ChatGPT Voice Mode Runs on a 13-Month-Old Model

Developer Simon Willison (citing Andrej Karpathy) revealed that ChatGPT's voice mode runs on a GPT-4o-era model with an April 2024 knowledge cutoff — while the text interface uses GPT-5.5. That's a 13+ month capability gap for ChatGPT Pro subscribers paying $200/month, not prominently disclosed. OpenAI hasn't officially responded. The constraint is latency: frontier models can't yet run real-time voice cheaply. The competitive comparison: Google's Gemini Live voice mode uses Gemini 3.5 Flash (its latest model).

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Sources: Simon Willison's Blog · Build Fast with AI