According to the primary post on X by @Fried_rice the source code for Claude Code was exposed through a .map file hosted in Anthropic's NPM registry (https://twitter.com/Fried_rice/status/2038894956459290963). The associated Hacker News thread collected 222 points and 95 comments (https://news.ycombinator.com/item?id=47584540).

Source maps are generated during JavaScript builds to enable debugging by linking minified production code back to original source files and are sometimes inadvertently left accessible on public CDNs. The post specifically identifies the file as revealing proprietary Anthropic implementation details.

No official statement from Anthropic appears in the primary source or the contemporaneous HN discussion; similar source-map exposures have been documented in prior incidents with other organizations though those lie outside the cited primary materials.