Twitter’s widespread Monday glitches were caused when a single engineer—the last remaining site reliability engineer working on Elon Musk’s plan to cut off free access to third-party Twitter data—made a change to the company’s code and “broke” the site, according to an employee who spoke with Platformer. Musk was apparently furious at the development. “A small API change had massive ramifications,” he tweeted Monday afternoon. “The code stack is extremely brittle for no good reason. Will ultimately need a complete rewrite.” Just 550 full-time engineers remain at the company, Platformer reported.