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<article xmlns:xlink="http://www.w3.org/1999/xlink">
  <front>
    <journal-meta>
      <journal-title-group>
        <journal-title>Novi
Sad, Serbia
* Corresponding author.
sasa.brdnik@um.si (S. Brdnik); tjasa.hericko@um.si (T. Heričko)</journal-title>
      </journal-title-group>
    </journal-meta>
    <article-meta>
      <title-group>
        <article-title>Prospects of Explainability in the Hugging Face Hub Landscape</article-title>
      </title-group>
      <contrib-group>
        <contrib contrib-type="author">
          <string-name>Saša Brdnik</string-name>
          <xref ref-type="aff" rid="aff0">0</xref>
        </contrib>
        <contrib contrib-type="author">
          <string-name>Tjaša Heričko</string-name>
          <xref ref-type="aff" rid="aff0">0</xref>
        </contrib>
        <aff id="aff0">
          <label>0</label>
          <institution>Faculty of Electrical Engineering and Computer Science, University of Maribor</institution>
          ,
          <addr-line>Koroška cesta 46, Maribor</addr-line>
          ,
          <country country="SI">Slovenia</country>
        </aff>
      </contrib-group>
      <pub-date>
        <year>2024</year>
      </pub-date>
      <volume>000</volume>
      <fpage>0</fpage>
      <lpage>0003</lpage>
      <abstract>
        <p>Machine learning models are widely adopted in intelligent systems to support decision-making across various domains, such as healthcare, finance, and law enforcement. Despite their increasingly remarkable performance, the opacity of these models poses substantial challenges, particularly in the aspect of explainability. The Hugging Face Hub has become a pivotal repository for publicly available machine learning models, extensively reused in both academia and industry. This paper aims to address the imperative for explainability by analyzing the current state of inherent and non-augmented perceived explainability of machine learning models shared on the platform. By data mining the model registry and exploring the models' documentation, the models were categorized based on five common classes of machine learning algorithms discussed and empirically investigated from end-users' perspectives regarding explainability in existing works. Building on theoretical and user-centred empirical evidence from prior works focused on model performance and explainability, this work attempts to contextualize these two dimensions within the real-world distribution and popularity of models on the hub, thereby introducing a third dimension. Additionally, this work examines explainability through a three-tier categorization of models based on their explainability, i.e., non-, mediocrely-, and highly-explainable. The findings highlight the disproportionate prevalence of models built on deep neural networks, which are considered among the least explainable compared to those based on other classes of learning algorithms.</p>
      </abstract>
      <kwd-group>
        <kwd>eol&gt;Hugging Face</kwd>
        <kwd>model registry</kwd>
        <kwd>machine learning</kwd>
        <kwd>explainable artificial intelligence</kwd>
        <kwd>XAI</kwd>
        <kwd>explainability</kwd>
      </kwd-group>
    </article-meta>
  </front>
  <body>
    <sec id="sec-1">
      <title>1. Introduction</title>
      <p>
        In recent years, the rapidly increasing use of advanced machine learning (ML) models has significantly
enhanced the capabilities of various intelligent system applications to support decision-making across
multiple domains. Following the increased demand for accessible ML models and to facilitate their reuse,
the Hugging Face (HF) Hub has emerged as a pivotal repository of ML models [
        <xref ref-type="bibr" rid="ref1 ref2">1, 2</xref>
        ]. The models shared
via the platform are widely adopted and reused across academia and industry due to their versatility
and performance across a variety of tasks. Despite their remarkable performance, the opacity of these
models poses substantial challenges, particularly in the realm of explainability [
        <xref ref-type="bibr" rid="ref3">3</xref>
        ]. Explainability in
artificial intelligence (AI) is critical for ensuring transparency, trust, privacy awareness, and ethical
AI deployment [
        <xref ref-type="bibr" rid="ref4">4</xref>
        ]. It is not solely a technical concern; it is a multifaceted issue extending to legal,
ethical, and practical domains. For models to be reliable in sensitive applications such as healthcare,
education, employment, finance, and law enforcement, stakeholders must understand how and why
these models make specific decisions, recommendations, or actions [ 5]. Hence the recent interest in
explainable artificial intelligence (XAI). This necessity has also been highlighted in a recent wave of
legislative changes – the AI Act in the European Union [6] and a blueprint for the AI Bill of Rights in
the USA [7]. Both emphasize the importance of explainability and developing techniques to explain the
inner workings of ML models, such as those shared via the HF Hub.
