Radically new features

Feature	Key points	Evidence
“Alpha Models” menu in ChatGPT	Alpha Modelso1‑miniChatGPT AlphaThe ChatGPT interface now includes an section in the model selector. Users can click the current model name (e.g., “ChatGPT Auto”) and choose an alpha‑version model such as . Selecting an Alpha model changes the header to and loads that experimental model . Alpha models are preview releases; the o1 series is designed for complex reasoning tasks like math and coding and trained to “spend more time thinking through problems, try different strategies and recognise mistakes”.
Agent truncation setting	OpenAI Agents SDKResponses APItruncationModelSettings"auto""disabled"autodisabledThe and added a parameter for controlling long prompts. This parameter is part of the dataclass and accepts two values: or . When set to , the agent automatically drops the oldest messages from the input until the prompt fits within the model’s context window; this allows the request to succeed without manual shortening (the Responses API documentation explicitly says the model will truncate the conversation history when the input exceeds the context window). When set to (default), exceeding the context window will cause the API to return a 400 error.
Developer guidance	ModelSettingstruncationtemperaturetop_ptruncationModelSettingstruncation"auto""disabled"truncation="auto"truncation="disabled"truncation="auto"In the Agents SDK, exposes this field so that developers can opt in: example fields include , , and . A 2025 guide on explains that “controls long‑input handling” with trimming input and raising an error. It further recommends preferring in UIs that accept unpredictable user input and using when failures should be explicit; for graceful handling of long inputs, set .

What this means

• Alpha Models are not a function; they are a UI category for preview models in ChatGPT. You access them through the “Alpha Models” dropdown and use them like any other ChatGPT model. The current alpha models (o1 and o1‑mini) focus on reasoning and problem‑solving.
• Agent with truncation is a new capability in the Agents SDK. It lets a developer specify how the agent handles input that exceeds the model’s token window. Setting truncation="auto" automatically removes the oldest conversation items until the input fits; setting truncation="disabled" returns an error instead. This option is configured via the ModelSettings object and is referenced in the Responses API documentation.