Track an ordered eos_token_ids list (not just one id) and add is_eos(). gpt-oss/harmony ends the assistant turn on <|return|> and also treats <|call|> and <|endoftext|> as terminators (generation_config.json eos_token_id = [200002, 199999, 200012]); single-eos families are unchanged. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>