According to Sensor Tower data, ChatGPT, an OpenAI product, surpassed 1 billion monthly active users worldwide in May, becoming the fastest application to reach this milestone speed ever. The report said that among ChatGPT users who installed Anthropic Claude in the United States in Q1 2026, time spent on ChatGPT was 5% lower one month later than the average over the previous eight months.
ChatGPT’s growth trajectory: from saturation warnings to 1 billion users
From August to November 2025, ChatGPT monthly active users grew by 6%, from about 810 million to around 810 million. The slowing growth rate prompted OpenAI CEO Sam Altman to issue an internal “red alert” memo, calling for improvements to personalization, reliability, and image generation features.
Over the next roughly six months, monthly active users increased by about 190 million, reaching 1 billion in May 2026. Sensor Tower’s report noted that users who installed Claude did not leave ChatGPT, but instead split their usage time between the two platforms.
Claude status: 56 million monthly active users, 640% YoY growth, Opus 4.8 released
As of Q2 2026, Claude’s global monthly active users were 56 million, with Claude’s monthly active user year-over-year growth at 640%, while ChatGPT for the same period was 62%. Last week, Anthropic released Claude Opus 4.8. In an official statement, Anthropic said that Opus 4.8 performed better than GPT-5.5 in at least 12 benchmark tests, covering knowledge work, agent tool usage, and long-context tasks. Anthropic’s official statement also said that Mythos-class models will be opened to all customers within the next few weeks, though the exact date has not been announced.
Anthropic and OpenAI IPO status
Anthropic: Secretly filed an IPO application with the U.S. SEC on June 1, 2026
OpenAI: Reuters reported that it plans to submit confidential draft registration statements to Goldman Sachs and Morgan Stanley within the next few weeks, targeting a listing later in 2026
Polymarket market data (as of the time of writing): Traders assign a 74% probability that Anthropic completes its IPO before OpenAI
FAQ
How does ChatGPT’s achievement of 1 billion monthly active users compare in terms of the speed specifically?
Based on Sensor Tower data, ChatGPT reached 1 billion monthly active users about three years after launch. Its speed surpasses Google Maps, TikTok, Instagram, and YouTube to reach the same milestone, making it the fastest application on record to reach this number.
How much did installing Claude affect ChatGPT usage habits?
Sensor Tower’s report shows that for ChatGPT users who installed Claude in the United States in Q1 2026, time spent using ChatGPT was 5% lower one month after installation than the average over the eight months prior. Sensor Tower said this was a shift in time allocation, not user churn.
What stage is Anthropic’s IPO filing currently at?
Anthropic secretly submitted its application on June 1, 2026. A confidential filing allows the company to avoid disclosing draft registration statement details publicly before a formal listing; the specific IPO timeline, pricing, and stock exchange for listing have not been announced yet.