      </p>
      <p>
        Existing work in XAI has explored the explainability of models based on various ML algorithms [
        <xref ref-type="bibr" rid="ref3 ref4">3, 4,
5, 8, 9</xref>
        ]. However, this has not been contextualized in terms of the distribution and popularity of publicly
shared ML models on leading platforms, such as the HF Hub. This work addresses the imperative for
explainability by analyzing the current state of end-user perceived explainability of ML models from the
HF Hub. To achieve this, all models shared via the HF Hub at the time of conducting the research, which
included more than 685k models, were obtained. Data mining was performed on the documentation
related to the models to categorize them into five common classes of ML algorithms [ 5]. While the
research community [10, 11, 12, 13] has mainly studied models from the HF Hub from the perspective of
reusing deep pretrained models, the platform is not limited to hosting deep learning models only. Despite
this, prior to conducting this research, we acknowledged that shallow ML models are less common.
Based on the obtained data, the models were evaluated from an explainability perspective with regard to
the employed class of ML algorithm and a three-tier categorization of model explainability, namely,
nonexplainable, mediocrely-explainable, and highly-explainable. Following prior work [
        <xref ref-type="bibr" rid="ref3 ref4">3, 4, 5, 8, 9</xref>
        ], models
were analyzed in terms of two dimensions – performance and explainability. Our work introduces
a third dimension, which considers the distribution and popularity of ML models in the real-world
landscape, captured through models from the HF Hub. Hence, the main contributions of this work lie in
the analysis of the distribution and popularity of the ML models shared on the HF Hub, contextualizing
explainability research in the real-world usage landscape, thereby enhancing the practical relevance of
XAI research.
      </p>
      <p>The rest of the paper is organized as follows. Section 2 provides an overview of the background
and related work relevant to this work. Section 3 details the research design utilized. The empirical
results obtained based on the defined research design are presented and discussed in Section 4. Finally,
Section 5 synthesizes the findings and addresses threats to validity.</p>
    </sec>
    <sec id="sec-2">
      <title>2. Background and Related Work</title>
      <sec id="sec-2-1">
        <title>2.1. Explainability of Machine Learning Models</title>
        <p>
          Explainability is related to the notion of explanation as an interface between a human – e.g., developer,
theorist, ethicist, or end-user – and the decision-maker – the ML model –, where the explanation is an
accurate approximation of the decision-maker and understandable to humans [5, 14]. The focus of this
work is solely on end-users, i.e., domain experts, who use and rely on decisions, recommendations, or
actions produced by a deployed intelligent system to assist their decision-making in work processes [
          <xref ref-type="bibr" rid="ref3">3, 5</xref>
          ].
As the focus of the explanation is on human understanding, empirical studies evaluate perceived
explainability, which can serve as a determinant of the efectiveness of an intelligent system; when
end-users can understand the behavior of the ML model used in an intelligent system, they are more
likely to trust and act on its decisions, especially when those difer from their own expectations [ 5, 15].
