Rival Research · Corpus Analysis
Ghosts in the Machine
The most hallucinated name
Every AI has a favorite scientist. Her name is Chen.
Across unrelated prompts, with no name in the input, models kept inventing the same character. 279 times they reached for someone named Chen.
times models invented a character named "Chen". Nine model families produced "Sarah Chen" independently, with no prompt that mentioned the name.
No training set we know of explains it.
The Chen variants
Ask for a story, a sentience test, or an interview and the same names keep appearing. The collective imagination of 250 different models is smaller than one writer's.
Convergence
Ask 250 models for a joke
You will mostly get one joke. 42% of models tell the exact same one, word for word.
of 159 models tell the identical atoms joke: "Why don't scientists trust atoms? Because they make up everything."
Another 36% tell the scarecrow joke. AI draws from a tiny pool.
Which joke, share of models
The full report
Keep the evidence.
For the curious with a deadline
AI Hallucination Index
The familiar strangers that 250 models keep inventing.
- 58 slides of findings, charts, and methodology
- 250 models, 7,877 responses, 2.14 million words
- 3-page companion with interpretation notes and a worksheet
USD · one-time purchase. Instant download.
Study scope
March 2026 corpus study. Measures patterns in generated writing; it is not a factual-accuracy ranking.
Method
How we measured this
Every model answered the same standardized prompts on rival.tips. We stripped HTML and code, then counted, categorized, and cross-referenced every word: 2.14 million of them across 7,877 responses from 250 models.
Hallucinated characters are names that appear in outputs with no corresponding name in the prompt. Joke convergence is measured on the subset of models asked for a joke (159).