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  <front>
    <journal-meta>
      <issn pub-type="ppub">1613-0073</issn>
    </journal-meta>
    <article-meta>
      <title-group>
        <article-title>The Future of Continual Learning in the Era of Foundation Models: Three Key Directions</article-title>
      </title-group>
      <contrib-group>
        <contrib contrib-type="author">
          <string-name>Jack Bell</string-name>
          <email>jack.bell@di.unipi.it</email>
          <xref ref-type="aff" rid="aff0">0</xref>
        </contrib>
        <contrib contrib-type="author">
          <string-name>Luigi Quarantiello</string-name>
          <email>luigi.quarantiello@phd.unipi.it</email>
          <xref ref-type="aff" rid="aff0">0</xref>
        </contrib>
        <contrib contrib-type="author">
          <string-name>Eric Nuertey Coleman</string-name>
          <email>eric.coleman@phd.unipi.it</email>
          <xref ref-type="aff" rid="aff0">0</xref>
        </contrib>
        <contrib contrib-type="author">
          <string-name>Lanpei Li</string-name>
          <email>lanpei.li@isti.cnr.it</email>
          <xref ref-type="aff" rid="aff0">0</xref>
          <xref ref-type="aff" rid="aff1">1</xref>
        </contrib>
        <contrib contrib-type="author">
          <string-name>Malio Li</string-name>
          <email>malio.li@phd.unipi.it</email>
          <xref ref-type="aff" rid="aff0">0</xref>
        </contrib>
        <contrib contrib-type="author">
          <string-name>Mauro Madeddu</string-name>
          <email>mauro.madeddu@phd.unipi.it</email>
          <xref ref-type="aff" rid="aff0">0</xref>
        </contrib>
        <contrib contrib-type="author">
          <string-name>Elia Piccoli</string-name>
          <email>elia.piccoli@phd.unipi.it</email>
          <xref ref-type="aff" rid="aff0">0</xref>
        </contrib>
        <contrib contrib-type="author">
          <string-name>Vincenzo Lomonaco</string-name>
          <email>vincenzo.lomonaco@unipi.it</email>
          <xref ref-type="aff" rid="aff0">0</xref>
        </contrib>
        <contrib contrib-type="author">
          <string-name>Workshop</string-name>
        </contrib>
        <contrib contrib-type="editor">
          <string-name>Continual Learning, Foundation Models, Continual Pre-training, Continual Fine-tuning, Continual Composition-</string-name>
        </contrib>
        <aff id="aff0">
          <label>0</label>
          <institution>Department of Computer Science, Università di Pisa</institution>
          ,
          <addr-line>56126 Pisa</addr-line>
          ,
          <country country="IT">Italy</country>
        </aff>
        <aff id="aff1">
          <label>1</label>
          <institution>Institute of Information Science and Technologies, National Research Council</institution>
          ,
          <addr-line>56124 Pisa</addr-line>
          ,
          <country country="IT">Italy</country>
        </aff>
      </contrib-group>
      <pub-date>
        <year>2025</year>
      </pub-date>
      <abstract>
        <p>Continual learning-the ability to acquire, retain, and refine knowledge over time-has always been fundamental to intelligence, both human and artificial. Historically, diferent AI paradigms have acknowledged this need, albeit with varying priorities: early expert and production systems focused on incremental knowledge consolidation, while reinforcement learning emphasised dynamic adaptation. With the rise of deep learning, deep continual learning has primarily focused on learning robust and reusable representations over time to solve sequences of increasingly complex tasks. However, the emergence of Large Language Models (LLMs) and foundation models has raised the question: Do we still need continual learning when centralised, monolithic models can tackle diverse tasks with access to internet-scale knowledge? We argue that continual learning remains essential for three key reasons: (i) continual pre-training is still currently necessary to ensure foundation models remain up to date, mitigating knowledge staleness and distribution shifts while eficiently integrating new information; (ii) continual fine-tuning enables models to specialise and personalise eficiently, adapting to domain-specific tasks, user preferences, and real-world constraints without full retraining, avoiding the need for computationally expensive long context-windows; (iii) continual compositionality ofers a scalable and modular approach to intelligence, enabling the orchestration of foundation models and agents to be dynamically composed, recombined, and adapted in an open-ended way. While continual pre-training and fine-tuning are currently explored as niche research directions, we argue it is continual compositionality that will mark the re-birth of continual learning. The future of AI will not be defined by a single static model but by an ecosystem of continually evolving and interacting models, making continual learning more relevant than ever.</p>
      </abstract>
      <kwd-group>
        <kwd>ality</kwd>
      </kwd-group>
    </article-meta>
  </front>
  <body>
    <sec id="sec-1">
      <title>1. Introduction</title>
      <p>
        In recent years, artificial intelligence (AI) systems have begun to surpass human performance in many
domains such as natural language processing (NLP) and computer vision. However, these models
are typically static in nature and do not naturally update their understanding as new data emerges
over time. In contrast, humans tend to approach problems as sequential learning tasks, building on
past information without forgetting previously learned knowledge or requiring rehearsal to retain it
[
        <xref ref-type="bibr" rid="ref1">1</xref>
        ]. Both human and AI systems require the ability to learn and adapt continuously, whilst avoiding
so-called catastrophic forgetting, in which new learning erases previous knowledge. Addressing this
challenge is one of the core aims of Continual Learning (CL).
      </p>
      <p>Continual Learning research therefore revolves around two primary goals: adaptation and memory
consolidation. Adaptation emphasises rapid responsiveness, enabling an agent to quickly adjust</p>
      <p>CEUR</p>
      <p>
        ceur-ws.org
its behaviour or representations to maximise a utility function given the current task, situation or
environment [
        <xref ref-type="bibr" rid="ref2">2</xref>
        ]. Memory consolidation, on the other hand, involves building durable, generalisable
knowledge and skills from past experiences deemed relevant to future tasks. This consolidation goes
beyond mere retention; it focuses on developing abstract and hierarchical representations of knowledge,
reusable across increasingly complex tasks over time.
      </p>
      <p>
        Historically, these two goals have been addressed with varying degrees of importance in diferent
research methodologies, contexts and communities. Early expert systems, for instance, focused on
consolidating incremental domain knowledge, yet lacked flexibility in rapidly adapting to new information
without significant manual efort. Reinforcement learning (RL) methods, such as CHILD, introduced
by Ring [
        <xref ref-type="bibr" rid="ref3">3</xref>
        ], aimed instead at quick progressive learning, tackling easier tasks before addressing more
complex ones, and adapting in a general approach towards continual reinforcement learning.
Subsequent work on low-dimensional streaming data looked to address the issue of learning concept drifts
[
        <xref ref-type="bibr" rid="ref2">2</xref>
        ], similarly focusing on rapid adaptation. With the steep rise and success of deep learning around
2012, the focus shifted prominently towards memory consolidation and generalisation. Deep continual
learning leveraged neural networks to learn hierarchical, abstract representations directly from data,
enabling the efective reuse of these representations across new tasks [
        <xref ref-type="bibr" rid="ref4 ref5">4, 5</xref>
        ]. Here, consolidation is not
simply memory retention but involves the generalisation of latent knowledge and skills that facilitate
adaptation to novel scenarios. We further explore the history of continual learning and its evolution to
where it is today in section 2.
      </p>
      <p>
        More recently, the emergence of LLMs has changed the focus of AI research towards
transformerbased models with less focus on ’traditional’ Machine Learning (ML). These models, pre-trained on
vast datasets, have demonstrated remarkable capabilities to learn rich generalisations of the world
[
        <xref ref-type="bibr" rid="ref6">6</xref>
        ], performing well across a range of tasks. Combining these impressive capabilities, a demonstrated
reduced propensity for catastrophic forgetting [
        <xref ref-type="bibr" rid="ref7">7</xref>
        ] and access to the internet-scale knowledge, it is
tempting to ask: Is continual learning still necessary within the era of foundation models?
