Redesigning source control at Anthropic
Anthropic built custom source control after daily merges jumped from 2,500 to over 30,000.
Anthropic describes building its own source-control system after daily merged code changes rose from about 2,500 in May 2026 to more than 30,000 in September. Simon Willison notes the surge and overlays public 2026 model release dates, guessing that Fable and Mythos-class models helped drive the internal coding volume. Those markers reflect public releases, not when the models became available inside Anthropic.
- Merged changes rose from about 2,500 per day in May 2026 to over 30,000 in September.
- Anthropic built a custom Git alternative to handle the higher change rate.
- Willison links the jump to 2026 model releases, including Fable and Mythos-class models.
Redesigning source control at Anthropic Interesting piece from Anthropic describing why and how they built their own custom alternative to Git, based on the dramatic increase in rate of changes to their code after the past six months. In May 2026, Anthropic averaged around 2,500 code changes merged per day; as of September, we merged over 30,000 per day. They included a chart showing those changes. I had Claude modify their chart ( code here ) to add markers for the public releases of each of their models in 2026: This shows public release dates, not the date when models became available for Anthropic's internal use. My guess is that the introduction of Fable/Mythos class models is a key…
This source does not provide full text. Read it at simonwillison.net.