[SamBam]

Did they also test it by asking for fake information?

Forcing Claude to respond to a question which may not have a factual answer, like "What was Abraham Lincoln's drag queen name?" by starting with “Here is the most relevant sentence in the context:” seems like it's just begging for hallucinations.

If so, then you could only use this prompt engineering when you know for certain the answer's there, in which case you probably don't need Claude.

[M4v3R]

To verify you could either do a simple text search through the source document or utilize a 2-shot approach to double check the answer. Just take the answer from the first step and then ask the model again:

    Given the following document: <document text>
    Does this document support the following statement: <statement from step 1>

The downside of course is that you pay twice for the inference.