In Eurus Energy Holdings v. Spain, the claimant, a Japanese energy investor, brought a claim under the Energy Charter Treaty (ECT) against Spain for its comprehensive reform of the renewable energy sector. Eurus alleged that legislative changes between 2012 and 2014, which replaced a feed-in tariff (FiT) regime with a new system based on a 'reasonable rate of return', violated its rights under ECT Articles 10(1) (fair and equitable treatment) and 13 (expropriation) by drastically reducing revenues from its 21 wind farms. The tribunal, administered by ICSID, first issued a decision on jurisdiction and liability in March 2021. It declined jurisdiction over claims related to a 7% tax on electricity production, finding it a bona fide taxation measure carved out by ECT Article 21. However, it affirmed jurisdiction over the merits of the FET and expropriation claims, dismissing Spain's objections based on the CJEU's Achmea decision, holding it inapplicable to a dispute involving a non-EU investor under the multilateral ECT. On the merits, the tribunal dismissed the expropriation claim, finding that the claimant did not possess an 'acquired right' to an immutable subsidy regime under Spanish law. The decision rested on the fair and equitable treatment (FET) standard. The tribunal found that while Spain retained its regulatory power, any changes must be proportionate. It concluded that the claimant did not have a legitimate expectation that the specific FiT regime would continue indefinitely. Nevertheless, the tribunal found one specific element of the reforms breached the stability obligation inherent in the FET standard: a 'retro-active claw-back' mechanism. This feature calculated the new reasonable return by taking into account subsidies already lawfully paid, effectively penalizing the investor for past performance. The tribunal found this action to be a disproportionate impairment of the investment and ordered the parties to negotiate the quantum attributable solely to this breach. In a partial dissent, arbitrator Oscar Garibaldi disagreed with the dismissal of the remainder of the FET claim, arguing that the majority wrongly disregarded Spain's specific commitments and that the reforms as a whole constituted a radical change that frustrated the investor's reasonable expectations. Following the death of the tribunal's president, James Crawford, the tribunal was reconstituted with Anne K. Hoffmann as president. As the parties failed to agree on damages, the case entered a quantum phase. In its final Award of November 2022, the tribunal largely adopted the claimant's methodology, crucially selecting a later valuation date (June 2021) to ensure full reparation. It ordered Spain to pay Eurus €106.2 million in damages, plus interest, and approximately USD 4.3 million in costs. In September 2023, Spain applied to annul the Award and requested a stay of enforcement. An ad hoc Committee was constituted, comprising Bernard Hanotiau (President), Katherine González Arrocha, and Penelope J. Ridings. In a March 2024 decision, the Committee addressed the stay, rejecting Spain's request for an unconditional stay due to a "real risk" of non-compliance. Instead, it made the continuation of the stay conditional upon Spain posting appropriate security. After Spain failed to post the security as ordered in a subsequent April 2024 decision, the Committee, on 17 June 2024, lifted the stay of enforcement entirely. It concluded that Spain's non-compliance removed the justification for the stay, thereby permitting Eurus to pursue enforcement of the Award while the annulment application remains pending.