A Nous 404 answering "This model is no longer free. To continue using the paid variant, switch to '<slug>'." fell through _404_RULES to _V_UNKNOWN, so the retry loop kept retrying a slug that can never succeed again. The route retirement is a model-lifecycle change, not a missing model body or an account balance problem, so it now maps to model_not_found: non-retryable, fallback armed (#123180).