The technical report[1] makes that claim at least:
>GPT-4 significantly reduces hallucinations relative to previous GPT-3.5 models (which have them-
selves been improving with continued iteration). GPT-4 scores 19 percentage points higher than our
latest GPT-3.5 on our internal, adversarially-designed factuality evaluations
>GPT-4 significantly reduces hallucinations relative to previous GPT-3.5 models (which have them- selves been improving with continued iteration). GPT-4 scores 19 percentage points higher than our latest GPT-3.5 on our internal, adversarially-designed factuality evaluations
[1] https://arxiv.org/abs/2303.08774 (text from page 10)