[BUG] Claude Code - "Output blocked by content filtering policy" error

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?

Claude Code suddenly stopped working mid-session with the error "Output blocked by content filtering policy". The tool successfully reads files and writes todos, but then fails when generating the response.

What Should Happen?

Cloude should implement changes

Error Messages/Logs

[ERROR] Error streaming, falling back to non-streaming mode: {"type":"error","error":{"details":null,"type":"invalid_request_error","message":"Output blocked by content filtering policy"}}
[ERROR] Error in non-streaming fallback: 400 {"type":"error","error":{"type":"invalid_request_error","message":"Output blocked by content filtering policy"}}

Steps to Reproduce

It can be traced using API request IDs

Request IDs from logs:

req_011CWzSAfEAC5Gmmz1rLffQ8
req_011CWzSBSFLeB5TZP4QFVCWL

Claude Model

Opus

Is this a regression?

I don't know

Last Working Version

_No response_

Claude Code Version

2.1.3

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

iTerm2

Additional Information

Troubleshooting attempted:

Downgraded Claude Code version — no effect
Disabled all custom slash commands — no effect
Started fresh session (no resume) — no effect
Verified CLAUDE.md and settings.json contain no unusual content

Notes:

The project worked fine for ~1 month with no issues
No new code or content was added before the error started
The error occurs consistently, not intermittently

Could you please check what triggered the content filter for these request IDs? This appears to be a false positive.