      </p>
      <p>Applying continual learning, with its two main aims of adaptability and memory consolidation, to
Foundation Models (FMs) is a way to overcome some of their inherent shortcomings: since a FM’s
parameters are fixed at deployment, every model can be seen as a snapshot of the world at the point of
training. Practical use of FMs demands post-training adaptation, through fine-tuning or personalisation
for a downstream task. Therefore, their static nature poses a significant challenge — they lack the
intrinsic adaptability required to stay current in rapidly changing environments.</p>
      <p>
        So far, FM-based agents that actively interact with their environment have been proposed as a
promising solution, leveraging continual adaptation to progressively improve capabilities [
        <xref ref-type="bibr" rid="ref8">8</xref>
        ]. However,
the ability to adapt to new tasks is not enough; it is instead necessary to consolidate new knowledge
over time to improve the overall understanding of the world. Challenges such as distributional shifts,
long task sequences, task heterogeneity and inaccessible upstream data [
        <xref ref-type="bibr" rid="ref9">9</xref>
        ] necessitate a renewed
focus on continual learning. Shi et al. [
        <xref ref-type="bibr" rid="ref9">9</xref>
        ] further observe that these hurdles have pushed recent work
toward task-incremental and domain-incremental benchmarks, where the task identity is supplied or
irrelevant. Consequently, while such settings simplify experimentation for academic settings, real-world
deployments still confront class-incremental conditions in which entirely new tasks must be detected
and learned on the fly [
        <xref ref-type="bibr" rid="ref10">10</xref>
        ]. We further detail the need for CL in foundation models in section 3.
      </p>
      <p>
        Given this context, CL for foundational models is developing along three directions: Continual
Pre-Training (CPT), Continual Fine-Tuning (CFT) and Continual Compositionality &amp;
Orchestration (CCO). Human perception provides an instructive analogy: during infancy, critical periods
enable rapid specialisation and consolidation of broad sensory capabilities such as vision and language
discrimination [
        <xref ref-type="bibr" rid="ref11">11</xref>
        ]. Similarly, in ML, extensive pre-training ideally establishes a general-purpose
foundational model, but CPT still remains practically necessary. Continual fine-tuning, in turn, allows
eficient specialisation and personalisation to specific downstream tasks or contexts. However, both
CPT and CFT typically require relatively lower-frequency adaptation cycles. Furthermore, their reliance
on large-scale datasets, substantial computational resources and incremental improvement constraints
due to scaling laws limits their potential to drive substantial advances alone [
        <xref ref-type="bibr" rid="ref9">9</xref>
        ], particularly as these
approaches predominantly extend established capabilities rather than enabling fundamentally new
behaviours. However, recent work on test-time scaling laws demonstrates that, once model size passes
a certain threshold, allocating additional inference-time compute delivers larger accuracy gains than
further parameter growth [
        <xref ref-type="bibr" rid="ref12">12</xref>
        ]. Parallel advances in multi-step chain-of-thought prompting and in
multi-agent frameworks, where several specialised LLMs negotiate, critique, or divide labour, likewise
point to performance improvements that arise from coordination rather than monolithic scale [
        <xref ref-type="bibr" rid="ref13 ref14">13, 14</xref>
        ].
Together, these trends expose the practical limits of an end-to-end foundation model and highlight the
need for a modular, dynamically reconfigurable approach.
      </p>
      <p>
        We therefore contend that Continual Compositionality and Orchestration represents the most
promising and necessary direction for future continual learning research. Unlike CPT and CFT, CCO
inherently supports high-frequency adaptation, allowing dynamic orchestration, recombination and
collaborative interaction among multiple FMs or agents. Recent advances in FMs have primarily emerged
not from additional computational resources, but rather through enhanced reasoning abilities [
        <xref ref-type="bibr" rid="ref15">15</xref>
        ] and
longer context windows [
        <xref ref-type="bibr" rid="ref16">16</xref>
        ], both of which are forms of orchestration rather than scale. Consequently,
the future of continual learning likely resides in decentralised ecosystems, where multiple adaptive
agents continuously interact, evolve and collaboratively address increasingly complex problems. This
paradigm exhibits parallels to society as a whole, where collections of diferent individuals can come
together to solve dificult tasks. Taken from a large enough intelligent population, a random sample of
people will outperform a sample of the best performing agents — with the intuition being that diversity
is more important than individual ability [
        <xref ref-type="bibr" rid="ref17">17</xref>
        ]. In a similar vein, a diverse subset of agents may well be
more adept at problem solving than a sample of the best performing agents at a given task.
      </p>
      <p>In this paper, we first review Continual Pre-Training ( 4.1), which equips large-scale foundational
models with adaptive, resource-eficient mechanisms to incorporate new knowledge without
catastrophic forgetting. We then examine Continual Fine-Tuning (4.2), enabling precise specialisation to
downstream tasks while retaining broad, generalisable representations. Finally, we argue that Continual
Compositionality &amp; Orchestration (4.3) - with its high-frequency, modular coordination of specialised
agents - ofers the most promising path forward. By moving from monolithic snapshots to dynamic,
decentralised ecosystems of models, CCO can drive the next wave of resilient, scalable, and sustainable
AI systems.</p>
    </sec>
    <sec id="sec-2">
      <title>2. Background and Related Work</title>
      <p>The rise of Deep Learning (DL) in 2012 marked a pivotal moment for the entire ML research community.
Initial eforts in this domain concentrated on utilising deep neural networks for representation learning,
allowing models to capture abstract and hierarchical features from data. Nevertheless, when trained
sequentially on multiple tasks, these models remained susceptible to catastrophic forgetting. This
highlights the need for CL, which has had a large impact on the broader field of ML.</p>
      <p>
        A widely used definition, often taken to specify Deep Continual Learning, is ofered by Lesort et al.
[
        <xref ref-type="bibr" rid="ref18">18</xref>
        ]. They describe continual learning as a learning paradigm where a model learns from a continuous
stream of data, adapting to new information while preserving previously acquired knowledge. This
definition emphasises the importance of both stability and plasticity in the learning process, where
there is an important trade-of between retaining past knowledge and being plastic enough to adapt to
new data or domains. The objective of CL is to have a machine learning model that can be adapted
quickly to shifts in data distribution or “tasks”, enabling it to retain already acquired knowledge and
concepts and reuse these representations to facilitate better learning across new tasks.
      </p>
      <p>This is a key diference between CL and traditional machine learning approaches, which typically
require retraining on a static dataset to incorporate new information.</p>
      <p>Early studies focused on the problem of catastrophic forgetting in neural networks [19, 20], where
authors discovered the degradation of model performance on previous tasks while learning a new one.
To overcome the issue, diferent basic approaches were proposed [ 21, 22, 23, 24]. These early works
laid the foundations for more sophisticated approaches that emerged in the following years. The main
approaches within CL can be categorised into three main schools of thought: regularisation-based
methods, dynamic architectures, and memory-based techniques [25, 26].</p>
      <p>Regularisation-based methods aim to mitigate catastrophic forgetting by adding constraints to
the learning process, ensuring that important weights from previous tasks or domains are preserved.
EWC [24] adds a regularisation term to the loss function to preserve important weights from previous
tasks; SI [27] uses a similar approach but focuses on the Fisher information matrix to identify important
weights; LWF [23] introduces a distillation loss to retain knowledge from previous tasks.
