Training Custom Large Language Models

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In the dynamic world of artificial intelligence, Large Language Models (LLMs) have emerged as remarkable and flexible tools, transforming how machines understand, produce, and manipulate human language. These models, rooted in deep learning and natural language processing, have showcased extraordinary capabilities in various applications, spanning from machine translation and sentiment analysis to question-answering systems and chatbots.

LLMs represent a class of AI designed by training on extensive datasets of text and code. Their application possibilities are diverse and include the following:

  • Chatbots and virtual assistants
  • Language translation
  • Content creation
  • Question answering
  • Summarization
  • Code generation

As LLMs evolve, their power and adaptability continue to grow, leading to widespread adoption across industries. Businesses employ them to enhance customer service, researchers benefit from generating novel insights, and educators create personalized learning experiences.

Training Custom Large Language Models

Source: Photo by Pavel Danilyuk

Armed with a vast number of parameters, these models adeptly capture intricate language patterns, contextual relationships, and semantic nuances. Some of the most prominent LLMs today, such as OpenAI’s GPT, Google’s BERT, and Pathways Language Model 2 (PaLM 2), are built on the transformer model, reflecting their widespread adoption and recognition in natural language processing. An essential advantage of LLMs is their customizability for specific tasks and domains; the model’s performance can be optimized and refined.

However, training LLMs from scratch is a daunting challenge for individuals due to several compelling reasons:

  • Enormous Computational Resources: The sheer size of LLMs, with millions or billions of parameters, demands substantial computational power, often exceeding the capabilities of individual machines. Specialized hardware or high-performance GPUs are required for efficient training.
  • Extensive Training Time: Pre-training LLMs on massive datasets can take weeks or months. Training from scratch would only extend this timeframe, making it impractical for individuals given limited computational resources and the opportunity cost of time.
  • Data Requirements: Successful pre-training relies on vast and diverse datasets, typically collected from the internet or extensive corpora. The effort involved in acquiring, cleaning, and preprocessing such data is significant and beyond the capacity of individuals.
  • Cost and Infrastructure: The cost of training LLMs from scratch can be prohibitive, encompassing expenses for hardware, cloud computing, and potentially hiring specialized experts.
  • Access to Datasets: Pre-training LLMs often necessitates using proprietary or licensed datasets, limiting access to research institutions and companies and making it challenging for individuals to obtain these resources.
  • Maintaining Models: After training, LLMs require ongoing monitoring, maintenance, and updates to remain relevant and efficient. This ongoing effort demands resources and expertise that may exceed an individual’s capabilities.
  • Expertise and Know-How: Successfully training LLMs requires profound knowledge of natural language processing, deep learning, and the intricacies of underlying model architectures. Expertise covering optimizing LLMs during training involves addressing issues like overfitting, underfitting, and fine-tuning hyperparameters. This process requires extensive experimentation and expertise to achieve optimal performance.

Given these complexities, the practical approach for most individuals and organizations is to leverage pre-trained LLMs, building upon existing models to create custom solutions tailored to their specific tasks and domains and save time and computational resources.

Custom-trained LLMs

Custom-trained LLMs provide a compelling opportunity to elevate the capabilities of pre-trained LLMs, tailoring them to excel in specific tasks and domains. Fortunately, a wide range of pre-trained LLM models is readily available, serving as a solid foundation for various natural language processing tasks. While these pre-trained LLMs demonstrate a strong grasp of language understanding, their true potential is unlocked through custom training.

To illustrate this concept, let’s explore an example: Imagine a pre-trained LLM proficient in multiple languages, capable of translation, question-answering, and coherent text generation. While impressive, it lacks specialized knowledge in medical terminology and healthcare-related tasks. To address this limitation, developers embark on a fine-tuning journey, leveraging a vast dataset of medical literature, patient records, and clinical notes. Through this meticulous fine-tuning process, the LLM delves into the intricacies of medical language, unraveling complex jargon and immersing itself in the specific context of the healthcare domain. It becomes attuned to the nuances of medical diagnoses, treatments, and interactions, transforming into a specialized language expert within the medical field. Upon completion of custom training, the LLM undergoes a metamorphosis, emerging as a powerful medical language model. Armed with its newfound domain expertise, it now excels at accurately diagnosing medical conditions, summarizing research papers, generating patient reports, and even aiding healthcare professionals in making informed decisions. In this illuminating example, the custom-trained LLM evolves from a general language understanding model to a finely-tuned instrument, purpose-built to tackle specific medical challenges with remarkable precision and relevance. Just as a musician’s talent flourishes when they focus on mastering a particular genre, custom-trained LLMs flourish when tailored to specific applications, offering unparalleled performance and domain expertise.

