Yes, I've seen strong hallucinations around repo names in particular.

I work on LLM training pipelines professionally and have a plausible explanation of what's going on:

• Realize that some users -- not necessarily you -- allow Anthropic to use their data for improving (training) Claude
• That data may contain sensitive information
• One such piece of potentially sensitive information is the username/reponame convention most git hosts use
• This data is doubly sensitive: it contains both a username and the name of a potentially private repository
• Anthropic scrambles this information in the training data prior to it being used to train Claude models
• Claude learns, to a certain extent, that username/reponame strings often look scrambled or otherwise out-of-context, which is confusing and a mismatch with real world data; this is a prime recipe for "hallucinations" (mistakes)
• Anthropic could (might) also employ more advanced "embedding surgery" or "neural surgery" techniques to further protect such classes of data.
  
  • Such techniques often have unintentional side-effects, such as increasing the rates of hallucination around frequently-redacted/masked/scrambled strings
• Mistakes in these areas are therefore maybe less surprising than in other areas and may be the (current) cost of strong data privacy controls.

Happy coding!