ChatGPT is just about holding on to having a majority marketshare in the category it pioneered.

The latest SimilarWeb data for May 2026 puts OpenAI’s flagship at 52.7% of generative AI web traffic — down from 76.4% just twelve months ago. That’s a 23-plus point erosion in a single year, with the pace of decline showing no signs of letting up. At this rate, ChatGPT falling below 50% is a question of when, not if.

Gemini has been the principal beneficiary. Google’s AI assistant has climbed to 27.3% in May, compared to 8.9% a year ago. The trajectory has been remarkably consistent — Gemini was at 20.3% six months ago, crossed 25% in March, and has kept building. The platform has grown its traffic share more than three times over in twelve months, powered by ecosystem integration across Android and Google’s broader product suite, and a steady cadence of model releases that have kept users coming back.

The more striking story in the May data, though, belongs to Claude. Anthropic’s assistant has reached 8.9% traffic share — up from just 1.6% a year ago and 2.0% six months back. The acceleration in the last quarter has been sharp: Claude was at 6.0% in February, meaning it has added nearly three percentage points in three months. Earlier app data had flagged this momentum — Claude’s DAU share on mobile jumped from 4% in February to 10% in March. The May web traffic numbers confirm that the trend has held.

The rest of the field has been relatively static. DeepSeek is at 4.0%, up slightly from a 3.4–3.8% band it has occupied for most of the past year, never quite converting its early 2025 viral moment into lasting structural gains. Grok sits at 2.8%, where it was a year ago, despite strong year-over-year growth numbers at earlier points. Copilot holds at 2.0%, Perplexity at 1.3%.

The numbers at the top, though, are what matter. A year ago, ChatGPT operated close to a monopoly in this space. Today it has two genuine challengers, with Claude’s rise adding a third player to what was, until recently, essentially a two-horse race. Web traffic share is not engagement depth — ChatGPT’s DAU/MAU ratio has historically been nearly double Gemini’s, suggesting OpenAI’s users remain more habitual even as its headline share slips. But a drop from 76% to 52% in twelve months is not a number that management can explain away with engagement metrics alone.

The question heading into the second half of 2026 is whether any of the current momentum curves change direction. Gemini’s growth has been powered by Google’s distribution machine, and there’s little reason to expect that engine to stall. Claude’s rise has been faster than almost anyone anticipated — and the May figure suggests it still has room to run.