ChatGPT, OpenAI’s popular chatbot, is estimated to have reached 100 million monthly active users in January, just two months after its launch, making it the fastest-growing consumer app in history, according to a UBS study (SIX:UBSG) published on Wednesday.

The report, which cites data from analytics firm Similarweb (NYSE):SMWB), notes that an average of about 13 million unique visitors used ChatGPT per day in January, more than twice as many as in December.

“In the 20 years we have been following the Internet world, we do not remember a faster growth of a consumer application,” the UBS analysts write in their note.

TikTok took about nine months from its global launch to reach 100 million users and Instagram 2 <>/<> years, according to data from Sensor Tower.

ChatGPT can generate articles, essays, jokes, and even poetry in response to instructions. OpenAI, a privately held company backed by Microsoft Corp (NASDAQ:MSFT), made it available to the public free of charge at the end of November.

On Thursday, OpenAI announced a $20 monthly subscription, initially for U.S. users only. According to the company, this would provide a more stable and faster service, as well as the opportunity to test new features earlier.

Analysts believe the viral launch of ChatGPT will give OpenAI an edge over other artificial intelligence (AI) companies. The growing use, while imposing considerable computing costs on OpenAI, has also provided valuable information to help train chatbot responses.

The company says the subscription revenue will help cover IT costs.

The availability of the tool has raised questions about facilitating academic dishonesty and misinformation.

Last month, Microsoft announced another multibillion-dollar investment in OpenAI in the form of cash and cloud computing supply.