A required field made my AI fabricate statistics

I run a pipeline that generates explainer articles. LLM in the middle, structured output, published in several languages. It had been running for a while and the articles looked good: clean layout, a chart, and near the top of each one a confident little box with a statistic. Something in the shape of "68% of people never change the default." A number, a source, an authoritative ring to it. Not one of those numbers had been researched. The pipeline had never looked up a single statistic in its life. It asked the model for a number and printed whatever came back. I did not find this through a clever eval. I found it while cleaning up something unrelated and actually reading the prompt. The field that forced a lie The output schema had a required field. statistic.text and statistic.source , described in the prompt as an "eye-catching stat" for the top of the article. Required. Every article had to have one. The prompt also, helpfully, told the model what to do when it did not have a real number. It said to round to a safe order of magnitude. And it said to strip the year off the source, so the article would look evergreen instead of dated. Read that back slowly. The instructions were: always produce a statistic, make up a plausible magnitude if you have to, and remove the one piece of metadata that would let anyone check it. That is not a prompt that occasionally allows a hallucination. That is a prompt that requires one, every single time the model does not happen to know a real figure. So it produced them, confidently, in every language, each wearing a real-sounding source: a named institute, an industry association, a government statistics office. None of it had been looked up when it was written. This was content people actually act on, which is exactly the category where being wrong is not a rounding error. There was a second engine doing the same thing in the chart code. The block that generated the data visualization asked the model for "actual statistics from