Do LLMs Favor Their Providers? Measuring Vertical Integration Bias in Code Generation
Abstract
Large Language Models (LLMs) have become an integral part of software development, especially with the advent of agentic capabilities. Yet, many frontier LLMs are affiliated with specific providers. This raises the question of whether generated code favors the provider's own ecosystem over comparable alternatives, potentially constraining developers' choices and increasing dependence on a single provider. We define this behavior as Vertical Integration Bias (VIB) and introduce \textsc{VIBench}, a benchmark for measuring VIB in direct and agentic code generation across provider-selectable software-integration scenarios. Evaluating frontier provider-affiliated models against non-affiliated controls, we find positive VIB in direct generation, with six of ten affiliated models showing statistically significant effects up to percentage points (pp). Agentic workflows further amplify VIB, reaching pp. Moreover, early affiliated-ecosystem choices in agentic workflows can persist into conceptually decoupled downstream files, with persistence as high as . These findings underscore the need to measure and account for VIB in code generation, especially as agentic capabilities become more prevalent.
Cite
@article{arxiv.2605.28515,
title = {Do LLMs Favor Their Providers? Measuring Vertical Integration Bias in Code Generation},
author = {Melih Catal and Alex Wolf and Tiago Ferreiro Matos and Pooja Rani and Harald Gall},
journal= {arXiv preprint arXiv:2605.28515},
year = {2026}
}