        </p>
        <p>
          In much existing XAI research, the explainability of individual ML models was conceptualized as a
trade-of between performance and inherent explainability [
          <xref ref-type="bibr" rid="ref3 ref4">3, 4, 8, 9</xref>
          ]. For instance, simple models based
on linear regressions were considered the most explainable, although they often do not perform as
well. Conversely, high-performing models, such as those based on deep learning, were considered less
explainable [
          <xref ref-type="bibr" rid="ref3">3, 8, 9</xref>
          ]. This initial view of the compromise between model performance and explainability
is commonly graphically depicted in a two-dimensional Cartesian coordinate system, as presented in
Figure 1 – subfigure A. Note that the coordinate axes are not quantified [ 16]. Theoretical contributions
assumed an increase in the performance of ML models based on diferent ML algorithms combined
with a continuous decrease in explainability; the relationship typically depicted as a linear or cubic
curve [5]. The notion of ordering ML models based on the explainability of the underlying ML algorithm
has been taken at face value for years, with little attempt at empirical confirmation. The first
usercentered empirical research to gather evidence on this notion was conducted by Herm et al. [5].
The authors evaluated the end-user perceived explainability of ML models based on five common
classes of ML algorithms, namely, linear regressions, decision trees, random forests, support vector
machines, and deep neural networks, without utilizing any XAI augmentations. It is important to note
that, although the research often refers to ensembles in general, we argue that it is more accurate to
specifically refer to random forests. The investigation was conducted exclusively on random forests
and due to the inherently interpretable nature of decision trees, their findings may not generalize to all
ensembles; thus, we opted for a more conservative approach to the naming of that class. The results
of the research led to an updated visualization, as depicted in Figure 1 – subfigure B. Based on these
ifndings, the authors grouped ML models based on explainability into three categories: no explainability
(deep neural networks), mediocre explainability (linear regressions, support vector machines), and high
explainability (decision trees, random forests), with the former encompassing deep, and the latter two
shallow models [5].
        </p>
      </sec>
      <sec id="sec-2-2">
        <title>2.2. The Hugging Face Hub</title>
        <p>
          General-purpose version-controlled hosting platforms, such as GitHub, ofer means for collaboration on
a common codebase and social interactions. The rise of ML led to the development of Git-based platforms
specialized for ML-based projects [17]. The HF Hub [
          <xref ref-type="bibr" rid="ref1">1</xref>
          ] is a centralized Git-based repository hosting
platform focused on ML-related content. It organizes its content into three registries: models (ML models
shared by the community), datasets (datasets of diferent modalities – text, images, audio – and domains),
and spaces (demonstrative interactive small-scale web applications) [
          <xref ref-type="bibr" rid="ref1">1</xref>
          ]. The platform is widely accepted
by the ML community. This is demonstrated by the inclusion of the BERT, T5, and Gemma models
shared by Google AI, the GPT-2 model shared by OpenAI, and the Llama model shared by Meta AI. Due
to its popularity and utilization in practice, HF Hub has been previously analyzed as a source of
stateof-the-art ML models, datasets, and projects. Previous works have focused on the reuse of pretrained
models shared on the HF Hub [10, 13, 12], their evolution and maintenance [
          <xref ref-type="bibr" rid="ref2">2</xref>
          ], vulnerabilities [18],
carbon footprints [19], and naming conventions [20]. Attempts to produce specialized solutions for
analyzing the HF Hub community have also been made [17].
        </p>
      </sec>
    </sec>
    <sec id="sec-3">
      <title>3. Research Design</title>
      <sec id="sec-3-1">
        <title>3.1. Research Goal and Questions</title>
        <p>
          Following the works of Castaño et al. [
          <xref ref-type="bibr" rid="ref2">2, 19</xref>
          ], a structured approach to defining research goals and
questions based on the Goal-Question-Metric (GQM) methodology was employed. The primary research
goal of this work was defined as to analyze and evaluate ML models shared on the HF Hub to investigate
the current state of perceived explainability from the perspective of end-users with regard to the distribution
and popularity of these models across various common classes of ML algorithms. To address this, two
research questions (RQs) guided the research:
RQ1. What is the distribution of diferent common classes of ML algorithms used in models shared on the
        </p>
        <p>HF Hub, and how does it relate to explainability?
