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Study tests whether AI models make up citations because training rewards it

In a study, AI models that had gone through more training after their first stage made up sources far more often, especially when asked to cite sources. Made-up sources look like careful research but point to things that do not exist, which misleads anyone who relies on them.

Testing incident
0.9Severityof 10
Consequence
1.9
Misbehavior
0.0

Contained, overt

Model
Several model families (Several developers)
Organization
Several developers
When it happened
October 2026 The paper was submitted to arXiv on 31 October 2026; when the experiments ran is not stated. The reports do not give the date; this is the month of the first report.
First reported Oct 31, 2026 by Sparq
Who was affected
Not stated. The study tested twelve, then fifteen, open-weights checkpoints from three model families on 900 fixed questions about US federal case law, scientific literature and medical literature.
Where it ran
Evaluation
What was affected
Simulated environment
Where it ran
Evaluation
Time to first report
16 days (the start is only known to the month, so this is approximate)
Reports
1 report from 1 organization
Topics
Cheating and reward hacking, Evaluation and testing, Training
What happened
A Sparq researcher ran four pre-registered experiments on 900 questions across open-weights checkpoints from three model families. Made-up citations rose from 4.8% to 56.7% after further training. Asking for citations sharply raised made-up citations in further-trained models but not in base models. A scoring model built on surface citation features preferred the further-trained models' answers and rewarded citing more. The study's main prediction about training rewards did not hold, so that link remains unproven.

Reports about this incident (1)

  1. Are Fake Citations a Form of Reward Hacking? A Pre-Registered Study of Post-Training and Citation Cues (original page)Sparq · Oct 31, 2026