NOTICE DATE: December 12, 2025

NOTICE TYPE: M-A121225-01 Settlements

SHORT DESCRIPTION: Software Issue Identified Impacting Ancillary Service Trades

INTENDED AUDIENCE: All Market Participants

DAYS AFFECTED: December 5 -10, 2025

LONG DESCRIPTION:  ERCOT has identified a software issue impacting several areas. An issue in the market systems prevented certain Ancillary Service (AS) trades from being applied to a database table for downstream applications. This software issue was fixed in production systems at approximately 10:00 am on December 10, 2025.  This impacted the following areas:

• AS trades in Ancillary Service Imbalance Settlements and AS Trade Overage Settlement - The impacted records were not passed to Settlements to be included in the AS Imbalance Settlements or the AS Trade Overage Settlement. The Operating Days impacted are 12/5/2025 and 12/6/2025, as these Initial Settlement Statements have already been issued. ERCOT has been able to retrieve the missing records and will insert them into the Settlement System for evaluation of a Resettlement. If the Resettlement threshold is not met, settlement with the corrected records will be reflected on the Final Settlement Statements for the affected Operating Days.  For Operating Days 12/7/2025 through 12/10/2025, the missing records will be inserted in advance of Initial Settlement Statements being issued.
• Reliability Unit Commitment (RUC) Capacity Short Calculation - The missing records were not considered in the Market Management System (MMS) RUC Capacity Short optimization process. Capacity short calculations did not have accurate Ancillary Service Positions for all Qualified Scheduling Entities (QSEs) and may be incorrect. This issue was corrected on December 10, 2025, however, re-optimization and recalculation are still ongoing for Operating Day 12/8/2025 . This Operating Day is the only potentially impacted Operating Day for this issue as it was the only day for which RUC instructions were issued. If ERCOT cannot calculate the corrected data by Initial Settlement, the corrected data will be inserted into the Settlement System for evaluation of a Resettlement. If the Resettlement threshold is not met, settlement with the corrected records will be reflected on the Final Settlement Statements. A follow up Market Notice describing the resolution of this issue will be sent after resolution.
• Real-Time Ancillary Service Awards for Non-Controllable Load Resources - In affecting the Ancillary Service Positions for some QSEs, this issue also impacted the validation of self-provision of Ancillary Services for the Real-Time Market.  QSEs may not have been awarded in Real-Time for self-provided Ancillary Services if the validation used artificially low Ancillary Service Positions. This issue potentially impacted Operating Days 12/5/2025 through 12/10/2025.  Further analysis is being done to evaluate impacts and the potential need to correct prices.

ERCOT will be identifying a January 2026 stakeholder meeting at which to provide additional information and to allow time for questions.

CONTACT: If you have any questions, please contact your ERCOT Account Manager. You may also call the general ERCOT Client Services phone number at (512) 248-3900 or contact ERCOT Client Services via email at ClientServices@ercot.com.

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dg