OpenAI's ChatGPT Loses Majority AI Market Share as Gemini and Claude Surge

ChatGPT commanded over 50% of the AI assistant market until January 2026, but by the end of May that figure had fallen to 46.4%, according to Sensor Tower's State of AI Report. The throne is wobbling. Gemini now holds 27.7% of the market, while Claude accounts for 10.3%. Grok, Perplexity, DeepSeek, and Meta AI each hold less than 5%. ChatGPT became the fastest app ever to reach 1 billion monthly users. But dominance is fading fast. OpenAI's deal with the U.S. Department of Defense in February triggered a measurable spike in uninstalls — suggesting brand trust and values alignment matter to users, not just features. Anthropic's Claude has gained a strong reputation for productivity use cases and is closing in on ChatGPT's user-retention rate. Thirteen percent of Anthropic's users are paying for a subscription plan, a conversion rate that leads the field. In H1 2026, people are on pace to spend over $4.2 billion on AI apps, compared to $1.83 billion in H1 2025 — a jump suggesting the industry is shifting from pure growth toward monetization.