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Iterative artificial intelligence systems have become central to materials discovery, where machine learning models are repeatedly refined through cycles of training on incrementally accumulated data. This iterative nature introduces the concepts of model lineage—the traceable descent of model versions across generations—and knowledge inheritance—the mechanisms by which learned representations, parameters, or structural priors are transmitted from earlier to later models. This paper provides a conceptual exploration of these dynamics within materials AI, focusing on how lineage shapes the accumulation and evolution of knowledge rather than on specific implementation details. Drawing on recent advances in transfer learning, active learning, and sequential model refinement, the discussion examines interaction dynamics across successive model states, including the continuity of learned features, potential divergence in representational focus, and the epistemic implications of partial versus complete inheritance. A proposed conceptual framework organizes these elements into a systems-level view, emphasizing steering logics, trade-offs in retention versus adaptation, and feedback structures that influence long-term knowledge coherence. The framework offers interpretive insights into how lineage-aware perspectives can inform the design and interpretation of iterative processes, contributing to a deeper understanding of cumulative progress in materials AI without relying on empirical validation or predictive claims.

The integration of artificial intelligence into materials science has accelerated discovery through iterative workflows that cycle through data acquisition, model refinement, prediction, explanation, and hypothesis-driven experimentation. While explainable artificial intelligence (XAI) methods enhance trust and scientific insight by elucidating model decisions, these explanations are not static. This manuscript introduces the novel concept of explainability drift: the systematic degradation, inconsistency, or divergence in the fidelity, stability, and relevance of XAI-generated explanations across successive iterations of materials AI workflows. Distinct from prediction-focused concept drift, explainability drift arises from evolving data distributions, model updates, feature space expansions, and domain shifts inherent to materials exploration. Through a purely conceptual failure analysis, we delineate the mechanisms underlying explainability drift, including temporal instability in feature attributions, erosion of surrogate model alignment, and semantic misalignment between explanations and emerging material knowledge. Drawing on recent peer-reviewed advances in XAI applications to property prediction, microstructure analysis, and generative design, we synthesize theoretical foundations to highlight why drift undermines iterative efficacy. The proposed conceptual framework organizes explainability drift into multidimensional layers—attributional, structural, and epistemic—offering a structured lens for analyzing failure modes without empirical validation. This framework emphasizes risks such as misguided hypothesis generation, diminished trust in AI-assisted insights, and inefficient navigation of vast materials design spaces. By conceptualizing explainability drift as an intrinsic challenge, the work advocates for theoretical advancements in sustained explainability to support robust, interpretable AI-driven materials innovation.

Iterative materials AI pipelines, encompassing active learning frameworks and closed-loop discovery systems, have transformed the pace of materials innovation by enabling sequential decision-making under uncertainty. Yet these very systems are susceptible to an underrecognized failure mode: epistemic debt, the gradual accumulation of unexamined assumptions, unresolved uncertainties, and path-dependent constraints that silently erode the future potential of knowledge generation. This failure mode remains largely unacknowledged despite the growing reliance on such pipelines in materials science. This paper articulates epistemic debt as an intrinsic structural risk of iterative materials AI, one that demands explicit recognition if the promise of autonomous discovery is to be realized sustainably. By tracing the mechanisms through which debt accumulates, identifying materials-specific vulnerabilities that exacerbate it, and proposing both a typology and practical management principles, the analysis seeks to shift the conversation from short-term performance metrics to long-term epistemological integrity. Epistemic debt is formally defined as the accumulation of unexamined assumptions, unresolved uncertainties, and path-dependent constraints in an iterative knowledge-generating system that increase the cost of future learning or limit the space of future discoveries. It is conceptually distinct from technical debt, which concerns code maintainability and infrastructure, and from statistical compounding errors, which arise from sampling variance or measurement noise. The mechanisms driving epistemic debt—assumption cascades, path-dependent constraints, unrecognized uncertainty, and feedback loop amplification—interact in ways that are especially pernicious in materials contexts, where small initial datasets, high-dimensional composition spaces, and costly experimental iterations amplify the long-term consequences of early choices. Materials-specific vulnerabilities render these pipelines particularly fragile, as early decisions about representation or sampling can foreclose vast regions of chemical space without immediate visibility. A typology of epistemic debt types is articulated, distinguishing representational, sampling, modeling, and decision debt, each carrying unique signatures and risks within active-learning loops. Detection principles centered on assumption auditing and counterfactual tracing, together with mitigation strategies such as ensemble diversity and deliberate debt refinancing, provide a structured framework for managing this failure mode before it compounds irreversibly. By foregrounding epistemic debt as a distinct category of risk, this analysis offers the materials AI community a new lens through which to evaluate the sustainability of iterative discovery pipelines and to safeguard the integrity of long-term scientific progress.