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I understand that you are encountering an issue, if it has been executed using threads with the REST API or SDK v1, it can be cancelled. Else, it can be deleted using either the REST API or Python SDK v1.
Kindly refer below documentation: https://learn.microsoft.com/en-us/azure/ai-services/openai/assistants-reference-runs?tabs=python#cancel-a-run
Please create a support ticket if above methods does not work as it might be a server-side issue too.
Thank You.