MISO’s Independent Market Monitor said the recently uncovered, eight-year-old repeat error in the RTO’s capacity market that caused a $280 million impact in this year’s auction alone is unfortunate but insisted the resulting prices were efficient.

MISO said a yearslong software error caused it to clear more capacity than intended in past capacity auctions and which has resulted in an approximate $280 million impact to market participants in this year’s auction.

MISO members largely agreed that MISO’s new capacity auction structure — featuring individual seasonal auctions and a sloped demand curve — is better for the health of the system.

Vistra has agreed to pay $38 million to wind down a long-running FERC inquiry into whether it manipulated prices in MISO’s 2015/16 capacity auction.

MISO said it no longer will recognize energy efficiency as a capacity resource beginning with the 2026/27 auction.

MISO said starting with the 2026/27 planning year, it will require its demand response resources to demonstrate actual demand reductions through tests to weed out imposters in the capacity market.

MISO’s 2025/26 capacity auction returned $666.50/MW-day prices across all zones in the summer, reinforcing the need for members to build new generation fast, the grid operator said.

Voltus filed a complaint with FERC against MISO, alleging the RTO’s “11th-hour” changes in testing and contract proof requirements ahead of the spring capacity auctions will harm demand response resources and affect rates.

MISO revealed it will crack down on demand response testing requirements ahead of its spring capacity auction, while some stakeholders argued the stepped-up measures amount to a change that requires FERC approval.