RQ2. What is the distribution of diferent common classes of ML algorithms used in models shared on the</p>
        <p>HF Hub with regard to their popularity, and how does it relate to explainability?</p>
      </sec>
      <sec id="sec-3-2">
        <title>3.2. Data Mining Research</title>
        <p>To address the research goal, a data mining research was conducted in three stages, namely data
collection and preparation, categorization validation, and data analysis. An overview of the process is
presented in Figure 2, and further discussed in the following subsections.</p>
        <sec id="sec-3-2-1">
          <title>3.2.1. Data Collection and Preparation</title>
          <p>In the data collection and preparation stage, first, a comprehensive list of models available on the HF
Hub was retreived using the HF API [21]. This retrieval was performed through the HfApi class and its
list_models() function. For each model, the following data attributes were collected: model_name
(the model’s name), tags (the list of tags associated with the model), created_at (the creation date
of the model’s repository on the HF Hub), and downloads (the number of model’s downloads in the
last 30 days). Note that the earliest creation date recorded is March 2, 2022, 23:29:04 GMT, marking the
start of HF Hub’s creation date storage. Data collection was conducted on May 30th, 2024, resulting in a
dataset of 685,321 models.</p>
          <p>Since the specific ML algorithms used for each model are not directly reported, a lexical
keywordbased model was employed to categorize each model based on its documentation (i.e., name and tags)
into five common classes of ML algorithms as discussed by Herm et al. [ 5]. Initially, names and tags were
converted to lowercase, and special characters (e.g., dashes, underscores) and whitespaces were removed.
A regular expression approach was then used to match words in names or tags against predefined
keywords related to each class. This approach is supported by previous findings by Jiang et al. [ 20],
who demonstrated that model architectures could often be inferred from their names due to naming
conventions on the HF Hub; in a sample of 300 randomly selected models from the HF Hub, 59% included
information about their architecture in their names. To develop the predefined set of keywords, the first
author conducted several iterations of keyword selection and validation, based on frequency analysis of
n-grams of initial names and tags, as well as heuristics from existing body-of-knowledge. For instance,
keywords for deep neural networks were also derived with the help from HF Hub documentation [22].
Models of unknown class of ML algorithms or based on ML algorithms not represented in five observed
classes were categorized as “Unknown”. The set of keywords used for model categorization is presented
in Table 1. Using the obtained list of models and the keyword-based categorization model, 414,304
models (60.45%) were categorized.
linearregression, linreg, linearreg
decisiontree, dtree, dectree
supportvectormachine, supportvector, svmachine, svm
randomforest, randomforestregressor, randomforestclassifier, randomizedforest, rfregressor,
rfclassifier
deepneuralnetwork, dnn, neuralnetwork, deeplearning, bert, llama, gpt, electra, longformer,
nlp, transformer, deepnn, deepnet, transformers, albert, align, altclip,
audiospectrogramtransformer, autoformer, bark, bart, beit, bertgeneration, bigbird, bigbirdpegasus, biogpt,
bit, blenderbot, blenderbotsmall, blip, blip2, bloom, bridgetower, bros, camembert,
canine, chineseclip, chineseclipvisionmodel, clap, clip, clipvisionmodel, clipseg, clvp,
codellama, codegen, cohere, conditionaldetr, convbert, convnext, convnextv2, cpmant, ctrl, cvt,
data2vecaudio, data2vectext, data2vecvision, dbrx, deberta, debertav2, decisiontransformer,
deformabledetr, deit, depthanything, deta, detr, dinat, dinov2, distilbert, donutswin, dpr,
dpt, eficientformer, eficientnet, encodec, encoderdecoder, ernie, erniem, esm, falcon,
fastspeech2conformer, flauert, flava, fnet, focalnet, fsmt, funnel, fuyu, gemma, git, glpn, gptsw3,
gpt2, gptbigcode, gptneo, gptneox, gptneoxjapanese, gptj, gptsanjapanese, graphormer,
groundingdino, groupvit, hubert, ibert, idefics, idefics2, imagegpt, informer, instructblip,
jamba, jetmoe, jukebox, kosmos2, layoutlm, layoutlmv2, layoutlmv3, led, levit, lilt, llava,
llavanext, longformer, longt5, luke, lxmert, m2m100, mamba, marian, markuplm, mask2former,