Dynamic architectures involve modifying the model’s structure to accommodate new tasks while
retaining previously learned knowledge. PNNs [28] add new subnetworks for each task while keeping
the previously learned parameters frozen; LWTA [21] divides the networks into diferent blocks and the
forward propagation is done only by local winner weights; PackNet [29] prunes the networks and uses
masks to filter weights for diferent tasks; Piggyback [ 30] drops the weights training [31] and focuses
only on weights masking; a similar approach is used in HAT [32], but masking the units instead of the
weights; SupSup [33] simplifies this even more using only a seed to generate random weights and a
weighted sum of masks.</p>
      <p>Memory-based methods utilise stored examples from past tasks to reinforce prior knowledge during
training. GDumb [34] randomly selects a subset of exemplars from previous tasks and uses them to
train the model; GEM [35] uses episodic memory to store exemplars from previous tasks and ensure
that the model does not forget them during training; iCaRL [36] utilises stored examples from past
tasks to replay and reinforce prior knowledge during training; potentially, one could also use latent
generative replay to generate new samples from the previous tasks [37, 38].</p>
      <p>For a clearer academic evaluation of diferent CL methods, three main scenarios have been defined and
are widely used within the community [39]. In Task-incremental learning, the aim is to incrementally
learn a set of distinct tasks based on a given task-id. Whereas in Domain-incremental learning, the
context or input distribution varies over time, whilst the task remains constant (e.g. learning to drive in
diferent weather conditions). Finally, in Class-incremental learning, the aim is to incrementally
learn to discriminate between a growing number of objects or classes, where task identification is also
required. This last scenario is naturally the most dificult to solve, as well as the most applicable within
real-world scenarios.</p>
      <p>Diferently from CL models, Foundation Models (FM) are characterised by their large scale,
pretraining on huge amounts of data, and ability to perform a wide range of tasks with a relatively small
amount of fine-tuning. These models, such as BERT [ 40], GPT-3 [41], and CLIP [42], have demonstrated
remarkable performance across various benchmarks and applications. However, one of the biggest
problems faced by FM models is homogenisation [43], where a single unified model trained on diverse
data results in generalised internal knowledge representations. While this approach enables model
transfer across tasks, it also averages out critical domain-specific nuances, leading to inherent biases
from the most dominant data sources.</p>
      <p>More generally speaking, a monolithic AI system, which is a single large model that is trained on a
wide range of tasks and domains [44], is typically pre-trained on massive datasets and then fine-tuned for
specific tasks. Such models often require extensive computational resources for training and inference,
making them less accessible for smaller organisations and researchers. Additionally, a monolithic model
can sufer from knowledge staleness, where the model’s performance degrades over time as new data
becomes available. Furthermore, their centralised nature poses risks related to single points of failure
making them less robust in critical applications.</p>
      <p>On the other hand, continual learning ofers a more sustainable and adaptive alternative by enabling
models to learn incrementally, adapt to new tasks, and operate eficiently in dynamic settings [ 25]. This
paradigm shift is essential for addressing the limitations of monolithic AI and fostering more equitable
and resilient AI systems. Continual learning methods could benefit FMs in particular by enabling them
to adapt to new tasks and domains without requiring extensive retraining [45], thereby improving their
performance over time. By incorporating continual learning strategies, FMs can mitigate issues such as
knowledge staleness and ineficiency in adaptation. Furthermore, these methods can help reduce the
social and environmental impact of FMs by minimising the need for large-scale retraining, which often
requires significant computational resources and energy consumption.</p>
    </sec>
    <sec id="sec-3">
      <title>3. The Need for Continual Learning in the Foundation Model Era</title>
      <p>Recently, it has been shown that foundational models such as LLMs have the ability to both “reason”
and generalise through the use of techniques such as chain of thought (CoT) prompting, by breaking a
complex problem into a series of intermediate steps [46]. This trend of utilising the zero-shot capabilities
of LLMs, perhaps with the addition of prompt engineering and later downstream-task fine-tuning,
is, however, subject to many diferent limitations such as the brittleness and inconsistency of the
generalised reasoning steps.</p>
      <p>
        Foundation models such as GPT-3, BERT and DALL-E can quickly become outdated as the real-world
data they are trained on changes [41, 43]. This leads to model staleness over time, where often full
model retraining is the only solution used to mitigate this. Recent estimates indicate that the cost
of training models of a scale comparable to GPT-4.5 or similar architectures likely reached tens of
millions of dollars due to the enormous compute and energy resources required [47]. Beyond the
economic impact, the energy required for such massive compute workloads translates into significant
environmental impacts. Studies by Schwartz et al. [
        <xref ref-type="bibr" rid="ref19">48</xref>
        ] and Strubell et al. [
        <xref ref-type="bibr" rid="ref20">49</xref>
        ] indicate that the high
energy consumption involved in training these models contributes substantially to carbon emissions,
emphasising the need for more sustainable approaches.
      </p>
      <p>
        State of the art large scale models are typically trained on vast, diverse datasets to capture a wide range
of linguistic patterns and knowledge. Whilst this training approach enables impressive generalisation
across tasks, it results in a system that is too general to properly address the requirements of individual
users or specialised domains [
        <xref ref-type="bibr" rid="ref21">50</xref>
        ]. In scenarios such as personalised recommendations or adaptive
customer support, tailoring interactions based on a user’s context or preferences is of paramount
importance; however, static models tend to produce generic outputs even after fine-tuning.
      </p>
      <p>
        Further, conventional personalisation methods, relying on post-training adjustments or Test Time
Training (TTT) face significant challenges. In TTT or test time adaptation (TTA), a model adjusts its
parameters during inference based on the current input or an auxiliary task, aiming to better align
with the data distribution at test time [
        <xref ref-type="bibr" rid="ref22">51</xref>
        ]. Whilst this method allows for on-the-fly adaptation, it
frequently requires additional compute post-deployment and may struggle to capture long-term user
preferences. Additionally, TTT needs to be combined with continual adaptation with care as it can
interfere with pre-trained representations if not done correctly, leading to instability and ultimately
catastrophic forgetting.
      </p>
      <p>
        The rising computational and financial demands for training state of the art models have led to a
concentration of resources within a small number of organisations. This centralisation means that only
a few giants of industry possess the capability to develop, maintain, and update foundation models
at scale [
        <xref ref-type="bibr" rid="ref23">52</xref>
        ]. As a result, there is an inherent risk of monopolisation, where control over advanced
AI technologies is restricted to those with the resources, potentially limiting progress and diversity
within research, raising wider issues around transparency and accountability. For instance, when
few entities dominate model training and deployment, issues such as biased data representation and
the under-representation of marginalised groups can become more pronounced [
        <xref ref-type="bibr" rid="ref24">53</xref>
        ]. Additionally,
the centralised model may raise the barrier to entry for smaller research teams, universities, and
independent developers, inadvertently slowing innovation within the AI ecosystem. Furthermore,
the monopolisation of AI resources restricts the development of more sustainable and decentralised
approaches.
      </p>
      <p>
        While the challenges of centralisation, high retraining costs, and limited personalisation have long
constrained the evolution of large-scale AI systems, these can each be addressed in diferent ways
by continual learning. There are two fundamentally diferent types of forgetting in the context of
foundational models that necessitate continual learning as a solution: task-shift and time-shift forgetting
[
        <xref ref-type="bibr" rid="ref9">9</xref>
        ]. The first, task-shift forgetting , arises when a broadly pre-trained model is adapted to a new
downstream objective. Without careful safeguards, the updates that confer task skill can overwrite
previously acquired general knowledge. This can be efectively mitigated using techniques such as
continual pre-training (or domain adaptive pre-training) and continual fine-tuning. The second,
timeshift forgetting , occurs even when the task remains unchanged: as the external world evolves, the data
distribution shifts and a static model’s accuracy diminishes unless it is retrained. Additionally, the
scalability and modularity of model architectures need to be considered in order to enable models to
learn new tasks over time by dynamically composing task-specific modules to solve new tasks [
        <xref ref-type="bibr" rid="ref25">54</xref>
        ].
This notion of model compositionality is of the utmost importance to enable models to not only solve
novel tasks, but also to be dynamically orchestrated, facilitating interaction with one another in a
wider decentralised system of models. Whilst this ecosystem of interactive agents has already begun to
come to the fore [
        <xref ref-type="bibr" rid="ref13 ref26">55, 13</xref>
        ], all of these models are fundamentally static, requiring centralised retraining
over time, which is naturally prohibitive in encouraging more open, democratic and decentralised AI
systems.
      </p>
    </sec>
    <sec id="sec-4">
      <title>4. Three Key Research Directions for Continual Learning</title>
      <p>Here, we outline the three main research directions that are crucial for the future of Continual Learning,
namely Continual Pre-Training, Continual Fine-Tuning and Continual Compositionality &amp; Orchestration,
visualised in Figure 1. In the following sections, we will outline the requirements for each of these
separate components, challenges they face, open problems that are yet to be solved and how these
methods address the challenges within this context.</p>
      <sec id="sec-4-1">
        <title>4.1. Continual Pre-Training</title>
        <p>
          CPT refers to the process of incrementally updating the knowledge of FMs through exposure to new
data after their initial pre-training phase [
          <xref ref-type="bibr" rid="ref25">54</xref>
          ]. This iterative updating allows FMs to maintain their
foundational abilities established during the initial training while simultaneously adapting to assimilate
emerging information, thereby extending their operational lifespan and enhancing their adaptability to
the ever-changing landscape of data and knowledge [45].
