ChatGPT is still the most widely used AI assistant in the world, but its dominance is easing. New data from Sensor Tower shows OpenAI’s chatbot slipped below 50% market share for the first time, marking a notable shift in the fast-moving AI assistant market.
The change comes more than three and a half years after ChatGPT’s debut and reflects a period in which users have increasingly tried alternatives such as Google’s Gemini, Anthropic’s Claude and xAI’s Grok. Sensor Tower’s State of AI Report for 2026 suggests the market is becoming more competitive as people move between products rather than staying loyal to a single assistant.
Despite the decline in share, ChatGPT continues to have the largest audience by a wide margin. Sensor Tower estimates the service has more than 1.1 billion monthly users. Gemini follows with 662 million monthly users, while Claude has 245 million. Other assistants, including Grok, Perplexity, DeepSeek and Meta AI, each hold less than 5% of the market.
OpenAI’s chatbot has grown rapidly. Sensor Tower recently said ChatGPT became the fastest app ever to reach 1 billion monthly users. OpenAI itself measures usage differently, reporting weekly active users rather than monthly totals. The company last said it had 900 million weekly active users in February.
Until January, ChatGPT held more than half of the AI assistant market. By the end of May, its share had fallen to 46.4%, according to Sensor Tower. Gemini had risen to 27.7%, while Claude reached 10.3%.
Sensor Tower said the data points to a user base that is increasingly willing to switch among tools based on product features, ecosystem fit and brand perception. The report also highlighted that events beyond product performance can affect usage trends.
For example, OpenAI’s agreement with the U.S. Department of Defense in February coincided with a measurable rise in ChatGPT uninstalls, indicating that trust and alignment with user values may matter as much as technical capability for some customers.
Gemini’s growth appears tied in part to its integration with Google’s broader suite of services. Claude, meanwhile, has built a reputation around productivity and is narrowing the gap with ChatGPT in user retention.
Even as competition intensifies, the overall AI app category is still expanding. Sensor Tower estimates that in the first half of 2026, users are on track to download nearly 2.3 billion AI apps and spend more than $4.2 billion on them. That compares with $1.83 billion in spending in the first half of 2025.
At the same time, the report says growth rates for both downloads and spending have slowed, suggesting the market may be entering a more mature phase. In Asia, downloads fell 3.3% in the first quarter of 2026, the region’s first decline, with China and India driving the dip. Asia still leads in total downloads, but North America and Europe outpace it in in-app spending.
The report also found that time spent in AI apps is rising sharply, with total hours projected to climb from 17.2 billion in the first half of 2025 to about 36 billion in the first half of 2026. The top three assistants account for 89% of time spent in AI assistant apps.
OpenAI has also started testing ads in ChatGPT, beginning in February. Sensor Tower says ad exposure has grown gradually, and by May about 17% of daily users were seeing ads.
Software and shopping are the largest advertising categories inside ChatGPT so far, followed by media and entertainment, and food and dining. The company is also sending more referral traffic to retailers such as Target, Walmart and Costco as shopping features expand. Amazon, which has blocked ChatGPT’s web crawlers, has seen little change in referral traffic from the platform.
The report suggests that on-platform AI tools can influence shopping behavior when users adopt them. Amazon’s Rufus assistant has shown flat growth, while Walmart’s Spark has gained momentum. Sensor Tower also said users who engaged with Rufus spent more time in Amazon’s app and converted at higher rates than those who did not.