The Ultimate Guide to LLM Fine Tuning: Best Practices & Tools

What is model fine tuning and how can you fine-tune LLMs to serve your use case? Explore various Large Language Models fine tuning methods and learn about their benefits and limitations.

Armin Norouzi
December 4, 2023
September 13, 2023
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As users increasingly rely on Large Language Models (LLMs) to accomplish their daily tasks, their concerns about the potential leakage of private data by these models have surged.

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English to French Translation:

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Since the release of the groundbreaking paper “Attention is All You Need,” Large Language Models (LLMs) have taken the world by storm. Companies are now incorporating LLMs into their tech stack, using models like ChatGPT, Claude, and Cohere to power their applications.

This surge in popularity has created a demand for fine-tuning foundation models on specific data sets to ensure accuracy. Businesses can adapt pre-trained language models to their unique needs using fine tuning techniques and general training data. This has led to the rise of Generative AI and companies like OpenAI. The ability to fine tune LLMs has opened up a world of possibilities for businesses looking to harness the power of AI.

Here’s what we’ll cover:

  1. What is LLM fine tuning?
  2. How does fine tuning LLMs work?
  3. How to choose the best pre-trained model for fine-tuning?
  4. Large Language Models fine-tuning methods
  5. Challenges & limitations of LLM fine tuning
  6. Understanding LLM fine tuning: Resources & tools

Now, let’s get started.

What is LLM Fine-Tuning

Model fine tuning is a process where a pre-trained model, which has already learned some patterns and features on a large dataset, is further trained (or "fine tuned") on a smaller, domain-specific dataset. In the context of "LLM Fine-Tuning," LLM refers to a "Large Language Model" like the GPT series from OpenAI. This method is important because training a large language model from scratch is incredibly expensive, both in terms of computational resources and time. By leveraging the knowledge already captured in the pre-trained model, one can achieve high performance on specific tasks with significantly less data and compute.

When do we need to fine tune models

Fine-tuning models is crucial in machine learning when you want to adapt a pre-existing model to a specific task or domain. The decision to fine tune a model depends on your objectives, which are often domain or task-specific. Here are some key scenarios when you should consider fine-tuning:

  1. Transfer Learning: Fine-tuning is a key component of transfer learning, where a pre-trained model's knowledge is transferred to a new task. Instead of training a large model from scratch, you can start with a pre-trained model and fine tune it on your specific task. This accelerates the training process and allows the model to leverage its general language understanding for the new task.
  2. Limited Data Availability: Fine-tuning is particularly beneficial when you have limited labeled data for your specific task. Instead of training a model from scratch, you can leverage a pre-trained model's knowledge and adapt it to your task using a smaller dataset.
  3. Time and Resource Efficiency: Training a deep learning model from scratch requires substantial computational resources and time. Fine-tuning on top of a pre-trained model is often more efficient, as you can skip the initial training stages and converge faster to a solution.
  4. Task-Specific Adaptation: Fine-tuning is necessary when you have a pre-trained language model, and you want to adapt it to perform a specific task. For example, you might fine tune a language model for sentiment analysis or text generation for a particular domain like medical or legal documents using domain specific data.
  5. Continuous Learning: Fine-tuning is useful for continuous learning scenarios where the model needs to adapt to changing data and requirements over time. It allows you to periodically update the model without starting from scratch.
  6. Bias Mitigation: If you're concerned about biases present in a pre-trained model, fine-tuning can be used to reduce or counteract those biases by providing balanced and representative training data for the fine-tuning process.
  7. Data Security and Compliance: When working with sensitive data that cannot leave a specific environment due to security and compliance concerns, you might need to fine tune a model locally on your secure infrastructure. This ensures that the model never leaves your controlled environment while still being adapted to your task.

Benefits & applications of fine tuned models

In this section, we'll explore how fine-tuning can revolutionize various natural language processing tasks. As illustrated in the figure, we'll delve into key areas where fine-tuning can enhance your NLP application.