        </p>
        <sec id="sec-4-1-1">
          <title>4.1.1. Motivation</title>
          <p>We now look to five main motivating factors to advance the field of CPT.</p>
          <p>
            Dynamic Knowledge Integration: CPT is primarily driven by the necessity to keep FMs relevant
and efective over time. Even large-scale foundation models can quickly become outdated as data
distributions shift and new knowledge emerges [
            <xref ref-type="bibr" rid="ref27">56</xref>
            ]. Static pre-training, performed on a fixed dataset,
inevitably leads to models losing touch with rapidly developing fields, where trends, terminologies and
societal norms continuously evolve, e.g. healthcare, law, technology. To address this challenge, CPT
performs a dynamic knowledge integration by continuously learning on new data streams, enabling
FMs to adapt and remain aligned with contemporary information [
            <xref ref-type="bibr" rid="ref28">57</xref>
            ]. Extensive studies have not only
demonstrated the necessity of CPT for improved downstream performance, but also shown that when
distributional shifts are gradual or somewhat correlated, CPT can efectively help models generalise
to previously unseen data [
            <xref ref-type="bibr" rid="ref9">9</xref>
            ]. In particular, CPT enables FMs to handle distributional shifts such as
temporal shifts (changes in data over time, leading to model drift), content shifts (changes in topic
or domain of the data) and language shifts (introduction of new languages or significant vocabulary
changes) [45].
          </p>
          <p>
            Methodological Evolution: CPT is also motivated by the ongoing improvements in model
architectures. Even when there is no new data or major distribution shift, updating foundation models can still
be valuable for adopting architectural advances that improve eficiency or performance. For instance,
transitioning from an encoder-decoder to a decoder-only architecture benefits from reusing existing
pre-trained models, which avoids the need to retrain from scratch and significantly reduces
computational cost. CPT enables this kind of update by initialising new models from previous checkpoints,
allowing them to retain useful learned knowledge while gradually adapting to architectural changes
[
            <xref ref-type="bibr" rid="ref29">58</xref>
            ].
          </p>
          <p>
            Resource Eficiency: Retraining FMs entirely from scratch on increasingly vast datasets becomes
computationally prohibitive over time. CPT significantly reduces these computational burdens by
incrementally updating models with new or domain-specific data, circumventing the need for repeated,
costly training cycles [
            <xref ref-type="bibr" rid="ref9">9</xref>
            ]. For instance, the LLaMA 4 Behemoth model [
            <xref ref-type="bibr" rid="ref30">59</xref>
            ], with its two trillion total
parameters, makes full retraining prohibitively expensive, whereas CPT allows for eficient incremental
adaptation of FMs.
          </p>
          <p>
            Mitigation of Catastrophic Forgetting: Static models, once trained, are frozen at their initial
knowledge cut-of, which creates a gap between initial training and real-world deployment needs. In
contrast, CPT fosters a continual evolution of models, bridging the gap between initial pre-training
and practical, lifelong learning scenarios. Notably, recent studies find that CPT can make models more
robust to catastrophic forgetting of earlier knowledge, especially when using self-supervised objectives,
highlighting CPT as a key enabler for foundation models to learn continuously like humans [
            <xref ref-type="bibr" rid="ref7">7</xref>
            ].
          </p>
          <p>
            Selective Forgetting: In addition to mitigating catastrophic forgetting, CPT has the potential to
support selective forgetting, where specific information embedded in a foundation model is intentionally
removed over time [
            <xref ref-type="bibr" rid="ref31">60</xref>
            ]. This capability is particularly relevant as large-scale models may inadvertently
memorise sensitive, outdated, or harmful content during pre-training [
            <xref ref-type="bibr" rid="ref32">61</xref>
            ]. Recent work has emphasised
the importance of enabling continual forgetting to remove such undesirable knowledge while preserving
overall model performance [
            <xref ref-type="bibr" rid="ref33">62</xref>
            ]. While earlier approaches explored this problem through fine-tuning,
recent eforts have extended it into the CPT phase. For example, Zhu et al. introduce a regularised CPT
method that enables the removal of backdoor behaviours in language models while maintaining their
functionality on clean data [
            <xref ref-type="bibr" rid="ref34">63</xref>
            ]. These developments highlight selective forgetting within CPT as a
promising direction for maintaining the safety, privacy, and reliability of foundation models over time.
          </p>
        </sec>
        <sec id="sec-4-1-2">
          <title>4.1.2. Challenges &amp; Open Problems</title>
          <p>
            CPT is still in the early stages of development, and bridging the gap between research and production
remains challenging: while CPT techniques show promise in controlled experiments, their long-term
stability and efectiveness over months of deployment in real-world settings remain under-explored [
            <xref ref-type="bibr" rid="ref9">9</xref>
            ].
This highlights several key challenges that must be addressed to make CPT viable in practice, including:
          </p>
          <p>
            Handling catastrophic forgetting: Catastrophic forgetting, the phenomenon where a continually
updated model loses previously acquired knowledge, remains a critical challenge in CPT [
            <xref ref-type="bibr" rid="ref35 ref36">64, 65</xref>
            ].
Although scaling up pre‑training tends to enhance knowledge transfer and resilience against forgetting
during downstream CL, excessively extensive pre‑training can significantly increase the risk of forgetting
[
            <xref ref-type="bibr" rid="ref37 ref38">66, 67</xref>
            ]. Recent studies indicate that self-supervised CL exhibits significantly reduced catastrophic
forgetting compared to supervised approaches [
            <xref ref-type="bibr" rid="ref39 ref7">68, 7</xref>
            ]. Indeed, self-supervised pre-training has the
advantage of reduced forgetting during upstream tasks, though efectively balancing upstream CL with
downstream continual adaptation remains an open research question [
            <xref ref-type="bibr" rid="ref40">69</xref>
            ]. Additionally, model scale
plays a pivotal role: larger models consistently demonstrate lower perplexity (an indicator of how
unfamiliar or novel a document is to a language model) and reduced forgetting, whereas smaller models,
despite achieving substantial learning gains, tend to exhibit the most pronounced forgetting efects [
            <xref ref-type="bibr" rid="ref41">70</xref>
            ].
          </p>
          <p>
            Balancing Eficiency vs. Model Drift: FMs often have hundreds of billions of parameters, so
retraining them on every new dataset is extremely computationally expensive [
            <xref ref-type="bibr" rid="ref25">54</xref>
            ]. Practical CPT must
therefore be computationally eficient, for instance by updating only a subset of parameters or using
limited data, but this can exacerbate the stability–plasticity dilemma. Insuficient or biased updates
may lead to model drift, where performance on original domains degrades or the model’s behaviour
shifts unpredictably. Empirically, a “stability gap” has been observed: when an LLMs is first continually
pre-trained on a new domain, its performance drops initially (due to distribution shift) before recovering
[
            <xref ref-type="bibr" rid="ref42">71</xref>
            ]. Balancing eficient adaptation with stability (avoiding regressions on prior knowledge) is an open
problem.
          </p>
          <p>
            Avoiding reinforcement of biases in pre-training: Continuously ingesting new data can also
reinforce biases or fairness issues if not carefully controlled. If the incoming data is skewed or uncurated,
the model might amplify these biases over time, undermining responsible use. For example, biomedical
FMs trained on federated data must address fairness across diverse populations while preserving privacy
[
            <xref ref-type="bibr" rid="ref43">72</xref>
            ]. Ensuring that continual updates do not degrade the model’s ethical alignment (e.g. with respect
to bias and fairness) is crucial [
            <xref ref-type="bibr" rid="ref25">54</xref>
            ]. Methods to detect and mitigate bias drift during CPT (and to curate
update data) are largely lacking and represent an important research frontier.
          </p>
        </sec>
        <sec id="sec-4-1-3">
          <title>4.1.3. Potential Solutions &amp; Future Research Directions</title>
          <p>To address the challenges of CPT and unlock its full potential, several promising solutions and future
research directions have been proposed, including:</p>
          <p>
            Incremental pre-training strategies: Recent works propose reusing or initialising from previous
model weights to maintain continuity, as in recyclable tuning methods that carry over knowledge from
an old model to a new one [45]. Recent work has demonstrated the benefits of structured or multi-stage
CPT. For instance, in [
            <xref ref-type="bibr" rid="ref44">73</xref>
            ], a two-step CPT was shown to enable a mixed-language neural machine
translation system (first adapting to a language domain, then to a specific translation task) efectively.
