Support for the Claude Citations API

[simonw]

New API from Claude. Announcement. API docs. My blog post.

This is an interesting implementation challenge with two parts: first we need a way to attach documents (text, PDF or custom content JSON) to a prompt - the attachments mechanism should mostly handle this, but we need a way to flag "enable citations against this attachment".

Secondly, we need to store the citation information that comes back from the model - spans of text that have citation information attached to them. I started a separate issue in LLM core about that here:

• Design annotations abstraction for responses that are not just a stream of plain text llm#716

[simonw]

The easiest way to handle the attachments challenge might be to register fake content types - so you can do this:

llm -m claude-3.5-haiku \
  --at doc.pdf citations/pdf \
  --at doc.txt citations/text \
  "prompt goes here"

This is a tiny bit ugly - I always have trouble remembering if the filename or the content type comes first when using --at - but it would solve the problem neatly within our existing CLI design.

Another option would be to use a model option:

llm -m claude-3.5-haiku \
  -a doc.pdf -a doc.txt \
  -o citations 1 \
  "prompt goes here"

Here' the citations 1 option means "treat any PDF or TXT attachments as citation sources".

Might even be worth supporting both of these options - so really all -o citations 1 does is treat any PDFs as citations/pdf and any text documents as citations/text.