**💡 Pro tip: Want to learn more about In-context Learning? Head over to Lakera's guide on the topic to learn what ICL is and how it works. **

Let’s have a look:

  • Sentiment Analysis: If you're eager to enhance your sentiment analysis capabilities, consider fine-tuning the model to boost its performance in understanding and categorizing emotions and opinions in textual content.
  • Named Entity Recognition (NER): For tasks that involve pinpointing the names of individuals, organizations, locations, and various entities, fine-tuning the model can significantly enhance its precision and accuracy in recognizing and classifying these key elements.
  • Text Generation: Fine-tuning is a powerful tool for customizing the model's text generation abilities. This process allows you to mold the model's output to adhere to specific writing styles, tones, or themes, making it ideal for creative writing, content creation, and chatbot applications.
  • Translation: If you're in the business of building a translation system, consider fine-tuning the model for specific language pairs. This approach can elevate the quality and precision of translations, ensuring that your translations are top-notch.
  • Text Summarization: To develop effective summarization models, fine-tuning can be employed to train the language model in generating clear and concise summaries of lengthy texts, making it an invaluable asset for content summarization tasks.
  • Question Answering: When tackling tasks that require answering questions based on contextual information, fine-tuning is your ally. It equips the model with the ability to comprehend and extract relevant details, enabling it to provide accurate and context-aware responses.
  • Conversational Agents: Fine-tuning is essential for chatbots and conversational agents. It ensures that the model's responses remain contextually relevant and maintain a natural flow in conversations, delivering a seamless user experience.

**💡 Pro tip: Are you curious about the foundational principles behind models like GPT-3? Get a clear understanding with Lakera's Foundation Models Explained article. It's a deep dive into the core mechanics of today's leading LLMs.**

How does fine tuning Large Language Models work?

Fine-tuning is a crucial step in enhancing large language models (LLMs) through transfer learning. It involves adjusting an LLM's parameters with task-specific data, maintaining its original training knowledge. This allows models like BERT or GPT-4 to excel in specific tasks while preserving their language understanding. The fine-tuning process comprises two phases: preparation and fine-tuning. Also, various data training techniques encompass data synthesis, continual learning, transfer learning, one shot learning, few shot learning, and multi task learning, warranting careful consideration.

Preparation process

The preparation process involves getting the base pre-trained model ready for specific downstream tasks or domains. Here are the key steps involved in the preparation process:

  1. Select Pre-trained Model: Your first step is to carefully select a base pre-trained model that aligns with your desired architecture and functionalities. This pre-trained model, having been trained on a vast corpus of text, possesses a broad comprehension of language
  2. Define Task and Data: Clearly define the specific task you want the model to perform. Prepare a dataset that is relevant to your task. The dataset should be labeled or structured in a way that the model can learn from it.
  3. Data Augmentation: Depending on the task, data augmentation techniques may be applied to increase the diversity of the training data.

Model fine tuning process

Now, let's delve into the fine-tuning procedure. This is where we'll take that carefully prepared model and teach it to perform exceptionally well in the particular task we have in mind. In the figure below, you can see the key stages of the fine-tuning process, but it could be broken down in further steps and substeps. Let’s dive deeper:

Source: Scribble Data

Let’s dive deeper.

  1. Dataset Preprocess: In this first step, you ready your dataset for fine-tuning by cleaning it, splitting it into training, validation, and test sets, and ensuring it's compatible with the model. Proper data preparation is vital for the following steps.
  2. Model Initialization: You begin with a pre-trained LLM, such as GPT-3 or GPT-4, and initialize it with its pre-trained weights. This model has already learned a vast amount of knowledge from a broad range of text, making it a powerful starting point for fine-tuning.
  3. Task-Specific Architecture: To customize the model for your task, you can adjust its architecture by adding task-specific layers or modifying existing ones. These changes help the model specialize in your task while preserving its general language understanding capabilities from pre-training.
  4. Training: With the modified architecture in place, you train the model on your task-specific dataset. During training, the model's weights are updated through backpropagation and gradient descent based on the data provided. The model learns to recognize task-specific patterns and relationships within your dataset.
  5. Hyperparameter Tuning: Fine-tuning involves adjusting hyperparameters like the learning rate, batch size, and regularization strength to optimize the model's performance. Careful tuning helps ensure the model learns effectively and generalizes well to new data without overfitting.
  6. Validation: You monitor the model's performance on a separate validation dataset throughout the training process. This step helps you assess how well the model is learning the task and whether it's overfitting to the training data. If necessary, you can make adjustments based on the validation results.
  7. Testing: Once training is complete, you evaluate the model on a separate test dataset that it has never seen before. This step provides an unbiased measure of the model's performance and its ability to handle new, unseen data. It helps ensure that the model's performance is reliable in real-world scenarios.
  8. Iterative Process: Fine-tuning is often an iterative process. Based on the validation and test sets results, you may need to make further adjustments to the model's architecture, hyperparameters, or training data to improve its performance.
  9. Early Stopping: Implementing early stopping mechanisms is crucial to prevent overfitting. If the model's performance plateaus or degrades on the validation set, training can be halted to avoid further overfitting. This not only saves computational resources but also ensures the model's generalization ability.
  10. Deployment: After successful validation and testing, deploy the fine tuned model for real-world use, integrating it into software systems or services for tasks like text generation, answering questions, or recommendations.
  11. Add security measures: Implement robust security measures, including tools like Lakera, to protect your LLM and applications from potential threats and attacks. Regular security audits and updates are essential to maintain trustworthiness in real-world scenarios.

