ChatGPT surpassed 1 billion active monthly users worldwide in May. According to Sensor Tower, this is the fastest achievement of such a level among apps.
It took ChatGPT about three years from launch to reach this milestone. In terms of growth rate, the service outpaced Google Maps, TikTok, Instagram and YouTube.
The record came at a time when OpenAI and Anthropic are actively preparing for IPOs. Reuters reports that Anthropic confidentially filed documents for an IPO in the US on Monday. OpenAI is also expected to do the same soon.
ChatGPT Reaches a Billion After Growth Slowdown
Back in December, it seemed that ChatGPT‘s growth was noticeably slowing down. From August to November 2025, the number of active monthly users increased by only 6%, reaching 810 million. At the time, it looked like the service was nearing its audience ceiling.
During the same period, Gemini users grew by 30%.
The slowdown was significant enough that OpenAI CEO Sam Altman sent an internal memo to employees marked as a “wake-up call.” In it, he urged the team to focus on improving personalization, service stability, and image generation.
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But the 1 billion user mark showed that the ceiling was higher than December data suggested. After talks of saturation, ChatGPT added about 190 million active users in six months.
Claude Grabs Some Attention From ChatGPT
According to Sensor Tower, US users who installed Claude in the first quarter of 2026 spent 5% less time in ChatGPT a month later. The comparison was made with their average usage over the previous eight months.
At the same time, Claude still lags far behind ChatGPT in audience size. In the second quarter of 2026, the service had about 56 million active monthly users worldwide.
However, in terms of growth rate, Claude looks much more aggressive. Over the year, its monthly audience grew by 640%, while ChatGPT grew by 62%.
This does not mean that users are massively leaving ChatGPT. Rather, they are starting to split their time between several AI services and use ChatGPT and Claude for different tasks.
A similar sentiment can be seen on Polymarket. There, traders estimate the probability that Anthropic will have the best AI model by the end of June at about 84%.
According to these bets, Anthropic currently leads OpenAI, Google and xAI in the race for AI leadership.
Which company will have the best AI model by the end of June? Source: Polymarket
Last week, Anthropic introduced Claude Opus 4.8 and announced that Mythos class models will become available to all clients in the coming weeks.
According to the company, Opus 4.8 outperformed GPT-5.5 in at least 12 benchmarks. The tests covered work tasks, AI agent tool usage, and long context processing.
Anthropic Filed for IPO a Day Before ChatGPT’s Record
Anthropic confidentially filed documents for an IPO in the US on June 1. This happened a day before the data was published showing that ChatGPT surpassed 1 billion active monthly users.
According to media, OpenAI is also preparing for an IPO. The company is working on filing documents with Goldman Sachs and Morgan Stanley. The possible listing could take place in the second half of 2026.
At the time of publication, Polymarket traders estimate the probability that Anthropic will go public before OpenAI at 74%.
Who Will IPO First: Anthropic or OpenAI? Source: Polymarket