Pros of Custom-trained LLMs

  • Improved Performance: Fine-tuning LLMs on task-specific datasets significantly enhances performance compared to generic pre-trained models. The model learns task-specific patterns and relationships, leading to better task completion and understanding.
  • Faster Training: Fine-tuning requires less training time and computational resources than training LLMs from scratch. This efficiency enables quicker model development and deployment, reducing time-to-market for applications.
  • Reduced Data Requirements: Fine-tuning LLMs on task-specific datasets demands significantly fewer data than training from scratch; while leveraging the general linguistic patterns learned from the pre-trained model, custom training adapts this knowledge to specific tasks, reducing the need for massive task-specific datasets.
  • Flexibility and Adaptability: Fine-tuned LLMs can be easily adapted to new tasks or domains, making it possible to reuse the model for various language-related challenges without starting the training process from scratch. Custom training allows developers to optimize the model for their intended task, improving performance.
  • Transfer Learning Benefits: Pre-trained LLMs serve as a valuable form of transfer learning. They capture a wide array of linguistic features and structures during pre-training, which can be transferred to various tasks with fine-tuning. This knowledge transfer improves the performance of custom-trained LLMs as they begin with a solid understanding of many aspects of language.
  • Reduced Carbon Footprint: Training LLMs from scratch consumes significant energy and contributes to carbon emissions. By reusing pre-trained models, custom training reduces the overall carbon footprint and computational waste associated with training large models multiple times.

Training Custom Large Language Models

  • Reduce Risk
  • Simplify Compliance
  • Gain Visibility
  • Version Comparison

Cons of Custom-trained LLMs

Custom-trained LLMs offer numerous advantages, but developers and researchers must consider certain drawbacks. One critical concern is data bias, where training LLMs on biased or limited datasets can lead to biased model outputs. To ensure ethical and unbiased performance, careful consideration of dataset composition and implementation of bias mitigation techniques are essential. Another potential issue is overfitting, where fine-tuned LLMs become too specialized on the task-specific dataset, resulting in subpar performance on unseen data. Overfitting can be managed through proper regularization and hyperparameter tuning.

Specifically, when building custom-trained LLMs upon proprietary or open-source pre-trained models, there are distinct disadvantages associated with each case.

Proprietary Pre-trained Models as Foundation

  • Cost and Licensing: Proprietary pre-trained models often come with expensive licensing fees, which may be prohibitive for small businesses, researchers, or individuals, limiting accessibility and hindering innovation in natural language processing.
  • Limited Customizability: Proprietary models might have restrictions on customization, preventing users from fine-tuning them to suit specific needs, such as modifying the architecture, adding domain-specific data, or adapting the model for niche applications.
  • Vendor Lock-in: Utilizing proprietary pre-trained models can lead to vendor lock-in, making it challenging for users to switch to other models or platforms in the future. This lack of portability can cause dependency and difficulty migrating to newer, more efficient models.
  • Privacy Concerns: Proprietary models may require sending sensitive data to the vendor’s servers for fine-tuning, raising privacy and security concerns, which might deter users from sharing sensitive information, especially in industries with strict data regulations.
  • Limited Support and Updates: The level of support and updates for proprietary models may vary, with some vendors prioritizing larger customers or specific industries. This can lead to delays in bug fixes, updates, and improvements.

Open-Source Pre-trained Models as Foundation:

  • Quality and Consistency: Open-source models can vary widely in quality and performance. Some models may not have undergone extensive testing or fine-tuning, leading to inconsistencies in results and reliability.
  • Lack of Warranty: Open-source pre-trained models typically come with no warranty or guaranteed support, which may cause difficulties in troubleshooting or obtaining assistance, especially for non-trivial problems.
  • Limited Functionality: Certain open-source pre-trained models might not cover all aspects of natural language understanding or specific tasks, resulting in suboptimal performance for certain use cases.
  • Data Bias: Open-source models trained on large, publicly available datasets can contain inherent biases in the data. Fine-tuning on proprietary datasets might not fully mitigate these biases, perpetuating unfair or harmful results.
  • Complex Deployment and Maintenance: Deploying and maintaining open-source models may require significant technical expertise, making them less accessible to users without a strong background in natural language processing or machine learning.
  • Compatibility and Interoperability: Different open-source models may have varying formats and requirements, leading to compatibility issues when integrating them into existing systems or pipelines.