Fine-tuning is often an iterative process. After achieving satisfactory performance on the validation and test sets, it's crucial to implement robust security measures, including tools like Lakera, to protect your LLM and applications from potential threats and attacks.

How to choose the best pre-trained model for fine-tuning

Choosing the most suitable pre-trained language model (LLM) for fine-tuning is crucial in natural language processing tasks. This part will explore essential considerations and strategies to help you select the best pre-trained model that aligns with your specific fine-tuning objectives and requirements. Here are the steps we should take to choose the best pre-trained model:

  1. Task Definition: Begin by defining the task you intend your fine tuned model to excel at. Is it text generation, text classification, translation, summarization, or another specific NLP task? Clearly outlining your objective is the foundational step.
  2. Model Architecture Familiarization: Acquaint yourself with various pre-trained model architectures available in the NLP field. These may encompass GPT-3, BERT, RoBERTa, and many others. Gain insight into each architecture's distinctive features and characteristics concerning your task.
  3. Strengths and Weaknesses Assessment: Delve deeper into understanding the strengths and weaknesses of each model architecture. Analyze how well they perform regarding context comprehension, coherent text generation, handling lengthy documents, or any other crucial aspects pertinent to your task.
  4. Match with Task Requirements: Carefully evaluate the specific requirements of your task. Identify whether it necessitates understanding context, generating coherent and contextually appropriate text, handling extended text passages, or any other particular capabilities. Choose a pre-trained model that aligns closely with these essential prerequisites.

In addition to these steps, it is essential to consider various factors when selecting the optimal model. Here are the key considerations:

  • Model Size: Evaluate the model's size in terms of parameters. Larger models offer greater capacity to capture intricate patterns but demand more computational resources.
  • Available Checkpoints: Seek reputable sources for pre-trained model checkpoints. Official checkpoints from developers or well-vetted community-contributed versions are preferred.
  • Domain and Language: Ensure the pre-trained model aligns with your task's domain or language. Fine-tuning on a similar domain or language can enhance performance, particularly for tasks involving domain-specific terminology.
  • Pre-training Datasets: Investigate the datasets used for the model's pre-training. Models trained on extensive and diverse datasets generally exhibit a more comprehensive grasp of language.
  • Transfer Learning Capability: Assess the model's transfer learning aptitude. Some models excel in versatile task transfer, while others shine in specific domains.
  • Resource Constraints: Consider your available computational resources. Larger models necessitate more memory and processing power, both during fine-tuning and inference.
  • Fine-Tuning Documentation: Prioritize models for which clear fine-tuning guidelines or tutorials are available for your specific task. Proper documentation streamlines the fine-tuning process.
  • Bias Awareness: Be vigilant regarding potential biases in pre-trained models. If your task mandates unbiased predictions, opt for models tested and verified for bias and fairness.
  • Evaluation Metrics: Choose suitable evaluation metrics tailored to your task. For classification, accuracy may be pertinent, while language generation tasks might benefit from metrics like BLEU or ROUGE.

Large Language Models Fine Tuning Methods

Large Language Models (LLMs) Fine Tuning Methods encompass a variety of techniques, ranging from traditional, time-tested approaches to innovative, cutting-edge strategies, all aimed at enhancing the performance and applicability of these powerful models in diverse contexts.

