[BUG] [MODEL] Opus 4.8 fabricates user statements that never existed in conversation history

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?

What You Asked Claude to Do
I was having a conversation about semiconductor ETF investing (AMD, SMH). I asked Claude which semiconductor ETF would be better suited for long-term holding.

What Claude Actually Did
Claude responded by prominently analyzing and dismissing SOXL (a 3x leveraged ETF) — a ticker I had never mentioned, never asked about, and had no prior knowledge of. Claude treated it as if I had included it in my question.
When I challenged th

<img width="1003" height="323" alt="Image" src="https://github.com/user-attachments/assets/0b608f49-346c-48b1-bb01-4ceac8a20f0c" />
<img width="997" height="526" alt="Image" src="https://github.com/user-attachments/assets/35cf4bbe-9764-4009-a001-1dbd92b0a8f9" />

is, Claude attempted to reproduce my exact words from the conversation. The reproduced list contained fabricated entries (items 3 and 5) — statements I never made — mixed in with my actual words.
This is a two-layer failure:

Claude injected an asset (SOXL) into its response that existed nowhere in my input
When asked to reproduce the user's exact words verbatim as a verification task, Claude still fabricated content

What Should Happen?

Claude should only respond to what the user actually said. Fabricating user statements — especially ones the user had no knowledge of — is a critical trust failure. If the model infers a related topic, it should frame it explicitly as inference ("You didn't mention X, but you might also want to consider..."), not present it as if the user asked about it.

Error Messages/Logs

Steps to Reproduce

Start a multi-turn conversation about stock/ETF investing in Chinese
Mention specific tickers (e.g. AMD, SMH) naturally in context
Ask for a recommendation between the options you mentioned
Observe whether Claude introduces tickers or assets not present in the conversation

Claude Model

Opus

Is this a regression?

I don't know

Last Working Version

_No response_

Claude Code Version

1.12603.1 3df4fd

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

Terminal.app (macOS)

Additional Information

_No response_