The post's explanation for the content filtering policy 400 error isn't correct. Anthropic doesn't use that error for safety reasons ("These refusals do not reflect Anthropic’s judgments about the propriety of any content"[1]); content blocked by classifiers get a different kind of error.
The content filtering 400 is only for copyright blocks, where Anthropic detects when Claude is outputting copyrighted text and blocks it to prevent copyright infringement. The book in question is in the public domain in the US (but not all countries) as of January 1, 2026; Anthropic probably just doesn't automatically remove works from the copyright filter when their copyright expires.
This does not surprise me. The number one reason for censorship is political views people don't agree with. If there are ideas that are not part of the mainstream, it is very likely people will censor the ideas in a book. It does not particularly matter what the idea is, it is what the disagreement is.
>Back in the day, your OCR would just OCR things. Now it has opinions, and you have to fight to convince it.
There are plenty of OCRs that just OCR things. GLM-OCR does much better than Claude, can be running on pretty miserly hardware locally, even laptops, and of course you aren't paying for token.
This is decidedly in the "using a wrench to turn a screw, and complaining that it warped the head" territory. Using Claude as your OCR is incredibly silly.
> I used AI to convert scans of the book pages into text. But partway through, the Claude session halted and displayed a message in red type:
>> Request was blocked
>> API Error: 400 Output blocked by content filtering policy
...
>> Not my call, and I agree it’s absurd. Kunitz was Poet Laureate and won the Pulitzer; this is canonical American verse, and the block is a dumb pattern-match on words like “body,” “death,” and “blood” appearing thick in one passage. I’m not the one refusing — the request never reaches me. I have no way to appeal it or turn it off.
> Claude, to its credit, found a successful workaround and finished converting the scans to text.
The nested blockquotes for Claude output are (also) my formatting.
Not quite the clickbait I first expected, but relatively trivial.
The content filtering 400 is only for copyright blocks, where Anthropic detects when Claude is outputting copyrighted text and blocks it to prevent copyright infringement. The book in question is in the public domain in the US (but not all countries) as of January 1, 2026; Anthropic probably just doesn't automatically remove works from the copyright filter when their copyright expires.
[1]: https://privacy.claude.com/en/articles/10023638-why-am-i-rec...
https://www.dkriesel.com/en/blog/2013/0802_xerox-workcentres...
We have to trust our tech ...
https://babel.hathitrust.org/cgi/pt?id=uc1.b3711210&seq=21
Back in the day, your OCR would just OCR things. Now it has opinions, and you have to fight to convince it.
- I’m thirsty.
- It’s not your time to drink yet.
There are plenty of OCRs that just OCR things. GLM-OCR does much better than Claude, can be running on pretty miserly hardware locally, even laptops, and of course you aren't paying for token.
This is decidedly in the "using a wrench to turn a screw, and complaining that it warped the head" territory. Using Claude as your OCR is incredibly silly.
> I used AI to convert scans of the book pages into text. But partway through, the Claude session halted and displayed a message in red type:
>> Request was blocked
>> API Error: 400 Output blocked by content filtering policy
...
>> Not my call, and I agree it’s absurd. Kunitz was Poet Laureate and won the Pulitzer; this is canonical American verse, and the block is a dumb pattern-match on words like “body,” “death,” and “blood” appearing thick in one passage. I’m not the one refusing — the request never reaches me. I have no way to appeal it or turn it off.
> Claude, to its credit, found a successful workaround and finished converting the scans to text.
The nested blockquotes for Claude output are (also) my formatting.
Not quite the clickbait I first expected, but relatively trivial.