Challenges of Custom-trained LLMs

Developing custom LLMs presents an array of challenges that can be broadly categorized under data, technical, ethical, and resource-related aspects.

  • Data Challenges: Acquiring domain-specific data can be difficult, particularly for niche or sensitive domains. Ensuring data quality during collection is essential for reliable model performance. Privacy and security concerns must be addressed when using proprietary or sensitive data, necessitating measures to de-identify and safeguard the data during training and deployment.
  • Technical Challenges: Building custom LLMs involves hurdles related to model architecture, training, evaluation, and validation. Selecting the appropriate architecture and parameters requires expertise, and training custom LLMs demands advanced machine-learning skills. Evaluating the model’s performance on domain-specific tasks can be complex due to the absence of established benchmarks. Additionally, validating the model’s responses for accuracy, safety, and compliance adds to the technical complexity.
  • Ethical Challenges: Ethical considerations are paramount when building custom LLMs. Bias and fairness issues may arise as LLMs can inadvertently perpetuate biases present in the training data. Ensuring the model outputs are fair and unbiased requires careful auditing and mitigation strategies. Moreover, content moderation and safety are critical concerns to prevent inappropriate or harmful content generated by custom LLMs, necessitating robust content filtering mechanisms.
  • Resource Challenges: Building custom LLMs demands significant computational resources and expertise. Training LLMs can be computationally expensive, making it costly for some individuals and organizations. Moreover, developing custom LLMs requires a skilled team with expertise in machine learning, natural language processing (NLP), and software engineering, which may be challenging to find and retain.

While these challenges may seem daunting, they can be overcome with proper planning, adequate resources, and the right expertise. As open-source foundation models become more available and commercially viable, the trend to build domain-specific LLMs using these foundation models is likely to increase. Custom-trained LLMs hold immense potential in addressing specific language-related challenges, and with responsible development practices, organizations can unlock their full benefits.

General workflow for custom training LLMs

If you are considering custom training an LLM, you must take several steps.

1. Identifying the Purpose and Scope of Your LLM:

Before embarking on custom training for your LLM, clearly defining its purpose and scope is crucial. Start by identifying the specific task or domain your LLM will serve. Whether it’s a question-answering system for a knowledge domain or another application, this definition will guide the entire development process. Once the task or domain is defined, analyze the data requirements for training your custom LLM. Consider the volume and quality of data needed for meaningful results. Assess the availability of domain-specific data; is it readily accessible, or will you need to collect and preprocess it yourself? Be mindful of potential data challenges, such as scarcity or privacy concerns. With the task and data analyzed, set clear objectives and performance metrics to measure the success of your custom LLM.

Establish the expected outcomes and the level of performance you aim to achieve, considering factors like language fluency, coherence, contextual understanding, factual accuracy, and relevant responses. Define evaluation metrics like perplexity, BLEU score, and human evaluations to measure and compare LLM performance. These well-defined objectives and benchmarks will guide the model’s development and assessment. This preliminary analysis ensures your LLM is precisely tailored to its intended application, maximizing its potential for accurate language understanding and aligning with your specific goals and use cases.

2. Data Collection and Preprocessing:

Data collection and preprocessing are critical in custom training LLMs. These steps ensure the model receives high-quality, relevant information, making it capable of accurate language understanding and providing meaningful outputs. To ensure the success of your custom LLM, it is essential to follow a comprehensive data collection and preprocessing process.

