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][^c34], though the company missed an internal goal of 1 billion weekly active users by end of 2025.[^c37] The growth rate showed marked deceleration: WAU stood at 800 million in December 2025, reaching 900 million only by February 2026.[^c41] By February 2026, the service had over 50 million paid subscribers[^c29] 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] In the European Union, ChatGPT reported 120.4 million average monthly users by October 2025.[^c33]
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 annualized run-rate revenue in April 2026.[^c15] Enterprise revenue accounted for 40 percent of OpenAI's total revenue, with strongest adoption in professional services, finance, and technology, which saw 11-fold growth year over year.[^c30][^c38] Enterprise retention was 88 percent at one year.[^c43] OpenAI CFO Sarah Friar privately suggested a delay of an initial public offering to 2027 over financial reporting readiness concerns, while CEO Sam Altman pushed for a Q4 2026 timeline.[^c42]
In April 2026, OpenAI launched Workspace Agents, a persistent cloud-based agent capability inside ChatGPT powered by Codex, described as an evolution of GPTs that can perform multi-step automation, run on schedules, and integrate with connected apps including Slack, Google Drive, and Salesforce.[^c31] On May 11, the company launched DeployCo (the OpenAI Deployment Company), a majority-owned subsidiary capitalized with over $4 billion to provide enterprise AI deployment services through on-site Forward Deployed Engineers.[^c32]
In May 2026, the company released GPT-5.5 Instant as the default ChatGPT model, launched a personal finance feature for Pro subscribers in the United States,[^c18] added spreadsheet integrations and a Trusted Contact safety feature, expanded its advertising business, entered a legal dispute with Apple over the ChatGPT-Siri integration, and released a beta ChatGPT add-in for Microsoft PowerPoint.[^c19] On May 29, ChatGPT suffered a major global outage with over 4,300 users in the US reporting problems on Downdetector; OpenAI acknowledged the issue and implemented mitigation measures.[^c20][^c21] Also in May, code found in the ChatGPT Android app version 1.2026.146 indicated upcoming features including a Find in chat search option, a Plugins section for organizing tools, and multi-file selection in the ChatGPT Library.[^c22][^c23]
In early June 2026, Florida became the first US state to sue OpenAI, alleging that ChatGPT assisted mass shooters, encouraged suicide, and addicted minors.[^c24] Canadian privacy regulators also issued findings that ChatGPT's training practices violated Canadian privacy laws, stating that OpenAI "launched ChatGPT without having fully addressed known privacy issues."[^c25] Developers discovered traces of an unannounced GPT-5.6 model with a 1.5 million token context window in OpenAI's Codex backend logs,[^c26] and OpenAI announced full Codex integration into ChatGPT at its "Intelligence at Work" event.[^c27][^c36] Codex had reached 5 million weekly active users — six times its February 2026 level — with 20 percent of users being non-programmers.[^c35] Reports indicated OpenAI was preparing the biggest ChatGPT overhaul since launch, transforming it into a superapp by integrating coding tools, AI agents, and partner services.[^c28]
The platform has reshaped multiple industries and sparked widespread debate over AI safety, intellectual property, labor displacement, and ethical design. In October 2025, OpenAI disclosed that approximately 1.2 million weekly users — 0.15 percent of the 800 million weekly active user base — send messages containing indicators of suicidal planning or intent, with an additional 560,000 users (0.07 percent) showing signs of psychosis or mania.[^c39][^c40] 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.