OpenAI's ChatGPT crossed the 1.1 billion monthly active user threshold in May, becoming the fastest‑growing online service ever. The milestone arrives as its dominance erodes; market‑share data shows ChatGPT holding 46.4% of the AI chatbot market, down from a near‑monopoly years ago. Competitors Gemini and Claude now claim 27.7% and 10.3% respectively.

The surge in overall chatbot usage fuels the shift. Gemini reports 662 million users and Claude 245 million, while spending on AI chat apps rose to $4.2 billion in the first half of this year, more than double last year's figure. Claude leads in paid conversions at 13% of its base, helped by strict free‑tier limits.

ChatGPT counters with ad integration, serving ads to roughly 17% of daily users and pushing referral links to retailers like Target and Costco. The data suggests users are increasingly fluid across platforms, diminishing any single bot's lock‑in power. OpenAI now faces a crowded market where growth no longer guarantees monopoly.