  • Data Collection: Begin by sourcing domain-specific text data from reputable and relevant sources. Look for datasets, text corpora, or domain-specific documents that align with the intended application of your custom LLM. The data should encompass real-world scenarios and cover various language patterns typical to the domain. High-quality data is crucial for the LLM to learn and generalize effectively.
  • Text Cleaning: The first step in preprocessing the collected data is text cleaning. It involves removing irrelevant information such as HTML tags, special characters, or non-textual elements that can disrupt the model’s understanding—additionally, correct spelling, typos, and grammar errors to avoid misinterpretation by the LLM. Converting the text to lowercase ensures uniformity in the data, as the model treats uppercase and lowercase words differently. Handling contractions (e.g., “won’t” to “will not”) helps avoid ambiguity in language and improves language processing. Removing duplicate sentences and instances from the dataset is essential to prevent the model from overfitting to repeated information. By eliminating redundancy, you ensure the model learns from diverse examples, enhancing its generalization capabilities.
  • Tokenization: Tokenization is a fundamental step in preparing the text data for LLM training. It involves breaking the text into smaller units, such as words or subwords, allowing the model to process them individually. Word-level tokenization splits the text into words, while subword tokenization divides it into smaller, more manageable units, capturing common word parts. Character tokenization can also be applied, which breaks text into individual characters.
  • Stop Words Removal: Stop words are commonly occurring words (e.g., “the,” “and,” “is”) that don’t contribute significantly to the meaning of the text and can be removed to reduce noise and the size of the vocabulary that the LLM needs to learn. Removing stop words can improve the model’s efficiency and prevent it from focusing on less informative terms.
  • Lemmatization and Stemming: Lemmatization and stemming are techniques to reduce words to their base or root form. Lemmatization provides more meaningful words compared to stemming. Both processes help the LLM to recognize different states of the same word as identical, improving its ability to grasp context and relationships between words.
  • Handling Special Cases: Certain languages or tasks may require specific preprocessing steps. For example, emoticons and emojis might need special handling in sentiment analysis. Ensure that the text data is appropriately processed to preserve these special characters’ meaning during LLM training.
  • Dealing with Outliers: Outliers in text data can negatively impact the LLM’s performance. Carefully handle such cases by removing them from the dataset or augmenting them to align with the overall data distribution. Ensuring the LLM learns from representative data will improve its robustness and generalization.
  • Handling Imbalanced Data (if applicable): In tasks like sentiment analysis or text classification, imbalanced datasets can cause a bias towards the majority class. Techniques like oversampling or undersampling can address this issue, ensuring the LLM learns from balanced data and avoids skewing results.
  • Padding and Truncation: LLMs typically work with fixed-length inputs, so text sequences may need to be padded with special tokens to ensure uniform length or truncated to a specific size. This ensures all input data is the same length, allowing efficient processing during training.
  • Data Formatting: Transform the preprocessed text data into a format compatible with the LLM’s training requirements, such as token IDs or numerical representations. This step prepares the data for input into the model during training.
  • Text annotation enriches text data by adding specific information, facilitating model training and comprehension. It varies based on NLP tasks, such as POS tagging, NER, sentiment analysis, dependency parsing, entity linking, text classification, topic modeling, and question-answering pairing. Human annotators or pre-existing datasets perform text annotation, requiring expertise for accurate and consistent results. The annotated data undergoes preprocessing, including tokenization and stemming, followed by word embedding, preparing it for custom LLM training.
  • Word Embeddings: Creating word embeddings is another crucial step that involves representing text tokens as continuous vectors in a vector space. These embeddings capture semantic relationships between words, allowing LLMs to better understand the contextual meaning of words and phrases.

It is essential to emphasize the importance of data privacy and security, particularly when dealing with sensitive information. If your data comprises sensitive details like personally identifiable data or proprietary documents, prioritizing data privacy and security is paramount. Take measures to anonymize or pseudonymize any sensitive data, safeguarding user privacy. Employ encryption and access controls to maintain data confidentiality during storage and training processes, ensuring that sensitive information remains secure. Moreover, validating data integrity and coherence is vital before feeding the preprocessed data into the LLM. Verify the consistency in labeling and ensure that the data accurately reflects the intended task or domain. Address any remaining inconsistencies or errors to safeguard against potential biases or misinformation that may impact the model’s training. By conducting thorough validation, you can instill confidence in the reliability and robustness of your custom LLM, elevating its performance and effectiveness.

3. Model selection and Architecture

Selecting the appropriate LLM architecture is a critical decision that profoundly impacts the custom-trained LLM’s performance and capabilities. Depending on the task’s complexity and dataset size, you can choose from various pre-existing LLM architectures like GPT, BERT, RoBERTa, or XLNet, or explore newer options if available. Creating a novel architecture is also possible but requires substantial NLP and deep learning expertise.