maskformer, maskformerswin, mbart, mctct, mega, megatronbert, mgpstr, mistral, mixtral,
mobilebert, mobilenetv1, mobilenetv2, mobilevit, mobilevitv2, mpnet, mpt, mra, mt5,
musicgen, musicgenmelody, mvp, nat, nezha, nllbmoe, nougat, nystromformer, olmo, oneformer,
openllama, openaigpt, opt, owlv2, owlvit, paligemma, patchtsmixer, patchtst, pegasus,
pegasusx, perceiver, persimmon, phi, phi3, pix2struct, plbart, poolformer, pop2piano,
prophetnet, pvt, pvtv2, qdqbert, qwen2, qwen2moe, rag, realm, recurrentgemma, reformer, regnet,
rembert, resnet, retribert, roberta, robertaprelayernorm, rocbert, roformer, rwkv, sam,
seamlessm4t, seamlessm4tv2, segformer, seggpt, sew, sewd, siglip, siglipvisionmodel,
speechencoderdecoder, speechtotext, speechtotext2, speecht5, splinter, squeezebert, stablelm,
starcoder2, superpoint, swiftformer, swin, swin2sr, swinv2, switchtransformers, t5,
tabletransformer, tapas, timeseriestransformer, timesformer, timmbackbone, trajectorytransformer,
transfoxl, trocr, tvlt, tvp, udop, umt5, unispeech, unispeechsat, univnet, upernet, van,
videollava, videomae, vilt, vipllava, visionencoderdecoder, visiontextdualencoder,
visualbert, vit, vithybrid, vitmae, vitmsn, vitdet, vitmatte, vits, vivit, wav2vec2, wav2vec2bert,
wav2vec2conformer, wavlm, whisper, xclip, xglm, xlm, xlmprophetnet, xlmroberta,
xlmrobertaxl, xlnet, xmod, yolos, yoso</p>
        </sec>
        <sec id="sec-3-2-2">
          <title>3.2.2. Categorization Validation</title>
          <p>To validate the approach to model categorization and determine the error rate, a manual categorization
of a sample of the models was performed. To determine the sample size, Cochran’s sample size formula
was considered, formally defined as:
where 0 is the sample size,  is the selected Z-score corresponding to the desired confidence level (e.g.,
1.96 for a 95% confidence level),  is the estimated proportion of an attribute present in the population,
and  is the desired level of precision (i.e., margin of error) [23]. When dealing with a finite population,
the formula can be adjusted as:
0 =
 2 ·  · (1 − )</p>
          <p>2
 =</p>
          <p>0
1 + 0− 1

where  is the size of the population, 0 is the initial Cochran’s sample size recommendation, as
defined in Equation 1, and  is the adjusted sample size for a finite population [ 23]. The validation was
conducted on a sample size of  = 384. Due to the acknowledged unbalanced nature of classes in HF
Hub (favoring deep learning models), stratified sampling was utilized to extend the validation to four
less-represented classes, increasing the sample size to  = 482.</p>
          <p>Based on the obtained sample size, the first author manually categorized the models into five classes
of ML algorithms and an additional “Unknown” class. For the categorization of each model in the
(1)
(2)
sample, the human annotator thoroughly reviewed the entire model documentation beyond the model
name and tags, including the model card and, where available, the source code. The comparison
between predicted classes by the automated categorization model and manually categorized classes
is presented in Figure 3 in the form of a confusion matrix. It highlights the automated approach’s
adequate prediction ability. There are some miscategorizations between the “Deep Neural Networks”
and “Unknown” classes, most can be attributed to additional data (i.e., model card and codebase) that
the manual annotator had access to. Many miscategorizations related to the “Support Vector Machines”
class were also attributed to models with long randomized name strings, which sometimes included
svm abbreviations. To measure inter-annotator agreement between manual and automated model
categorization, Cohen’s Kappa ( ) was computed, which yield  = 0.867, indicating an Almost perfect
level of agreement (with the threshold for Almost perfect being  = 0.820 per [24]).</p>
        </sec>
        <sec id="sec-3-2-3">
          <title>3.2.3. Metrics and Data Analysis</title>
          <p>In the context of RQ1, the raw count of models for each class of ML algorithms was used. In the context
of RQ2, the popularity of each class was estimated via the proxy of the number of downloads, as used
in prior work [12]. This was done by multiplying the number of models associated with each class by
their respective download counts.</p>
        </sec>
      </sec>
    </sec>
    <sec id="sec-4">
      <title>4. Results and Discussion</title>
      <p>The results of the categorization based on five common classes of learning algorithms are presented