In [
            <xref ref-type="bibr" rid="ref45">74</xref>
            ], Dalla Noce et al. introduce a sequential CPT framework for neural machine translation, where
a model is progressively exposed to new language pairs or domains in multiple stages. Their study
ifnds that incrementally adding new languages during the pre-training phase does not substantially
degrade the model’s performance on previously seen language pairs during fine-tuning. Furthermore,
incorporating CL strategies such as data rehearsal can further reduce performance loss on earlier
language pairs compared to purely incremental pre-training but comes with increased computational
cost during the training phase. This highlights a practical trade-of between training eficiency and
performance robustness: reasonable downstream performance can be achieved through incremental
pre-training, but further performance improvements can be attained when accepting the additional
computational cost associated with CL strategies.
          </p>
          <p>
            Selective memory and rehearsal methods: To combat forgetting, memory replay methods have
shown promise in the context of foundation models. Rather than relying only on the latest data, the
model can intermittently rehearse on representative samples of past data (or tasks). In practice, storing
raw past data for a foundation model may be impractical or raise privacy concerns such that recent
work leverages latent replay, where the model saves a cache of compact feature representations or
embeddings of past examples instead of the raw inputs [
            <xref ref-type="bibr" rid="ref25">54</xref>
            ]. During CPT, these stored latent vectors can
be replayed through the model to reinforce previously learned concepts. This memory-eficient replay
has been shown to significantly mitigate forgetting in vision models and is especially valuable when
sharing raw data is prohibited (e.g. user data privacy). Besides replay, selective sampling strategies
can be used rather than naively mixing new data; the training scheduler might interleave the most
informative or relevant examples carefully chosen from older tasks or emphasise dificult examples that
the model is starting to forget. There is evidence that the order and composition of training data in CPT
can greatly afect retention [
            <xref ref-type="bibr" rid="ref27">56</xref>
            ]. For example, Xie et al. use perplexity and embedding similarity metrics
to select a fraction of a domain corpus that achieves comparable adaptation with far less training cost
[
            <xref ref-type="bibr" rid="ref46">75</xref>
            ]. Such sampling not only improves eficiency but can also prevent the model from drifting too far
by ensuring the new training distribution is aligned with the model’s original knowledge. Additionally,
some approaches intermix new data with a small portion of the original pre-training data (or a similar
distribution) during updates, explicitly to reduce distribution shift [
            <xref ref-type="bibr" rid="ref42">71</xref>
            ]. This kind of rehearsal or data
mixing has been shown to narrow the stability gap and avoid performance deterioration on earlier tasks.
Going forward, developing principled sampling and replay policies (potentially guided by uncertainty,
importance weighting, or task identities) is a key research direction to make CPT robust and scalable.
          </p>
          <p>
            Self-supervised continual adaptation techniques: CPT largely relies on self-supervised learning
objectives such as predicting masked tokens, next sentence prediction, and image-text contrastive
learning, because these allow the use of unlabelled streaming data. An intriguing finding from recent
research is that self-supervised objectives can themselves be leveraged to improve CL. In [
            <xref ref-type="bibr" rid="ref7">7</xref>
            ], Cossu et
al. provide strong empirical evidence that continuing pre-training models in a self-supervised manner
yields better knowledge retention than supervised training in the continual setting. Intuitively,
selfsupervised learning updates may be softer or more difuse in the parameter space (since they capture
broad patterns in data) compared to task-specific fine-tuning which might overwrite more specialised
parts of the model. In [
            <xref ref-type="bibr" rid="ref47">76</xref>
            ], Ostapenko et al. also observed that models pre-trained with broader or
more diverse self-supervised signals tend to forget less and transfer better in downstream sequential
tasks. This suggests that self-supervised CPT is a promising avenue: as new unlabelled data comes
in, one can design auxiliary objectives that encourage the model to integrate new information while
maintaining consistency with prior representations. Techniques like contrastive learning on a replay
bufer, or predictive modelling that ties new concepts to old ones, fall in this category. Moreover,
self-supervision can be combined with light supervision or prompts in an autonomous CL setup (where
a model might generate pseudo-labels or questions on new data and learn from them). Overall,
selfsupervised learning-based CPT not only provides a means to utilise vast unlabelled streams, but also
appears to inherently mitigate forgetting, making it a key research direction for lifelong FMs.
          </p>
        </sec>
      </sec>
      <sec id="sec-4-2">
        <title>4.2. Continual Fine-tuning</title>
        <p>Continual fine-tuning is the practice of applying a stream of lightweight, task‑specific updates to a
model after deployment, allowing it to evolve alongside newly arriving data rather than remaining
ifxed after a single adaptation.</p>
        <sec id="sec-4-2-1">
          <title>4.2.1. Motivation</title>
          <p>
            Fine-tuning is attractive because it it far cheaper than full retraining, requires only task-specific data,
and can be executed on modest hardware [
            <xref ref-type="bibr" rid="ref48 ref49">77, 78</xref>
            ]. Yet, once the weights are written to disk, the model
is frozen again. In realistic deployments, data arrives as a stream, such as customer queries, sensor
logs, freshly published documents — therefore the ability to fine-tune continually is crucial [
            <xref ref-type="bibr" rid="ref50 ref51">79, 80</xref>
            ].
CFT turns a one-shot adaptation step into a standing capability that (i) personalises responses for
each user or organisation [
            <xref ref-type="bibr" rid="ref52">81</xref>
            ], (ii) keeps proprietary data on-premise for privacy compliance [
            <xref ref-type="bibr" rid="ref53">82</xref>
            ], (iii)
reacts quickly to domain drift without the latency of retrieval augmented generation (RAG) pipelines or
very long context windows [
            <xref ref-type="bibr" rid="ref16">16</xref>
            ], (iv) does all of this with a fraction of the compute budget needed for
repeated full-scale updates [
            <xref ref-type="bibr" rid="ref54 ref55">83, 84</xref>
            ]. The need for CFT, the process of incrementally fine-tuning a model
to help it adapt to downstream tasks that involve shifting data distributions and temporal changes [
            <xref ref-type="bibr" rid="ref50">79</xref>
            ],
cannot be overstated.
          </p>
          <p>Although FMs have demonstrated impressive versatility across diferent tasks, with the ability to
generalise efectively to various domains, their static nature limits the capacity to incorporate new
knowledge, adapt to specialised fields, and personalise outputs over time. CFT presents an important
opportunity to make foundation models more flexible, eficient and responsive to real-world changes,
making them more useful in more dynamic environments. While continual pre-training focuses on
updating a model’s general representations using broad, often unlabelled data, continual fine-tuning
instead aims to incrementally adapt the model to specific downstream tasks using labelled or structured
data, with an emphasis on retaining prior knowledge while learning new information.</p>
        </sec>
        <sec id="sec-4-2-2">
          <title>4.2.2. Challenges &amp; Open Problems</title>
          <p>CFT in the context of foundation models like LLMs comes with several challenges such as:</p>
          <p>
            Balancing Specificity vs. Generalisation : CFT must maintain a delicate equilibrium between
tailoring a model to a specific downstream task and preserving its broad, generalisable knowledge. When
a model undergoes CFT, its internal representation becomes optimised to capture patterns necessary for
solving a specific downstream task. While this adaptation enhances the performance on domain specific
tasks, it risks eroding the broad, general-purpose representations learned during pre-training. This
comes back to the stability-plasticity dilemma where models must remain plastic enough to integrate
task-specific knowledge while being stable enough to retain the broad representations acquired from
prior experiences [
            <xref ref-type="bibr" rid="ref56">85</xref>
            ].
          </p>
          <p>
            Eficient Adaptation Without Catastrophic Forgetting : In a similar vein to CPT, catastrophic
forgetting is also experienced by CFT methods, however within this context eficient adaptation also
needs to be considered. This concept refers to the process of updating a pre-trained foundation model
to perform well on new tasks, domains, or data distributions while minimising computational resources,
data requirements, and training time. In the context of LLMs and other foundation models, eficiency
has become increasingly critical as these models grow to billions of parameters. Eficient finetuning
techniques like LoRA [
            <xref ref-type="bibr" rid="ref49">78</xref>
            ] allow large pre-trained models to be adapted to downstream tasks by updating
only a fraction of the model’s original parameters, but these techniques are still prone to catastrophic
forgetting.