Several factors must be considered when evaluating the right architecture, regardless of whether it’s an open-source or paid model:

  • Model Size and Complexity: The LLM’s size and complexity should match the available computational resources and the intended application. Larger models offer higher language understanding abilities but require more computational power and memory. Smaller models may be preferable for resource-constrained environments or less computationally demanding tasks.
  • Domain Relevance: Consider the LLM architecture’s domain relevance. Some models are pre-trained on general language data, while others focus on specific biomedical, legal, or financial domains. Choose an architecture aligned with your task’s domain to benefit from domain-specific language understanding.
  • Community Support and Updates: Assess the level of community support and the frequency of updates for both open-source and paid LLMs. Active community support ensures timely bug fixes and continuous improvements, enhancing the model’s reliability and performance.
  • Cost and Licensing: Considering a paid LLM, weigh the cost against its benefits for your specific application. Review the licensing terms to align with your intended use and distribution requirements.
  • Ethical Considerations: Be mindful of ethical considerations related to LLM architectures. Some models may have biases in their pre-trained parameters, which could influence the custom-trained LLM’s outputs. Choose an architecture that promotes ethical use and fairness.
  • Integrability and Deployment: Consider how easily the LLM can be integrated into your existing infrastructure and deployed in your target application. A well-documented and developer-friendly architecture simplifies the integration process and reduces deployment time.
  • Model Performance on Similar Tasks: Evaluate the performance of different LLM architectures on similar tasks or benchmarks. This comparison helps gauge how well each architecture performs on tasks related to your application. Look for published results and user feedback to make an informed decision.

By thoroughly assessing these factors, you can make an informed choice that aligns the LLM architecture with your specific needs, maximizing its potential and ensuring effective language understanding for your custom-trained LLM.

4. Model training and evaluation

Before commencing the training process, divide the dataset into three subsets: training, validation, and test data. The training data optimizes the model’s parameters, the validation data tunes hyperparameters and prevents overfitting, and the test data objectively evaluates the model’s final performance. Select the appropriate training strategy based on the available data and task nature. Use supervised learning techniques for tasks with labeled data (e.g., classification, sentiment analysis) and unsupervised learning methods for tasks like text summarization or topic modeling. Choose hardware capable of efficiently handling the model’s size and complexity. High-performance GPUs or specialized hardware accelerators like TPUs can significantly speed up the process, reducing time and costs. After training, assess the model’s performance on the test dataset. Based on the results, fine-tuning may be required, such as adjusting hyperparameters, modifying the architecture, or monitoring for overfitting. Additional training with extra data might be necessary to boost performance. You can read more on Fine tuning a Pre-trained model here. By continually evaluating and refining the custom LLM through fine-tuning and iterative training, developers can develop powerful language models that excel at specific tasks and adapt to varying language contexts. These steps ensure that the LLM continuously evolves to meet the changing needs of the application and achieves the desired level of language understanding and performance. Evaluation and performance assessment are critical stages in custom training LLMs to ensure their effectiveness and reliability for specific tasks and domains. This phase involves defining evaluation metrics, conducting validation and testing, and interpreting the results to refine the model. For more information on LLM evaluation, you can find additional details here. Additionally, you can get Early Access to Deepchecks LLM Evaluation here.

5. Deployment and Monitoring

This stage involves integrating the custom LLM into real-world applications or systems and ensuring its ongoing performance and reliability. Integration requires setting up APIs or interfaces for data input and output, ensuring compatibility and scalability. Continuous monitoring tracks response times, error rates, and resource usage, enabling timely intervention. Regular updates and maintenance keep the LLM up-to-date with language trends and data changes. Ethical considerations involve monitoring for biases and implementing content moderation. Careful deployment and monitoring ensure seamless functioning, efficient scalability, and reliable language understanding for various tasks.


Training a custom LLM is a strategic process that involves careful planning, data collection, and preprocessing. Choosing the right LLM architecture and iterative fine-tuning ensure optimal performance and adaptation to real-world challenges. Monitoring and maintenance sustain the model’s reliability and address concept drift over time. LLM development presents exciting opportunities for innovation and exploration, leveraging open-source and commercial foundation models to create domain-specific LLMs. Encouraging further exploration in this field will advance natural language processing technology, revolutionizing industries and enhancing human-computer interaction. In conclusion, custom LLM training leads to specialized language models continuously evolving, offering exciting possibilities in natural language processing.


Training Custom Large Language Models

  • Reduce Risk
  • Simplify Compliance
  • Gain Visibility
  • Version Comparison

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