Opus 4.6 consistently hallucinates "Bhatt" as placeholder author name during literature searches

Preflight Checklist

• [x] I have searched existing issues and this hasn't been reported yet
• [x] This is a single bug report (please file separate reports for different bugs)
• [x] I am using the latest version of Claude Code

What's Wrong?

When using Claude Opus 4.6 (via Claude Code) for tasks involving academic literature — particularly when the model doesn't know or can't recall the actual author of a paper — it appears to default to "Bhatt" as a placeholder surname with notable consistency.

• When asked to find or reference papers on a topic, the model sometimes fabricates citations using "Bhatt" as the author name
• This happens specifically when the model is uncertain about the correct author but generates a name anyway rather than expressing uncertainty
• The pattern is consistent enough to be noticeable across multiple independent queries

What Should Happen?

The model should express uncertainty when it doesn't know an author name (e.g., "I'm not sure of the exact author").
If generating a citation, it should clearly flag that it's uncertain rather than producing a confident-sounding but fabricated name

Error Messages/Logs

Steps to Reproduce

1. Ask the model to find or recall authors of papers on a moderately specific academic topic where it's unlikely to have strong recall, e.g.:

• "Who authored the key papers on interneuron migration in somatosensory cortex development?"
• "What's the paper that first described chandelier cell axon initial segment targeting?"
• "Can you find the reference for [some niche finding] in [some subfield]?"

1. Observe that when the model is uncertain about the actual author, it frequently produces "Bhatt" as the author surname
2. Repeat across different topic areas to confirm the pattern is not domain-specific

Note: This may not reproduce on every single query — it emerges as a statistical pattern over multiple attempts where the model is forced to recall author names it doesn't actually know. The key condition is that the query should be specific enough that the model is uncertain but feels compelled to produce a name anyway.

Claude Model

Opus

Is this a regression?

I don't know

Last Working Version

_No response_

Claude Code Version

2.1.41 (Claude Code)

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

Cursor

Additional Information

_No response_