OpenAI Agents SDK v0.16.1 Ships Breaking Change: Default Model Now GPT-5.4-mini Instead of GPT-4.1

GitHub·medium signal

Released May 7, the OpenAI Agents SDK v0.16.1 silently changes the default model from gpt-4.1 to gpt-5.4-mini, which affects any agent or run that doesn't explicitly set a model. Because GPT-5.4-mini is a GPT-5-class model, implicit defaults now include reasoning.effort='none' and verbosity='low' — potentially altering agent behavior for anyone upgrading without reading the changelog. Also adds max_turns=None option to disable the 10-turn default limit.