ChatGPT's share of AI prompt volume fell from 70% to 50% in six months, Comscore says -- Gemini and Claude are absorbing nearly all of what it lost

OpenAI's ChatGPT held 70% of all AI-assistant prompt volume in January 2026, according to Comscore's panel-based tracking. By June, that share had fallen to 50% -- while Google's Gemini nearly doubled, from 17% to 30%, and Anthropic's Claude grew more than fivefold, from 2% to 11%. A second, differently built measurement -- Similarweb's website-traffic tracker -- shows the identical direction on different numbers, which is the more interesting fact than either headline percentage: two measurements that count completely different things agree ChatGPT is losing relative ground, even as OpenAI's own disclosed user numbers keep climbing in absolute terms.

The decline didn't start in January. Similarweb's own tracker put ChatGPT above 86% of worldwide AI-platform traffic as recently as early 2025, and still above 73% last August -- meaning the fall toward the low 50s has been running for well over a year, not six months, and Comscore's Q2 report captures the most recent, steepest stretch of a longer slide rather than the whole story.

Comscore's Q2 2026 AI Intelligence Report is built from an opt-in panel of 500,000 to 1 million internet users whose browsing and app activity is tracked with consent, then weighted to represent the broader population -- the same methodology Comscore has used for TV and web ratings for two decades, applied here to what it calls 'AI prompt volume,' its term for messages sent to a chatbot. ChatGPT's slide happened while overall AI usage was still growing fast: ChatGPT's own desktop conversations rose to 168 million in June, and its multiplatform visitation grew from 59 million to 99 million over the prior year, per the report -- meaning the 20-point share loss reflects rivals growing faster, not ChatGPT shrinking.

The month-by-month split shows the shift wasn't a single event but a steady six-month slide, with Gemini and Claude both gaining share in every measured month rather than in one sudden jump:

Similarweb's own tracker, which counts direct visits to each assistant's website rather than sampling a user panel, put ChatGPT at 52.7% of worldwide AI-platform traffic as of late May 2026, with Gemini at 27.3% and Claude at 8.9% -- down from a January baseline in the mid-60s for ChatGPT. The remaining players are smaller and mostly flat on this tracker: DeepSeek at 4.0%, Grok at 2.8%, Microsoft's Copilot at 2.0% and Perplexity at 1.3%, none of them moving meaningfully in either direction this year. The two trackers don't agree on ChatGPT's exact share -- 50% versus 52.7%, measured about a month apart -- because they aren't counting the same thing: Comscore's panel captures prompts sent inside native apps and browser extensions a website-traffic count would miss entirely, while Similarweb can't see a query typed into a mobile app that never touches a browser. What they agree on is the trend line, measured two different ways: ChatGPT down, Gemini up sharply, Claude up from a small base.

None of this means ChatGPT is shrinking. OpenAI has said it crossed 900 million weekly active users in February, alongside a $110 billion funding round -- up from 400 million a year earlier. (A shrinking share of a fast-growing category can still mean more total users than a year ago; the two trends aren't in conflict, they're describing different things.) What Comscore and Similarweb are actually tracking is a widening field, not a shrinking company: users who once had ChatGPT as their only real option are trying Gemini, bundled free into Android and Search, and Claude -- and some of that trying is sticking.

“Publishers should stop asking 'how do we show up in ChatGPT' and start asking 'where is our audience actually asking questions.'” — Michael King, iPullRank, on Comscore's findings

Claude's 11% share (or 8.9% on Similarweb's count) is real, but it undersells where Anthropic's actual growth is happening. In Anthropic's own account of its business, presented alongside an April run-rate of $30 billion -- eight times the growth rate the company says it had planned for -- the fastest-growing piece isn't the Claude.ai chat website at all. It's Claude Code, whose weekly active users doubled in the first two months of 2026 and whose business subscriptions quadrupled over the same stretch, according to CEO Dario Amodei. None of that shows up in either tracker above, because Claude Code runs through a command line and API calls, not a browser tab or a chat window. Prompt-volume share and revenue share are simply not the same market.

The same two reports support three different winning stories, one for each company. OpenAI can point to 900 million weekly users and call the field bigger, not smaller, for ChatGPT. Google can point to Gemini's climb from 17% to 30% as proof its bundling strategy is converting. Anthropic can point past the chat-share numbers entirely to a revenue line neither tracker was built to see. All three claims are compatible with the same data -- which is the actual finding here: a category growing fast enough that every major player can tell a true story about winning it, using a different metric each time.