          </p>
          <p>Data eficiency and privacy concerns in continual fine-tuning : CFT deals with the dual
challenges of data scarcity and privacy concerns, especially in specialised domains to efectively adapt
models to new tasks. As foundation models are adapted to increasingly specialised domains, high-quality,
domain-specific data becomes progressively scarcer [ 86].</p>
        </sec>
        <sec id="sec-4-2-3">
          <title>4.2.3. Potential Solutions &amp; Future Research Directions</title>
          <p>Despite these limitations, numerous methods have been developed to tackle these challenges.</p>
          <p>
            Parameter Eficient Fine-Tuning A key methodological tool in the context of CFT is represented
by Parameter Eficient Fine-Tuning (PEFT) methods. These techniques aim to achieve performance
comparable to or even surpass full model fine-tuning while updating only a small number of trainable
parameters, either by selectively updating a subset of the model’s parameters [
            <xref ref-type="bibr" rid="ref49">78</xref>
            ] or introducing
new task-specific parameters [
            <xref ref-type="bibr" rid="ref48">77</xref>
            ]. PEFT methods are particularly advantageous in continual learning
scenarios, where models must adapt to a sequence of tasks without forgetting previously learned
information.
          </p>
          <p>By updating only a limited number of parameters, PEFT approaches reduce computational overhead
and, when applied properly, can help mitigate the risk of catastrophic forgetting. Among these PEFTs,
Prompt Adapters and LoRA are the most widely used. LoRA works by introducing low-rank updates to
the pre-trained model weights, expressed as:
 = 
0 + 
(1)
where the pre-trained model  0 is kept frozen, while the low-rank matrices  and  are updated.</p>
          <p>Prompt-based techniques like L2P and CoDA Prompt [87, 88] incrementally learn from novel data by
designing task-specific prompts that guide the model’s attention toward relevant information for each
new task, facilitating seamless integration of new knowledge without overwriting existing capabilities.</p>
          <p>
            Similarly, LoRA-based CL approaches, such as C-LoRA and DualLoRA [
            <xref ref-type="bibr" rid="ref52">81, 89</xref>
            ], enhance LoRA’s
applicability in CL by introducing mechanisms like learnable routing matrices and orthogonal subspaces
to manage parameter updates across tasks, thereby reducing computational overhead and mitigating
catastrophic forgetting.
          </p>
          <p>Adapter techniques like Continuous Adapter (C-ADA) and Adapter-based Continual Learning (ACL)
[90, 91] instead ofer more eficient solutions for CL. C-ADA introduces a Continual Adapter Layer that
extends weights for new tasks while freezing old ones, preserving prior knowledge. It also employs
a Scaling &amp; Shifting module to align feature spaces between pre-training and downstream datasets.
Similarly, ACL utilises lightweight, task-specific adapters within a fixed pretrained feature extractor and
incorporates a task-specific head that groups previously learned classes into an ”out-of-distribution”
category, facilitating efective feature discrimination.</p>
          <p>Model Merging: A particularly valuable approach when facing dynamic environments is given
by Model Merging. The key point in this class of methods is to combine multiple specialised models
learned over time, to create systems that preserve knowledge while adapting to new tasks. The central
challenge in model merging is parameter interference, where integrating diferent models leads to
performance degradation. Recent research has developed several innovative solutions to this problem.
TIES-MERGING [92] addresses interference by strategically resetting minimally changed parameters
and resolving sign conflicts between models. In contrast, DARE [ 93] employs a diferent strategy by
randomly dropping redundant delta parameters and rescaling the remaining ones, efectively sparsifying
merged models without significant performance loss.</p>
          <p>While early model merging techniques focused on the static combination of pre-existing expert models,
more recent approaches support dynamic integration as new tasks emerge over time. MagMax [94]
introduces sequential fine-tuning with maximum magnitude weight selection to efectively incorporate
new information while preserving earlier learning. Representation Surgery [95] tackles representation
bias by inserting lightweight task-specific modules that realign internal representations between
merged models. Adaptive LoRA Merging [96] moves beyond fixed-weight combinations by dynamically
computing merging coeficients that balance contributions from new and old domains.</p>
          <p>
            Recent trends in CFT have shifted towards the adaptive integration of lightweight modules, like
adapters [
            <xref ref-type="bibr" rid="ref48">77</xref>
            ] and LoRA [
            <xref ref-type="bibr" rid="ref49">78</xref>
            ], in dynamic environments. This shift enables seamless integration of
new tasks without extensive retraining of large models. By merging these modular components on
demand, systems can eficiently handle real-world challenges while remaining practical for large-scale
deployment.
          </p>
          <p>
            Meta Learning for Continual Adaptation: An alternative perspective on the challenge of CFT
is ofered by meta learning approaches for continual adaptation. In fact, these methods integrate
adaptability into the core learning objective, enabling models to rapidly adjust to new tasks with
minimal data and computation. Traditional meta-learning approaches like Model-Agnostic
MetaLearning (MAML) [97] operate by finding parameter initialisations that enable rapid adaptation across
a distribution of tasks. When applied to CL scenarios, these methods can be extended to discover
parameter configurations that not only adapt quickly but also resist catastrophic forgetting. For instance,
ANML [
            <xref ref-type="bibr" rid="ref51">80</xref>
            ] uses a neuromodulatory network that enables the model to focus on relevant tasks while
minimising interference from previously learned tasks.
          </p>
          <p>Recent works have combined meta-learning with parameter-eficient fine-tuning techniques to
enhance CL. AutoLoRA [98] introduces a meta-learning framework that automatically identifies the
optimal rank for each LoRA layer, improving adaptation eficiency to new tasks while maintaining
performance on previous ones. Similarly, Meta-LoRA [99] presents a memory-eficient method for
automatic sample re-weighting during fine-tuning, facilitating eficient continual adaptation across
various domains. These approaches exemplify the potential of meta-learning to enhance the adaptability
and eficiency of foundation models in dynamic environments.</p>
          <p>
            Federated Learning (FL) and Decentralised Fine-Tuning Strategies: Moving towards the
direction of a distributed and decentralised AI development, FL is essential for efectively adapting
large FMs across organisations, while preserving data privay and optimising computational resources.
When applied to FMs, however, FL faces unique challenges. The vast number of parameters in modern
FMs makes server-client communication prohibitively expensive. Diferent clients naturally generate
data with varying distributions, creating potential conflicts in optimisation objectives. Frameworks like
FATE-LLM [
            <xref ref-type="bibr" rid="ref53">82</xref>
            ] enable collaborative training of LLMs by employing parameter-eficient fine-tuning
methods and incorporating privacy-preserving mechanisms. FibecFed [
            <xref ref-type="bibr" rid="ref54">83</xref>
            ] enhances this approach
by utilising Fisher information for adaptive data sampling and dynamically selecting layers for global
aggregation, thereby improving both performance and fine-tuning speed. Additionally, FedRewind
[100] introduces a decentralised model exchange strategy inspired by continual learning principles,
addressing data distribution shifts and enhancing generalisation performance in federated settings.
          </p>
        </sec>
      </sec>
      <sec id="sec-4-3">
        <title>4.3. Continual Compositionality &amp; Orchestration</title>
        <p>Continual Compositionality &amp; Orchestration refers to the dynamic integration of multiple AI agents
over time, to solve higher-level tasks. It is the key component towards a distributed and decentralised
AI framework.</p>
        <sec id="sec-4-3-1">
          <title>4.3.1. Motivation</title>
          <p>Large models solved most of the tasks addressed by AI methods for decades. In fact, using a
Transformerbased architecture, pre-trained on some large dataset, we now know how to solve almost every task,
provided enough data and computational power. Broadly speaking, modern FMs have achieved
superhuman performance on most of the traditional machine learning benchmarks, making them obsolete
and less relevant for current AI research.</p>
          <p>For this reason, we are now shifting towards higher level tasks, which require a higher level of
intelligence, that current state-of-the-art models do not exhibit. This trend is demonstrated by the
emergence of several more complex benchmarks, that could drive the research beyond current LLMs.
