ChatGPT is OpenAI's flagship conversational AI assistant and the most widely used chatbot in the world, with several hundred million weekly active users. As of mid-2026 it runs on the GPT-5.5/5.6 model family (Instant for fast everyday answers, Thinking/Sol for deeper reasoning, and Pro for maximum compute on hard problems). The product has expanded well past simple chat: it now includes Deep Research (multi-step web investigations), Agent Mode/Operator for autonomous multi-step tasks (booking, browsing, ordering), Codex for agentic coding, Sora for video, native image generation, custom GPTs, and a growing shopping/commerce layer with product recommendations. Pricing spans six tiers: Free (ad-supported in the US, limited GPT-5.3/mini access), Go ($8/mo), Plus ($20/mo — the mainstream sweet spot), Pro ($100 and $200/mo tiers with 5x–20x usage and the full model family), Business ($20–25/seat), and Enterprise (custom). OpenAI has also begun showing ads on Free and Go tiers.