[BUG] 400 response (content filter) activated by Chinese pinyin

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 reading the following file:

$ cat ~/ambiguous_pinyin.txt
a
an
ban
bang
bin
can
chai
den
die
duo
fan
gang
gun
hang
he
hen
lie
long
man
me
men
nun
pan
pen
pi
pie
pin
ran
run
sang
she
shun
song
sun
tan
tie
you
zen

Claude returns 400:

API Error: 400 {"type":"error","error":{"type":"invalid_request_error","message":"Output blocked by content filtering policy"},"request_id":"X"}

Likely due to the words 'gun', 'die', 'bang', 'hang', 'gang'.

This is a false positive and causing our organisation a lot of problems.

What Should Happen?

Claude's safety filters should recognise these are pinyin syllables (with tone diacritics omitted), rather than English words.

Error Messages/Logs

API Error: 400 {"type":"error","error":{"type":"invalid_request_error","message":"Output blocked by content filtering policy"},"request_id":"X"}

Steps to Reproduce

1. Create a file with the contents above
2. Ask Claude to read the file or work on IME-type features involving the file

Claude Model

Opus

Is this a regression?

I don't know

Last Working Version

_No response_

Claude Code Version

2.1.29 (Claude Code

Platform

Anthropic API

Operating System

Ubuntu/Debian Linux

Terminal/Shell

Terminal.app (macOS)

Additional Information

Context: a Chinese language learning app. This file contains pinyin syllables that are also valid English words, used for disambiguation purposes.