OpenAI's ChatGPT recorded 3.7 million U.S. downloads in its first 40 days, while Grok had 500,000 and Claude had 200,000 U.S. downloads in that period.

From the articleMeta’s Muse reaches 10 million U.S. downloads in 40 days, a milestone matched by just 11 other apps | МежаAlso in Meta’s Muse hits 10M US downloads in 40 days, a milestone reached by only 11 other apps