Biden announced he's ending his bid for the presidency via X (formerly twitter).

Sources:

• https://www.bbc.com/news/articles/c1e5xpdzkd8o
• https://edition.cnn.com/politics/live-news/biden-trump-election-07-21-24/index.html
• https://www.nbcnews.com/politics/2024-election/president-joe-biden-drops-2024-presidential-race-rcna159867