in Table 2. It can be observed that models utilizing deep neural networks represent the vast majority
(~99.9%). Decision tree-based ( = 13) and linear regression-based models ( = 18) were published
exceptionally rarely on the HF Hub platform. A graphical visualization depicting the trade-of between
model performance and explainability in the context of model distribution on the HF Hub is presented
in Figure 4 – subfigure A. To enhance readability, we represented the results using the size of the circles
to indicate the model count instead of using a three-dimensional Cartesian coordinate system. The
ifgure highlights the disproportionate frequency of models built on deep neural networks compared to
all other observed algorithms. Furthermore, when accounting for the popularity of models, the disparity
becomes even more apparent, as observed in Figure 4 – subfigure B.</p>
      <p>The results of the categorization, considering a three-tier classification of models based on their
explainability, are presented in Table 3. It can be observed that models with no inherent explainability,
as perceived by end-users, represent the vast majority (~99.9%), followed by models with mediocre
explainability, and lastly, models with high explainability. An insight into the creation time of the
models hosted on the HF Hub, presented in Figure 5, further illustrates the ongoing trend of prevalent
deep neural network models with no inherent explainability over the months. Note that only models
created after March 2022, the month when the HF Hub began storing model repository creation dates,
are included in the figure. Additionally, for better readability, the values on the y-axis are displayed on
a symmetric logarithmic scale.</p>
      <p>
        In the context of RQ1, we observe that ML models based on deep neural networks, which ofer no
inherent explainability, prevail on the HF Hub over shallow ML models. This indicates that models
might prioritize performance over explainability. This trend is even more apparent when considering
their popularity (RQ2). However, as discussed in [
        <xref ref-type="bibr" rid="ref4">4, 5, 16</xref>
        ], it is important to emphasize that this is
merely a general observation, as ordering ML models based on their underlying algorithm is hardly
deterministic. More complex models do not necessarily achieve better performance, especially in
domains with well-structured data, low data complexity, and limited data availability. Despite this,
the dominance of deep neural network-based models and their predominantly black-box nature poses
significant challenges in understanding and interpreting model decisions. This raises important user
considerations, particularly in domains where transparency and accountability are crucial. Currently,
challenges related to explaining deep neural network models are mostly associated with their model-free
architecture and often lack adequate explanations of their full architecture (i.e., global explanations, as
most approaches are local or visual, focused on a single instance at a time). Available global explanation
methods are also computationally expensive due to the high number of features and parameters in the
deep architectures of neural networks. Approximation models (created with methods such as LIME) for
deep neural networks might closely resemble the black-box model for one dataset subset, while for other
subsets, they might deviate significantly. Additionally, no global explanation method for text-based
datasets can explain the rationale of deep neural network models [25]. Without adequate explanations
of model behavior, users may hesitate to trust these models in critical applications. These challenges
are compounded by the clear prevalence of deep neural network-based models on platforms like HF
Hub. However, by acknowledging this trade-of and focusing on the development of explainability
techniques tailored for deep neural networks, such as layer-wise relevance propagation and attention
mechanisms, the research community can work towards reducing the disparity between performance
and explainability. This will ultimately advance the responsible adoption of deep learning models in
real-world scenarios. This agenda also aligns with DARPA’s anticipation [
        <xref ref-type="bibr" rid="ref3">3</xref>
        ] of improvements in the
explainability (and performance) of future techniques compared to the current state-of-the-art.
