investment (FDI) outflows in 2011 and still concludes treaties with ISDS. These patterns suggest ‘more than bounded’ rationality.