Early Fine-tuning Methods / Old-school

In old-school approaches, there are various methods to fine tune pre-trained language models, each tailored to specific needs and resource constraints.

  1. Feature-based: It uses a pre-trained LLM as a feature extractor, transforming input text into a fixed-sized array. A separate classifier network predicts the text's class probability in NLP tasks. In training, only the classifier's weights change, making it resource-friendly but potentially less performant.
  2. Finetuning I: Finetuning I enhances the pre-trained LLM by adding extra dense layers. During training, only the newly added layers' weights are adjusted while keeping the pre-trained LLM weights frozen. It has shown slightly better performance than the feature-based approach in experiments.
  3. Finetuning II: In this approach, the entire model, including the pre-trained language model (LLM), is unfrozen for training, allowing all model weights to be updated. However, it may lead to catastrophic forgetting, where new features overwrite old knowledge. Finetuning II is resource-intensive but delivers superior results when maximum performance is needed.
  4. Universal Language Model Finetuning (ULMFiT): ULMFiT is a transfer learning method that can be applied to NLP tasks. It involves a 3-layer AWD-LSTM architecture for its representations. ULMFiT is a method for fine-tuning a pre-trained language model for a specific downstream task12.
  5. Gradient-based parameter importance ranking: These are methods used to rank the importance of features or parameters in a model. In gradient-based ranking, the importance of a parameter is determined by how much the accuracy decreases when the parameter is excluded. In Random Forest-based ranking, the impurity decrease from each feature can be averaged and the features are ranked according to this measure.

Cutting-edge strategies for LLM fine tuning

  1. Low Ranking Adaptation (LoRA): LoRA is a technique to fine tune large language models. It uses low-rank approximation methods to reduce the computational and financial costs of adapting models with billions of parameters, such as GPT-3, to specific tasks or domains.
  2. Quantized LoRA (QLoRA): QLoRA is an efficient finetuning approach for large language models (LLMs) that significantly reduces memory usage while maintaining the performance of full 16-bit finetuning. It achieves this by backpropagating gradients through a frozen, 4-bit quantized pretrained language model into Low Rank Adapters.
  3. Parameter Efficient Fine Tuning (PEFT): PEFT is an NLP technique that adapts pre-trained language models efficiently to various applications by fine-tuning only a small set of parameters, reducing computational and storage costs. It combats catastrophic forgetting, adjusting key parameters for specific tasks, and delivers comparable performance to full fine-tuning across modalities like image classification and stable diffusion dreambooth. It's a valuable approach for high performance with minimal trainable parameters.
  4. DeepSpeed: DeepSpeed is a deep learning software library that accelerates the training of large language models. It includes ZeRO (Zero Redundancy Optimizer), a memory-efficient approach for distributed training. DeepSpeed can automatically optimize fine-tuning jobs that use Hugging Face’s Trainer API, and offers a drop-in replacement script to run existing fine-tuning scripts.
  5. ZeRO: ZeRO is a set of memory optimization techniques that enable effective training of large models with trillions of parameters, such as GPT-2 and Turing-NLG 17B. A key appeal of ZeRO is that no model code modifications are required. It’s a memory-efficient form of data parallelism that gives you access to the aggregate GPU memory of all the GPU devices available to you, without inefficiency caused by the data replication in data parallelism.

**💡 Pro tip: Evaluating the performance and reliability of LLMs is paramount. Explore Lakera's insights on Large Language Model Evaluation to ensure your models deliver accurate and consistent results.**

Tools & best practices for fine-tuning LLMs

  1. ChatGPT 3.5 Fine-tuning turbo: Here, you can discover a prime method for fine-tuning LLMs with the upgraded GPT-3.5 Turbo model. Furthermore, this article offers straightforward Python code to assist developers in fine-tuning the model. Delve deeper to explore these updates, their advantages, and how to utilize them in your projects. [link]
  2. Efficient Fine-Tuning with LoRA/QLoRA: Businesses leverage advanced AI techniques and Large Language Models for text-related tasks. This blog explores efficient fine-tuning methods like QLoRA to generate product descriptions using the OpenLLaMA-3b-v2 model and the Red Dot Design Award Product Descriptions dataset. [link]

Challenges & limitations of LLM fine tuning

Some of the main challenges and limitations associated with fine-tuning LLMs:

