Mastering the Art of Building an LLM from Scratch: A Step-by-Step Guide

Are you ready to embark on an epic journey to build your very own Large Language Model (LLM) from scratch? Buckle up, because we’re about to dive into the captivating world of custom LLMs! Whether you’re a tech enthusiast, a language lover, or just someone looking to expand their digital horizons, this blog post is for you. We’ll unravel the mysteries behind LLM development, explore the key steps involved, and even sprinkle in some humor along the way. So, grab your favorite caffeinated beverage and get ready to unleash your inner language wizard – because we’re about to learn how to build an LLM from scratch!

Understanding the Need for Custom Large Language Models (LLMs)

Imagine a time when training massive language models was the sole preserve of a select group of AI researchers, a realm so esoteric that few dared to venture. Then came the ground-breaking ChatGPT, and suddenly, the landscape shifted.

The allure of its capabilities sparked a wave of enthusiasm, and organizations worldwide began recognizing the potential in developing their own custom large language models.

But while the excitement is palpable, it’s crucial to understand that creating a custom LLM is akin to embarking on a considerable expedition. It’s not a journey for the faint-hearted. The process requires a formidable team of machine learning engineers, data scientists, and data engineers.

Additionally, the financial commitment is substantial – a model with ~10 billion parameters can cost about $150,000 to train, and a model with ~100 billion parameters? That could set you back by ~$1,500,000!

Before diving into this venture, it’s essential to assess whether your use-case truly necessitates a custom LLM. Often, pre-trained models or smaller custom models can effectively meet your needs.

Remember, LLMs are usually a starting point for AI solutions, not the end product. They form the foundation, and additional fine-tuning is almost always necessary to meet specific use-cases.

The world of LLMs is enticing, offering the promise of advanced AI solutions. But as with any significant investment, a careful evaluation of the need for a custom model is imperative. After all, in the realm of AI and LLMs, one size certainly doesn’t fit all.

Key Steps in Model Development

Imagine you’re about to embark on a journey to build a skyscraper. The success of such a colossal project doesn’t just depend on the skill of the architect but also on the quality of the materials used. Similarly, the construction of a custom Large Language Model (LLM), such as GPT-3 175b or Llama 70b, relies on four integral steps: data collection, data preprocessing, model architecture design, and model training. Just as the integrity of a skyscraper depends on the quality of its materials, the efficacy of your LLM hinges on the quality of its training data.

Data Collection

Imagine the internet as a vast quarry teeming with raw materials for your LLM. It offers a wide array of text sources, akin to various types of stones and metals, such as web pages, books, scientific articles, codebases, and conversational data. Harnessing these diverse sources is akin to mining different materials to give your skyscraper strength and durability. This diversity in training data, which can be fetched from open datasets like Common Crawl, Colossal Clean Crawled Corpus (C4), Falcon RefinedWeb, and The Pile, enhances the model’s ability to generalize across many tasks.

Data Preprocessing

But raw materials alone aren’t enough to build a skyscraper. They need to be refined and processed. Similarly, your collected data needs to be preprocessed.

This involves quality filtering to remove low-quality text, de-duplication to avoid instances of the same or similar text, privacy redaction to protect identifiable information, and tokenization to translate the data into a numerical form that your neural network can understand.

It’s akin to purifying and shaping the raw materials to make them fit for construction.

Model Architecture Design

Now, with your refined materials at hand, it’s time to design the architecture of your skyscraper. In the LLM world, Transformers represent the state-of-the-art architectural blueprint. These models, equipped with attention mechanisms, are akin to the core pillars of your skyscraper, linking inputs and outputs. Transformers feature two key modules: an encoder and a decoder, and come in three variations: Encoder-only, Decoder-only, and Encoder-Decoder.

The choice of variation depends on the specific task you want your LLM to perform. Other vital design elements include Residual Connections (RC), Layer Normalization (LN), Activation functions (AFs), and Position embeddings (PEs).

