Agreements reached at the Antarctic Treaty Consultative Meetings (ATCMs) are among the primary means for addressing Antarctic conservation and environmental protection issues. However, according to contemporary scholars, Antarctic Treaty decision-making is becoming increasingly unresponsive to the rising environmental challenges in the region. We assessed the performance of Antarctic Treaty decision-making by measuring the rate and diversity of decision-making over the last 6 decades. To measure the rate, we counted the number of inputs and outputs of ATCMs and calculated the time taken for legally binding outputs to enter into force. To measure diversity, we calculated the range of topics addressed by the inputs and outputs of ATCMs. The average number of agreements reached per ATCM increased from 1961 to 2022. Although the diversity of Antarctic topics discussed at ATCMs remained consistently high, the diversity of topics on which legally binding agreements were adopted declined significantly. Antarctic issues-including those of highest priority-are now almost entirely dealt with through nonbinding, soft-law agreements. It is plausible that this move away from binding decisions reflects a dynamic governance institution evolving to respond to new pressures. However, we suggest that the change reveals a concerning shift in decision-making behavior and performance, unique to the treaty's history. Soft law is beneficial in some cases, but its overuse diminishes accountability and transparency, significantly reducing the parties' abilities to understand and measure their performance, including the outcomes and impacts of decisions. Although the rate and diversity of ATCM inputs and outputs provide only a partial view of decision-making performance, the exploration of these metrics provides a foundation for asking essential questions about the impacts of Antarctic Treaty governance on the region's environmental protection and conservation.