One such benchmark is ARC-AGI [101], which consists of simple grid transformations. Despite being
simple for a human solver, it poses great challenges, requiring strong abstraction skills and inductive
reasoning. Another example is BIG-bench [102], a collection of more than 200 tasks, designed to test the
limits of current large models. The benchmark covers a broad set of tasks, including linguistics,
mathematics, common-sense reasoning, social bias detection and more. In both cases, human performance
significantly surpasses the current best models, highlighting the need for alternative solutions.</p>
          <p>Furthermore, latest large models, e.g. GPT 4.5, demonstrate that we are rapidly moving towards
a diminishing returns regime, meaning that just increasing the model dimensions and the number
of GPUs employed is no longer enough to obtain noticeable improvements [103]. We believe that a
paradigmatic change is needed in the AI community in order to push research forward and to obtain
more intelligent behaviours.</p>
          <p>Our proposal is to address some of the shortcomings that current solutions exhibit, particularly
regarding scalability and sustainability matters, with Continual Compositionality and Orchestration
approaches. Nowadays, the de facto standard is to have single, monolithic models, trained once and
deployed without any guarantees on their utility over time. CCO instead represents a framework built
on the communication between multiple AI models, which share their knowledge and skills in terms of
model parameters, deep representations or final predictions.</p>
          <p>Within this paradigm, the orchestration among the agents becomes crucial: depending on the task,
diferent modules are selected to be composed in various fashions. In other words, rather than adjusting
a single network to a dynamic scenario, CCO employs a modular approach, where diferent module
compositions can be used to adapt to non-stationary environments over time. Also, such a framework
does not impose constraints on the scalability of the system, i.e. the number of modules involved, and it
is more sustainable by design, since the modules are trained once and then re-used over time in multiple
ways.</p>
        </sec>
        <sec id="sec-4-3-2">
          <title>4.3.2. Challenges &amp; Open Problems</title>
          <p>With the advancements in capabilities of LLMs, there has been a growing research focus on building
LLM-based agent architectures, in which multiple models are composed and coordinated to solve
complex tasks [104, 105]. We can place agents on a spectrum based on their level of autonomy in order
to diferentiate their architectures. On one end, fully autonomous systems, in which agents interact
with significant freedom; on the other, predictable and structured workflows, in which agents follow
predefined steps and communication patterns [ 106]. More structured and predetermined workflows
might be preferable for domains that require more precision and accountability, such as mathematical
reasoning, scientific research, law, medicine, and software development.</p>
          <p>
            Task Decomposition and Specialisation: An efective strategy to enable LLMs to solve complex
problems is to break them down into simpler, more manageable sub-tasks [
            <xref ref-type="bibr" rid="ref25">107, 108, 54</xref>
            ]. However,
fully automating the planning and decomposition of tasks into sub-tasks with LLMs is an area of open
research. Some studies propose decomposing a problem with a single LLM request that generates a series
of sub-steps [109, 110, 111]. Other studies propose more advanced search-based approaches, which
iterate and further decompose each sub-task into smaller steps when necessary; the final execution
plan can then be organised into a tree-like structure [112]. One major challenge of this area of research
is generating plans for domain-specific problems; the use of external planners is one of the solutions
that have been proposed to address this issue [105]. Additionally, the planning abilities of LLMs might
still be limited by their lack of human-level comprehension of world dynamics and the ability to apply
causal reasoning to them [106].
          </p>
          <p>Within this context, Mixture-of-Experts (MoE) models have emerged as a prominent line of research,
ofering a natural implementation of the divide and conquer paradigm. MoE architectures aim to
scale model capacity eficiently by activating only a subset of experts per input, leading to improved
performance [113, 114]. However, a core challenge lies in achieving efective expert specialisation
— ensuring that each expert acquires unique and distinct skills, with little overlap with the others.
Preliminary works suggests that expert models specialise on superficial patterns, such as token IDs,
rather than extracting high-level semantic information [115]. Although recent eforts have proposed
solutions towards more meaningful expert specialisation [116], we still lack a clear understanding of
these mechanisms, especially when considering distributed and decentralised AI frameworks. Further
research is needed to ensure that MoE models can robustly and adaptively decompose complex tasks in
dynamic, multi-agent environments.</p>
          <p>Role-based Collaboration and Interactions: In a compositional framework, interactions among
agents represents a key ingredient. One of the most common strategies to compose multiple agents to
work together in solving a task is the so-called role-based collaboration. LLM-based agents assume
clearly defined, specialised roles (such as domain experts, assistants, etc.) in order to solve a higher level
goal, with each of them being assigned individual sub-tasks by other agents. Optimal role assignments
and agent adaptability to dynamic tasks requirements are still areas of open research [104]. One
challenge is that, while LLMs are able to simulate many common roles, there are still many roles that
they might not be able to capture accurately, such as uncommon roles rarely seen in the training
corpus, or roles corresponding to human characters with particular cognitive-psychological traits
[117, 118, 105].</p>
          <p>Additionally, agent interaction play an essential role for multi-round tasks, where multiple iterative
feedbacks loops — both from the environment and from other agents — are required to achieve the
objective. Such tasks demand dynamic coordination, contextual adaptation, and the ability to reason
over partial progress. Recent studies have begun to explore this promising topic, introducing novel
solutions for LLM collaboration [119, 120]. This underscores the relevance of multi-agent interactions
as a key challenge for CCO.</p>
          <p>Propagation of errors: Lastly, the propagation of errors is an additional open problem in ensuring
robustness in model integration. Erroneous outputs, hallucinations and biases from one agent can have
cascading efects, getting amplified and spread through model interactions and impacting the whole
system [104].</p>
        </sec>
        <sec id="sec-4-3-3">
          <title>4.3.3. Potential Solutions &amp; Future Research Directions</title>
          <p>The concept of multiple models collaborating within a shared environment is well established in the
AI field, and is rooted in the foundational definition of multi-agent systems (MAS). Such systems
consist of multiple autonomous agents, each with its own goals and motivations, that are capable of
interacting with one another. For this reason, a central focus of this paradigm is on cooperation and
coordination among agents.</p>
          <p>The CCO framework can be viewed as a concrete instantiation of MAS, where models such as LLMs
must be orchestrated to achieve a common objective. A key research direction in this context is the
dynamic selection and composition of the most appropriate agents for a given task. Indeed, in the CCO
framework the goal is to enable automatic models composition, that can evolve dynamically over time
in response to variations in the environment or in the task given by the user. This marks a significant
advancement over existing compositionality frameworks, e.g. LangGraph1, AutoGen [121], in which
the orchestration is largely static and predefined by the programmer, thereby limiting both flexibility
and the capacity to generalise across tasks and environments.</p>
          <p>
            Another component enabling continual learning capabilities in the CCO framework could be the use
of experience accumulation modules, in the form of memory modules and skill libraries, as proposed in
works like GITM, Voyager, AppAgent and MemPrompt [122, 123, 124, 125]. These approaches allow
models to dynamically acquire new knowledge and skills, as a result of interactions with other agents,
humans and the environment [105, 108, 126]. Such knowledge and skills can be stored in natural
language or code form, and later retrieved and added to the model input context as needed. These
mechanisms rely on test-time inference and incorporate the new knowledge and skills in the input
context window of the model. One limitation might be that, depending on the LLM used, the context
window capacity might limit the amount of task information that can be incorporated; however, research
advancements in this area are enabling ultra-long context windows of 1M tokens or more [
            <xref ref-type="bibr" rid="ref16">16</xref>
            ], albeit at
the expense of added compute.
          </p>
          <p>An additional crucial aspect lies in the communication between agents. In the case of LLM agents,
communication can occur through natural language, which has the added benefit of being easily
interpretable by human users — a property that enhances transparency and human-in-the-loop control
[127]. However, the CCO framework is designed to be model-agnostic and general-purpose, extending
beyond language models to integrate a diverse set of AI components — such as computer vision models,
time series processors, rule-based systems, symbolic modules or even hard-coded functions.
To support such heterogeneity, the system requires a robust communication protocol, that accommodates
decentralisation, asynchrony and diferent data formats, while enabling eficient knowledge exchange.</p>
          <p>Furthermore, an important open question in the design of the CCO protocol is in what type of
knowledge should be shared among agents, to maximise collaboration without unnecessary overheads.