Model Training

With the blueprint ready and materials at hand, it’s time to start construction, or in the case of LLMs, training. You’ll need to balance training time, dataset size, and model size, much like a construction manager balances time, materials, and manpower. Techniques like mixed precision training, 3D parallelism, and Zero Redundancy Optimizer (ZeRO) can be used to streamline this process. The choice of batch size, learning rate, optimizer, and dropout rate are key variables that control the pace and efficiency of your construction project, or in our case, model training.

Remember, building a custom LLM from scratch is a journey. It’s akin to constructing a skyscraper, requiring careful planning, quality materials, and a skilled team. But with the right approach, it’s a journey that can lead to the creation of a model as remarkable as the world’s tallest skyscraper.

Model Evaluation: The Litmus Test for Your LLM

Building a model is akin to shaping raw clay into a beautiful sculpture. However, the true test of its worth lies not merely in its creation, but rather in its evaluation. This phase is of paramount importance in the iterative process of model development. The task set for model evaluation, often considered the crucible where the mettle of your LLM is tested, hinges heavily on the intended application of the model.

Imagine that you’ve painstakingly crafted your custom LLM, feeding it with a banquet of data and meticulously shaping its architecture. Now, you’re ready to unveil it to the world. But how do you measure its success? This is where model evaluation comes into play, serving as the yardstick to assess your model’s performance and efficacy.

One platform that provides a competitive arena for open-access LLMs is the Open LLM leaderboard hosted by Hugging Face. This leaderboard offers a general ranking based on the performance on four benchmark datasets: ARC, HellaSwag, MMLU, and TruthfulQA. Picture it as a grand stage where LLMs from all corners of the globe strut their stuff, vying for the top spot.

However, evaluating a model’s prowess isn’t solely about leaderboard rankings. For open-ended tasks, a more nuanced approach is necessary. This could involve manual human evaluation, using a spectrum of NLP metrics, or even employing a fine-tuned LLM. The choice of evaluation method, much like choosing the right lens for a camera, is contingent upon what you wish to focus on during the evaluation.

In the dynamic world of LLMs, where every model is unique, there is no one-size-fits-all evaluation method. Instead, it requires a judicious blend of the right evaluation tasks, metrics, and benchmark datasets to truly gauge the potency of your custom LLM.


Imagine standing at the base of an imposing mountain, gazing upward at its towering peak. That’s akin to the monumental task of building a large language model (LLM) from scratch. It’s a complex, intricate process that demands a significant investment of time, resources, and, most importantly, expertise. Much like a mountain expedition, it requires careful planning, precise execution, and a deep understanding of the landscape.

There are instances where some applications might thrive better with a custom-built LLM, just as some climbers prefer to carve their own path to the summit. However, in numerous cases, opting for an off-the-shelf model can be like taking a well-trodden trail – it may suffice for reaching the top without the added effort of paving a new path.

Every step of the way, you need to continually assess the potential benefits that justify the investment in building a large language model. It’s similar to a mountaineer constantly evaluating the risk versus reward of each move. In the world of non-research applications, this balance is crucial. The potential upside must outweigh the cost, justifying the effort, time, and resources poured into the project.

Regardless of whether you choose to blaze your own trail or follow an established one, the development of an LLM is an iterative process. It requires a deep understanding of multiple stages – data collection, preprocessing, model architecture design, training, and evaluation. These are the stepping stones that lead to the summit, each one as vital as the other.

So, as you embark on your journey to build an LLM from scratch, remember that reaching the peak is not the end. It’s an ongoing journey of refining, evaluating, and improving. The mountain of language modeling is always evolving, and so should your approach to conquering it.

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DeepAI is a Generative AI (GenAI) enterprise software company focused on helping organizations solve the world’s toughest problems. With expertise in generative AI models and natural language processing, we empower businesses and individuals to unlock the power of AI for content generation, language translation, and more.

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