A sobering new sign for OpenAI as ChatGPT competitors gain ground

ChatGPT's share of the global AI assistant market has fallen below 50% for the first time, reaching 46% by May, according to Sensor Tower's "State of AI 2026" report. This marks a significant shift since ChatGPT's initial release in November 2022. The data, which measures usage across desktop, mobile apps, and the mobile web in 25 markets, shows Google's Gemini holding 28% market share and Anthropic's Claude at 10%. In the United States specifically, Claude's market share increased from 5% in December 2025 to 14% in May. Sensor Tower suggests that user concerns regarding OpenAI's deal with the U.S. Department of Defense may have contributed to this decline. While OpenAI stated its deal with the Pentagon includes similar "red lines" to Anthropic's previous agreement, it permits the use of ChatGPT for "all lawful purposes," a broader scope that reportedly led some users to switch to Claude. Despite the market share decrease, ChatGPT achieved a milestone in May, becoming the fastest mobile app to reach one billion users, with a total of 1.11 billion users worldwide across all platforms, still surpassing Gemini's 662 million and Claude's 245 million users.