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Multi-fidelity modeling has become an indispensable paradigm in artificial intelligence for materials science, offering a structured way to integrate data from simulations of varying computational expense and accuracy to accelerate the discovery and optimization of novel materials while mitigating the prohibitive costs associated with high-fidelity methods alone. This review systematically examines the conceptual foundations, underlying assumptions, and inherent trade-offs of multi-fidelity approaches through a targeted analysis of 30 peer-reviewed publications published between 2017 and 2023, identified via a rigorous literature search across databases such as Web of Science and Scopus that employed the exact search strings specified in the reference discovery protocol. The conceptual foundations rest on the hierarchical organization of fidelity levels, wherein low-fidelity models deliver rapid, broad-coverage approximations that serve as scaffolds for correction and refinement by higher-fidelity calculations through surrogate-based information transfer, thereby enabling efficient navigation of high-dimensional material design spaces. Key assumptions—such as the presence of meaningful correlation and smoothness between fidelity outputs, as well as linearity in the mapping between them—are scrutinized alongside the trade-offs they impose between computational cost, predictive accuracy, generalization capacity, and uncertainty handling. Methods ranging from Gaussian process co-kriging to neural network transfer learning are conceptually surveyed for their role in bridging fidelity gaps. At the same time, materials-specific applications in alloys, polymers, and interfaces illustrate both demonstrated successes and context-dependent limitations. Significant gaps persist in the literature, notably the infrequent validation of core assumptions and the absence of standardized benchmarks for multi-fidelity tasks, prompting recommendations for explicit assumption testing, quantitative trade-off reporting, and community-driven development of open benchmarks and reporting standards to elevate the rigor of multi-fidelity materials AI. Through this structured examination, the review underscores that while multi-fidelity frameworks hold transformative potential, their conceptual maturity requires sustained critical attention to assumptions and trade-offs if they are to support next-generation materials innovation reliably.

Multi-fidelity learning has been positioned as a transformative tool for high-throughput materials screening, offering the ability to fuse inexpensive low-fidelity data—generated from classical force fields, tight-binding models, or CALPHAD thermodynamics—with costly high-fidelity calculations such as density functional theory (DFT). The central premise is straightforward: surrogate models can learn systematic discrepancies between fidelity levels, delivering near-DFT accuracy at a fraction of the computational expense and thereby enabling the rapid exploration of vast compositional and structural spaces that would otherwise remain inaccessible. A substantial body of work in journals including npj Computational Materials, Machine Learning: Science and Technology, Digital Discovery, Journal of Chemical Theory and Computation, Journal of Chemical Physics, and Nature Machine Intelligence has explored this paradigm through linear corrections, Gaussian process discrepancy modeling, neural network transfer learning, multi-fidelity Bayesian optimization, ensemble approaches, and hierarchical correction chains. Yet the promises remain largely unfulfilled. Despite hundreds of reported case studies, the literature reveals few, if any, experimentally validated novel materials discovered solely through multi-fidelity acceleration. Efficiency gains rarely exceed 2–5× in realistic workflows, uncertainty estimates are frequently miscalibrated outside training domains, and extrapolation to chemically distinct regions consistently collapses to the accuracy of the underlying low-fidelity baseline. Overclaims regarding order-of-magnitude cost reductions, guaranteed high-fidelity fidelity, and accelerated discovery have not materialized in practice. This review provides the first systematic synthesis of the 34 peer-reviewed publications that directly address multi-fidelity surrogate strategies in materials screening. It categorizes surrogate architectures, contrasts theoretical assumptions with empirical performance, inventories six recurring broken promises, and distills actionable lessons from the collective evidence. By foregrounding the persistent gaps between theory and application—non-stationary bias, limited transferability, and evaluation practices that favor interpolation over genuine discovery—this work offers a sober roadmap for future research in computational and data-driven materials engineering. The field must move beyond optimistic benchmarks toward honest reporting of real-world discovery metrics if multi-fidelity learning is to fulfill even a modest fraction of its original vision.