ChatGPT's market share falls below 50% as Gemini and Claude gain ground, signaling a shift in how users choose AI assistants.

What happened: ChatGPT's share of the AI assistant market dropped to 46.4% by May 2026, down from over 50% in January, while Gemini climbed to 27.7% and Claude reached 10.3%, according to analytics firm Sensor Tower. ChatGPT remains the largest by monthly users (over 1.1 billion) but is no longer dominant.

Why it matters: Users are increasingly willing to switch between assistants based on brand values and perceived fit for their needs, not just features—a shift made visible when OpenAI's defense department deal in February triggered a measurable spike in ChatGPT uninstalls. Gemini's growth is driven by integration with Google's ecosystem, while Claude has built a strong reputation for productivity tasks and now leads the field with a 13% subscription conversion rate, suggesting lasting revenue potential that investors will watch closely.

What to watch: By May, ChatGPT was serving ads to an average of 17% of daily users as the company expands monetization beyond subscriptions. In the U.S. market, people are projected to spend over $4.2 billion（約6700億円） on AI apps in the first half of 2026, more than double the $1.83 billion（約2900億円） spent in the same period of 2025, though growth rates are decelerating as the market matures.