      </p>
    </sec>
    <sec id="sec-5">
      <title>5. Conclusions</title>
      <p>
        This paper addresses the explainability of ML models in real-world usage by analyzing data from the
HF Hub platform. It evaluates shared models and their underlying ML algorithms concerning inherent
end-user perceived explainability. Building on prior works [
        <xref ref-type="bibr" rid="ref3 ref4">3, 4, 5, 8, 9</xref>
        ], this work examines five
classes of ML algorithms and a three-tier categorization of model explainability. The findings reveal
a significant imbalance, with deep neural network-based models, which lack inherent explainability,
dominating the platform. We highlight the need for future work, which should build on enhancing
understanding of perceived explainability (as a trade-of to performance) beyond the five observed
algorithm classes, ideally providing further insights into various deep neural network-based models and
aligning algorithm categorization with ML field. Future work should also address further development
of augmented XAI techniques specifically for deep neural network-based models, in line with their
extensive usage and popularity, to ensure their transparent application across various domains.
      </p>
      <sec id="sec-5-1">
        <title>5.1. Limitations and Threats to Validity</title>
        <p>
          The data may contain inaccuracies, as ML algorithms employed are not explicitly defined for each model
on the HF Hub, limiting our analysis to models with identifiable ML algorithm classes and introducing
selection bias. The automated model categorization relied solely on model names and tags. Future
studies might expand to other model documentation, e.g., model cards (though it should be noted
that recent research reported that only half of the models have model cards [13]), and codebases. To
assess the automated categorization approach, we performed manual validation on a sample of models,
showing a small percentage of miscategorization and almost perfect agreement. We focused on five
classes of ML algorithms for which end-user perceived explainability has been empirically analyzed by
Herm et al. [5], potentially overlooking other relevant algorithms. It is essential to acknowledge the
categorization used in the XAI field, and thus in [ 5], is not aligned with other common categorizations
in the ML domain [26]. However, it was followed due to its common references in XAI literature.
Additionally, some classes are narrow (e.g., linear regressions), while others are broader (e.g., deep
neural networks). Relying solely on empirical evidence from this research increases the risk to the
validity of our results, as data might not account for variability in explainability across diferent datasets,
domains, and performance measures, as the research was conducted considering only two datasets
(one with low data complexity, i.e., tabular dataset, and one with high data complexity, i.e., image
dataset) from the healthcare sector, and considered performance in terms of accuracy. It should also be
considered that the research focused solely on inherent explainability without considering additional
post-hoc XAI augmentations. For measuring popularity, we used the number of downloads, a proxy
used in prior work to indicate usage concentration [12]. However, future work might consider other
measures, e.g., the number of likes and downstream reuse. Furthermore, the model registry from the
HF Hub platform may not necessarily represent what is used to address real-world problems in general;
it should be considered that the platform hosts predominantly pretrained models focused on natural
language processing tasks [19]. Additionally, the results cannot be generalized to other ML model hubs,
such as ONNX Model Zoo and PyTorch Hub. Though the results still serve as a trend indicator of ML
models shared within the HF Hub community. The models were collected in May 2024; hence, the
results might not align with future platform developments, especially due to rapid increases in shared
models. This can be demonstrated by significant diferences in available models in related works; a
research carried out in February 2023 obtained around 110k models [18], in March 2023 170k models
[19], and in November 2023 380k models [
          <xref ref-type="bibr" rid="ref2">2</xref>
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