USDC and USDT are the dominant stablecoins pegged to \$1 with a total market capitalization of over \$300B and rising. Stablecoins make dollar value globally accessible with secure transfer and settlement. Yet in practice, these stablecoins experience periods of stress and de-pegging from their \$1 target, posing significant systemic risks. The behavior of market participants during these stress events and the collective actions that either restore or break the peg are not well understood. This paper addresses the question: who restores the peg? We develop a dynamic, agent-based mean-field game framework for fiat-collateralized stablecoins, in which a large population of arbitrageurs and retail traders strategically interacts across explicit primary (mint/redeem) and secondary (exchange) markets during a de-peg episode. The key advantage of this equilibrium formulation is that it endogenously maps market frictions into a market-clearing price path and implied net order flows, allowing us to attribute peg-reverting pressure by channel and to stress-test when a given mechanism becomes insufficient for recovery. Using three historical de-peg events, we show that the calibrated equilibrium reproduces observed recovery half-lives and yields an order flow decomposition in which system-wide stress is predominantly stabilized by primary-market arbitrage, whereas episodes with impaired primary redemption require a joint recovery via both primary and secondary markets. Finally, a quantitative sensitivity analysis of primary-rail frictions identifies a non-linear breakdown threshold. Beyond this point, secondary-market liquidity acts mainly as a second-order amplifier around this primary-market bottleneck.

翻译：USDC与USDT是锚定1美元的主导稳定币，总市值已突破3000亿美元且持续增长。稳定币通过安全的转移与结算机制使美元价值在全球范围内可及。然而实践中，这些稳定币会经历压力时期并偏离1美元锚定目标，构成重大系统性风险。市场参与者在压力事件期间的行为，以及集体行动如何恢复或破坏锚定的机制尚未得到充分理解。本文旨在回答：谁来恢复锚定？我们为法币抵押型稳定币建立了一个基于智能体的动态平均场博弈框架，其中大量套利者与零售交易者在脱锚事件期间，通过显式的初级市场（铸造/赎回）与二级市场（交易所）进行策略互动。该均衡模型的关键优势在于：内生地将市场摩擦映射至市场出清价格路径与隐含净订单流，使我们能按渠道归因锚定恢复压力，并压力测试特定机制何时不足以实现恢复。通过对三个历史脱锚事件的校准，我们证明该均衡模型能复现观测到的恢复半衰期，并生成订单流分解：系统性压力主要依靠初级市场套利实现稳定，而当初级赎回功能受损时，需通过初级与二级市场协同恢复。最后，对初级通道摩擦的定量敏感性分析揭示了一个非线性崩溃阈值，超过该阈值后，二级市场流动性主要作为初级市场瓶颈周围的二阶放大器发挥作用。