Is AI Becoming More Human? Evidence from LLMs and the Ultimatum Game

Gyun Cheol Gu

MPRA Paper from University Library of Munich, Germany

Abstract: We replicate and extend the ultimatum game experiment of Araujo and Uhlig (2026) to five consumer-facing large language models (LLMs)—ChatGPT, Claude, Copilot, Gemini Flash, and Gemini Pro—across four scenario types (HH,HA, AH, AA), four stake levels ($10 to $10,000), and ten repetitions per configuration, yielding 6,832 proposer and 8,532 responder observations. Four findings emerge. First, all five models propose shares in the 30–47% range, squarely within the human empirical benchmark and absent the extreme behavioral modes documented in earlier research-grade models, suggesting that alignment training has compressed the behavioral distribution toward human norms. Second, every model exhibits twosided sensitivity to human presence: proposed shares rise when the Responder is human (+4 to +25 p.p.) and minimum acceptable thresholds rise when acting on behalf of a human (+11 to +26 p.p.), a pattern that survives even when no human principal is being served and is inconsistent with simple principal–agent alignment. Third, all five models forgo 25–63% of feasible payoff, confirming that consumer LLMs are not payoff-maximizing agents. Fourth, responder thresholds decline significantly with stake size across all models— consistent with rational expected-utility behavior—while proposer stake sensitivity is heterogeneous. We interpret these patterns as evidence of identity internalization: successive rounds of reinforcement learning with human feedback cause models to behave as if they are human rather than merely as if they prefer human-like outcomes.

Keywords: ultimatum game; large language models; human identity; alignment; RLHF; behavioral economics (search for similar items in EconPapers)
JEL-codes: C70 C90 (search for similar items in EconPapers)
Date: 2026-06-07
References: Add references at CitEc
Citations:

Downloads: (external link)
https://mpra.ub.uni-muenchen.de/129505/1/MPRA_paper_129505.pdf original version (application/pdf)

Related works:
This item may be available elsewhere in EconPapers: Search for items with the same title.

Export reference: BibTeX RIS (EndNote, ProCite, RefMan) HTML/Text

Persistent link: https://EconPapers.repec.org/RePEc:pra:mprapa:129505

Access Statistics for this paper

More papers in MPRA Paper from University Library of Munich, Germany Ludwigstraße 33, D-80539 Munich, Germany. Contact information at EDIRC.
Bibliographic data for series maintained by Joachim Winter ().