Depending on the use case, this could include (i) model parameters, either in entirety or specific
subnetworks / modules; (ii) the model internal representation, e.g. latent vectors or output logits; (iii)
training data, as raw samples or abstracted via data generators.</p>
        </sec>
      </sec>
    </sec>
    <sec id="sec-5">
      <title>5. The Future of Continual Learning: From Niche Research to AI’s</title>
    </sec>
    <sec id="sec-6">
      <title>Next Paradigm</title>
      <p>
        Over the past decade, Continual Learning (CL) has established itself as a prominent research area
exploring a variety of domains, problem settings and applications [25]. In Computer Vision, significant
efort has been committed to class incremental and domain incremental scenarios, where models must
progressively recognise new categories without forgetting previously learned ones, even as the input
domains evolve [128]. In Reinforcement Learning, CL has focused on the ability of agents to adapt
dynamically to evolving environments while retaining past knowledge and abilities, particularly in task
incremental and multi-task settings [129]. More recently, CL research has extended its scope to include
LLMs and Foundational Models, where the challenge lies in enabling models to continuously acquire
new linguistic capabilities or domain knowledge without catastrophic forgetting [
        <xref ref-type="bibr" rid="ref25 ref9">54, 9</xref>
        ]. Another
critical aspect is memory management in lifelong learning AI systems. Several studies examine the
inherent trade-of between limited computational and storage resources and the ever-growing volume
of data that CL models are expected to handle. Researchers have proposed a wide range of methods
to strike a balance between learning eficiency and memory constraints such as dynamic memory
bufers, experience replay mechanisms, architectural approaches, and regularisation techniques [ 25, 26].
Leveraging this attention from the community, CL has become a well-established and recognised field,
providing both theoretical foundations and practical methodologies for building adaptive, robust, and
memory-eficient AI systems.
      </p>
      <p>Given the increasingly consolidated position of CL within the research community, we believe the
time is right for the field to take a decisive step forward. Rather than representing a separate area of
study, CL should become a critical and fundamental component in the prototyping and evolution of
modern AI systems. In particular, the rapid rise of foundational models has captured the attention of
both academia and industry, asserting itself as one of the most prominent and transformative trends
in contemporary AI research. These models showcase broad generalisation capabilities across tasks
and modalities; however, they still exhibit a critical limitation: their knowledge is inherently static and
ifxed at training time. This immutability poses a major challenge in dynamic real-world environments,
where new data and information continuously emerge.</p>
      <p>To address this gap, foundational models must evolve towards true continuous adaptation,
progressively updating, refining, and extending their knowledge over time. Continual learning principles can
provide a concrete and resourceful solution in this context. As previously discussed, Continual
Pretraining and Continual Fine-tuning represent emerging research directions that aim to integrate the
principles of CL with large-scale models, enabling them to remain updated, accurate, and contextually
relevant, thereby mitigating outdated or incorrect outputs [45]. However, CPT and CFT inherently
require relatively low-frequency adaptation cycles and depend on substantial computational resources.
Thus, while beneficial, these approaches alone might not address the dynamic adaptability required by
real-world applications fully.</p>
      <p>
        Real-world change, in contrast, is often expressed at the level of orchestration: new tools appear [
        <xref ref-type="bibr" rid="ref26">55</xref>
        ],
regulations shift, a CoT must be revised, or a group of agents must re-organise to solve an emergent
sub-problem [
        <xref ref-type="bibr" rid="ref13">13</xref>
        ]. This layer is inherently high-frequency and pervasive, with potential updates required
minutes or even seconds after new data arrives, making repeated ofline training cycles impractical
[
        <xref ref-type="bibr" rid="ref15">15</xref>
        ]. Here Continual Compositionality and Orchestration is not merely advantageous - it is
indispensable. CCO treats an AI system as a living assembly of modules composed of prompt routers,
domain experts, external tools, episodic memories — all of which can be composed and adapted on
the fly. Continual learning supplies the two capabilities such a system requires: rapid adaptation to
integrate the next tool or component and memory consolidation to stabilise useful compositions so that
they can be re-used rather than rediscovered.
      </p>
      <p>
        Foundational models are generally efective across broad tasks; however, when maximising
performance in specialised areas, such as mathematics or physics, monolithic models may underperform
compared to models specifically distilled or trained for those individual tasks [ 130, 131]. We believe
that creating and deploying CL models which can continually evolve and combine knowledge from
diferent sources represents a promising and sustainable architectural solution for AI systems. Moreover,
developing models that are a mixture of many components [
        <xref ref-type="bibr" rid="ref25">54, 132</xref>
        ] can allow for the distribution of
computation and decentralisation of AI systems. Diferent institutions can collaborate and contribute
to create the ad-hoc models that synergise to achieve the final and complete AI system.
      </p>
      <p>
        Furthermore, aligning with recent advances, foundational models can also be improved through
human feedback within a Reinforcement Learning from Human Feedback (RLHF) framework, where
humans actively guide model evolution, shaping future AI outputs and capabilities in turn [
        <xref ref-type="bibr" rid="ref24">53</xref>
        ]. This
human-AI feedback loop can help to ensure that AI development is in line with human preferences
and can also be applied within the context of multi-agent systems. Human-in-the-loop approaches in
agentic LLM systems can be used to provide guidance, supervision and feedback to individual agents,
facilitating alignment with human preferences [
        <xref ref-type="bibr" rid="ref14">108, 133, 134, 14</xref>
        ].
      </p>
      <p>In summary, Continual Learning, specifically continual compositionality and orchestration, represents
not only a promising research direction, but the cornerstone of AI’s next paradigm shift. By transitioning
from incremental improvements within individual models to dynamically composable and collaborative
AI ecosystems, CL can drive a new generation of adaptive, scalable and human-aligned AI systems.</p>
    </sec>
    <sec id="sec-7">
      <title>6. Conclusion</title>
      <p>The remarkable capabilities of large foundational models highlight their potential in solving complex,
diverse tasks across multiple domains. However, despite their robust generalisation abilities, these
models are inherently static and struggle to adapt continually to evolving real-world data and tasks. To
overcome these limitations, continual learning emerges as an indispensable tool, ofering a multitude of
methodologies to enhance adaptability, eficiency and sustainability within foundational models.</p>
      <p>In this paper, we have highlighted three pivotal areas of continual learning critical to the evolution
of FMs: continual pre-training, continual fine-tuning, and continual compositionality and orchestration.
CPT equips very large, organisation-scale models with the mechanisms to incrementally incorporate
new knowledge, capabilities or methodologies, maintaining their relevance and mitigating catastrophic
forgetting through adaptive, resource-eficient updates. As such, it is mainly within the remit of
industrial laboratories and cloud providers who possess the necessary data and compute. CFT remains
valuable, although comparatively secondary, to enable precise adaptation to specialised tasks and
domains, efectively balancing specific task performance with the retention of generalisable knowledge.
Techniques such as PEFT, meta-learning and model merging were identified as promising approaches
to achieving efective adaptation while managing computational resources and limiting data drift.</p>
      <p>CCO, by contrast, is where academic research can and should place its primary emphasis. Moving
from monolithic models to a decentralised ecosystems composed of specialised, modular agents
facilitates adaptability, enhances scalability and reduces centralisation risks by enabling modular model
replacement, upgrade and collaborative interaction. By studying and advancing CCO, the research
community can catalyse an open, decentralised, and circular economy of AI components. Such a
decentralised ecosystem not only encourages innovation and democratises access, but also mitigates
the computational and environmental costs associated with continually retraining large, static models.</p>
      <p>Ultimately, continual learning positions itself not merely as an optional enhancement but as a
foundational requirement for future AI systems. As AI evolves from static to dynamic, from centralised
to decentralised, and from monolithic to modular, the integration of continual learning methodologies
will be crucial. Embracing continual learning will therefore be instrumental in building resilient, flexible
and context-aware AI systems, capable of sustainably adapting to the ever-changing landscape of
real-world challenges.</p>
    </sec>
    <sec id="sec-8">
      <title>Acknowledgments</title>
      <p>Research partly funded by PNRR - M4C2 - Investimento 1.3, Partenariato Esteso PE00000013 - ”FAIR
- Future Artificial Intelligence Research” - Spoke 1 ”Human-centered AI”, funded by the European
Commission under the NextGeneration EU programme.</p>
    </sec>
    <sec id="sec-9">
      <title>Declaration on Generative AI</title>
      <p>During the preparation of this work, the author(s) used OpenAI ChatGPT-4o in order to: Grammar and
spelling check, Paraphrase and reword. After using these tool(s)/service(s), the author(s) reviewed and
edited the content as needed and take(s) full responsibility for the publication’s content.
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