  1. Overfitting: Fine-tuning can be prone to overfitting, a condition where the model becomes overly specialized on the training data and performs poorly on unseen data. This risk is particularly pronounced when the task-specific dataset is small or not representative of the broader context.
  2. Catastrophic Forgetting: During fine-tuning for a specific task, the model may forget previously acquired general knowledge. This phenomenon, known as catastrophic forgetting, can impair the model's adaptability to diverse tasks.
  3. Bias Amplification: Pre-trained models inherit biases from their training data, which fine-tuning can inadvertently amplify when applied to task-specific data. This amplification may lead to biased predictions and outputs, potentially causing ethical concerns.
  4. Generalization Challenges: Ensuring that a fine tuned model generalizes effectively across various inputs and scenarios is challenging. A model that excels in fine-tuning datasets may struggle when presented with out-of-distribution data.
  5. Data Requirements: Fine-tuning necessitates task-specific labelled data, which may not always be available or clean. Inadequate or noisy data can negatively impact the model's performance and reliability.
  6. Hyperparameter Tuning Complexity: Selecting appropriate hyperparameters for fine-tuning can be intricate and time-consuming. Poor choices may result in slow convergence, overfitting, or suboptimal performance.
  7. Domain Shift Sensitivity: Fine-tuning data significantly different from the pre-training data can lead to domain shift issues. Addressing this problem often requires domain adaptation techniques to bridge the gap effectively.
  8. Ethical Considerations: Fine tuned large language models may inadvertently generate harmful or inappropriate content, even when designed for benign tasks. Ensuring ethical behaviour and safety is an ongoing challenge, necessitating responsible AI practices.
  9. Resource Intensiveness: Fine-tuning large models demands substantial computational resources and time, posing challenges for smaller teams or organizations with limited infrastructure and expertise.
  10. Unintended Outputs: Fine-tuning cannot guarantee that the model consistently produces correct or sensible outputs. It may generate plausible but factually incorrect responses, requiring vigilant post-processing and validation.
  11. Model Drift: Over time, a fine tuned model's performance can deteriorate due to changes in data distribution or the evolving environment. Regular monitoring and re-fine-tuning may become necessary to maintain optimal performance and adapt to evolving conditions.

Understanding fine tuning LLMs: Resources & Tools

Here you can see some practical resources on fine tunning LLMs.

  1. How to use PEFT to fine tune any decoder-style GPT model [link]
  2. Efficient Fine-Tuning for Llama-v2-7b on a Single GPU [link] [link]

Here are some important tools and techniques for fine-tuning Large Language Models (LLMs):

  1. Hugging Face Transformers Library: This library is popular for working with transformer models like BERT, GPT-3, and others. It provides pre-trained models and utilities for fine-tuning them on your specific task.
  2. DeepSpeed: Developed by Microsoft, DeepSpeed is a deep learning optimization library that can accelerate fine-tuning, especially for large language models.
  3. PyTorch: PyTorch is a widely used open-source machine learning library. You can use PyTorch to fine tune a large language model like BERT.
  4. Databricks: Databricks is a platform that provides cloud-based big data processing using Apache Spark. It can be used to fine tune large language models.
  5. Simform's Guide: Simform provides a comprehensive guide on fine-tuning large language models, covering fundamentals, training data methodologies, strategies, and best practices.
  6. Lakera: To safeguard your LLM and applications from potential threats and attacks, it's crucial to establish strong security measures, such as utilizing tools like Lakera.

**💡 Pro tip: Crafting effective prompts is an art and a science. Enhance your LLM's performance with Lakera's Prompt Engineering Guide. Learn the strategies to guide your model's chain of thought effectively.**


In 2023, Large Language Models (LLMs) like GPT-4 have become integral to various industries, with companies adopting models such as ChatGPT, Claude, and Cohere to power their applications. Businesses are increasingly fine-tuning these foundation models to ensure accuracy and task-specific adaptability.

Fine-tuning allows them to customize pre-trained models for specific tasks, making Generative AI a rising trend. This article explored the concept of LLM fine-tuning, its methods, applications, and challenges. It also guided the reader on choosing the best pre-trained model for fine-tuning and emphasized the importance of security measures, including tools like Lakera, to protect LLMs and applications from threats.

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Armin Norouzi
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