# W2: Model behavior and hallucination log

How Large Language Models Work: Foundations for Choosing and Applying LLMs at Work (FAST-14) · Lab 2: Base vs instruct vs reasoning models; hallucination hunt

Name: ______________________  Date: ____________

| Prompt | Base model: type / correct? | Instruct: type / correct? | Reasoning: type / correct / seconds |
| --- | --- | --- | --- |
| (a) to (e), one row each | | | |

| Hallucination hunt | Without source | With source |
| --- | --- | --- |
| Correct | | |
| Invented (count and one example) | | |
| "I don't know" / "not in source" | | |

Then answer in one paragraph: which model type would you use for the shop's quote questions, and what control would you require?

**Completion criteria**

- All 15 model and prompt cells are filled.
- Both hallucination counts are recorded, with at least one invented answer quoted.
- The paragraph links the behavior back to training (pretraining versus instruction or preference tuning versus reasoning training) and names a control such as grounding, citations, or human review.