ChatGPT
ChatGPT (Chat Generative Pre-trained Transformer) is a conversational artificial intelligence chatbot developed by OpenAI, launched on November 30, 2022[^c1]. Built on the GPT architecture and trained using reinforcement learning from human feedback (RLHF)[^c6], it generates human-like text responses across a wide range of tasks including writing, coding, translation, and analysis.
ChatGPT attracted one million registered users within five days of launch[^c2] and reached 100 million monthly active users within two months, making it the fastest-growing consumer application in history. Weekly active users grew from 300 million at the end of 2024 to 800 million by October 2025[^c16], and reached 900 million by February 2026[^c9][^c11]. The service had over 50 million paid subscribers[^c10] and held 79.98 percent of the generative AI chatbot market[^c12]. In the consumer AI app market, however, ChatGPT's share fell from 69.1 to 45.3 percent between January 2025 and January 2026, as competitors such as Google Gemini and Grok gained significant ground.[^c14]
The service is powered by a series of increasingly capable foundation models. The original release used GPT-3.5, a 175-billion-parameter model fine-tuned for conversation. GPT-4 followed in March 2023, introducing multimodal input and achieving performance in the top 10 percent of bar exam test takers[^c4]. Subsequent versions included GPT-4 Turbo, GPT-4o with native audio and vision, the o-series reasoning models (o1, o3), and GPT-5 in August 2025[^c5], which unified the GPT and o-series lines with native agentic capabilities. GPT-5.5 Instant, released in May 2026, reduced hallucination rates by 52.5 percent in high-sensitivity domains[^c13].
ChatGPT is offered through a freemium model with free basic access, a $20-per-month Plus tier, and a $200-per-month Pro tier. In 2026, OpenAI introduced advertising on the free and $8-per-month Go tiers as an additional revenue stream.[^c17] OpenAI generated $4.3 billion in revenue in the first half of 2025[^c7] but reported a net loss of $13.5 billion over the same period[^c8]. By early 2026, OpenAI's annualized revenue had grown further, though rival [[Anthropic]] surpassed it in April 2026.[^c15]
The platform has reshaped multiple industries and sparked widespread debate over AI safety, intellectual property, labor displacement, and ethical design. ChatGPT has been linked to lawsuits concerning mass shootings, teen suicide, accidental death, unauthorized legal practice, and copyright infringement. Its adoption has been associated with a decline in entry-level job openings and has accelerated discussions about the future of work, education, and human-AI interaction.