ChatGPT's AI Assistant Share Falls Below 50% for the First Time as Rivals Surge

The balance of power in the AI assistant market has reached a turning point. According to the "State of AI 2026" report published by market research firm Sensor Tower on June 16, ChatGPT's global share fell to 46.4% at the end of May, slipping below 50% for the first time since its debut in November 2022. As Gemini and Claude climb, a market that was once a one-horse race is entering a phase of genuine competition.

The Current Standings, by the Numbers

Sensor Tower calculates share using a deduplicated count of users across mobile apps, mobile web, and desktop web (its "True Audience" metric). The breakdown as of May is as follows.

These three services alone account for roughly 90% of the time spent on AI assistant apps. Note, however, that the ranking by user count differs from the ranking by time spent: by time spent, the top three are ChatGPT, DeepSeek, and Gemini. Claude's 10.3% audience share reflects how many people use it, which is a separate matter from how long they stay.

Still the Largest, No Longer the Majority

In absolute user numbers, OpenAI still stands out. ChatGPT crossed 1.1 billion monthly active users in May, becoming the fastest app ever to reach that scale — outpacing TikTok, YouTube, and Instagram. That is an unambiguous achievement in its own right.

Share is falling nonetheless because the overall market is expanding even faster. ChatGPT held 65.3% in December 2024, 52.8% in December 2025, and 46.4% in May 2026 — a downward trend that has continued for 18 straight months. It dropped below 50% in March of this year.

On the revenue side, OpenAI was reportedly generating 2 billion USD per month (about 320 billion yen) as of early 2026, with more than 50 million paying subscribers. Revenue per user has, if anything, been rising: as of May, the company was serving ads to roughly 17% of its daily active users and had expanded shopping integrations with retailers such as Walmart, Target, and Costco. This is a strategy that favors monetizing at scale over converting users into subscribers — a reasonable bet given a base of 1.1 billion people, but also a choice that changes how the free product feels to use.

*1 USD = 160 JPY (as of June 17, 2026)

How Default Placement Lifted Gemini

Gemini's monthly users grew from 533 million in December 2025 to 662 million in May, a gain of 129 million in five months. That growth owes less to dramatic capability gains than to how the product is distributed — that is, to where it is placed.

Google has embedded Gemini at the operating-system (OS) level of Android, replacing Google Assistant on the world's most widely used mobile platform. It is also built into Gmail, Google Docs, Sheets, Slides, and Drive by default, and on devices running Google's own "Tensor" chips it handles everyday tasks — setting alarms, sending messages, controlling smart home devices — on the device itself (on-device), meaning it works even offline. For users who live inside Google's services, Gemini is not a competing service to download separately; it is "the AI that was already there."

That is a different playing field from ChatGPT, which you must deliberately install and log into, or Claude, which is used mainly through the web and an API. A service installed by default is not weighed against alternatives by users — it is simply used. Gemini's rising share is, in large part, the compounding result of that "advantage as the default setting."

Claude's Growth Shows in Paid Conversion, Not Just Users

The steepest growth belongs to Claude. Its monthly users expanded from 60.2 million in December 2025 to 245 million in May — roughly a fourfold increase in five months, and a 452% rise year over year. In the United States specifically, its share climbed from about 4.4% in December 2025 to about 14% in May.

Yet the most striking figure in Claude's profile is not its user count but its paid conversion rate. Of its 245 million users, 13% subscribe to a paid plan — the highest level among all AI assistants tracked by Sensor Tower. Given that the typical free-to-paid conversion rate for consumer software is said to sit around 2% to 5%, that figure is exceptional.

This gap may owe less to Claude skillfully nudging free users toward paid tiers than to a competitor's circumstances. When ChatGPT shifted to showing ads to a portion of its users, those who had been inclined to "pay to avoid ads" gained a reason to look elsewhere — and Claude has become the destination. Claude's churn rate has also been declining since March, suggesting that the new users it attracts are staying.

What It Means for OpenAI Ahead of Its IPO

The timing of the report is hard to overlook. On June 8, OpenAI filed confidentially for an initial public offering (IPO) with the U.S. Securities and Exchange Commission (SEC) — the first formal step toward going public. Investors will now have to weigh two facts in tension: on one side, 1.1 billion users and the fastest user acquisition in app history; on the other, 18 months of declining share. A falling share figure does not mean ChatGPT is shrinking — it means others are growing faster. For a company preparing to go public, those two things are not the same.

Summary

A market in which a single product holds 65% may look competitive, but it is effectively close to a monopoly. When that figure falls to 46%, with rivals at 28% and 10% and with real switching behavior among users, the category finally becomes a genuine "market." ChatGPT remains the leader, but it is no longer the only answer. Gemini wields the structural strength of default placement, and Claude the industry's highest paid conversion rate — each with a different weapon. The latest numbers show that choosing an AI assistant has, in the truest sense, become a real choice.