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.
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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.
[1]: https://privacy.claude.com/en/articles/10023638-why-am-i-rec...
Then the issue is failure to filter copyrighted content for most of the book and only successfully protecting 1 poem.
The issue is relying on an LLM to perform accurate OCR and then using it to interpret art.