Fine-Tuning LLMs: Top 6 Methods, Challenges & Best Practices

What Does It Mean to Fine-Tune LLMs?

Fine-tuning Large Language Models (LLMs) involves adjusting pre-trained models on specific datasets to enhance performance for particular tasks. This process begins after general training ends. Users provide the model with a more focused dataset, which may include industry-specific terminology or task-focused interactions, with the objective of helping the model generate more relevant responses for a specific use case.

Fine-tuning allows the model to adapt its pre-existing weights and biases to fit specific problems better. This results in improved accuracy and relevance in outputs, making LLMs more effective in practical, specialized applications than their broadly trained counterparts. While fine-tuning can be highly computationally intensive, new techniques like Parameter-Efficient Fine-Tuning (PEFT) are making it much more efficient and possible to run even on consumer hardware.

Fine-tuning can be performed both on open source LLMs, such as Meta LLaMA and Mistral models, and on some commercial LLMs, if this capability is offered by the model’s developer. (Learn more in our detailed guide to fine tuning Llama 2). For example, OpenAI allows fine tuning for GPT-3.5 and GPT-4. This is part of an extensive series of guides about machine learning.

Fine-Tuning vs. Embeddings vs. Prompt Engineering

Fine-tuning is a method where a pre-trained model is further trained (or fine tuned) on a new dataset specific to a particular task. This technique involves adjusting the weights across all layers of the model, based on the new data. It allows the model to specifically cater to nuanced tasks and often results in higher performance for specialized applications.

Embeddings refer to dense vector representations of words or phrases, which are typically obtained during the initial training of a model. Instead of adjusting the entire model, embeddings can be extracted and used as static input features for various downstream tasks. This approach does not modify the pre-trained model but leverages the learned representations. It’s generally faster and less resource-intensive than fine-tuning.

Prompt engineering is another way to adjust LLMs to specific tasks. Adding more context, examples, or even entire documents and rich media, to LLM prompts can cause models to provide much more nuanced and relevant responses to specific tasks. Prompt engineering is considered more limited than fine-tuning, but is also much less technically complex and is not computationally intensive.

Learn more in our detailed guide to LLM fine tuning vs embedding (coming soon)

When Does Your Business Need a Fine-Tuned Model?

Here are a few primary use cases for fine-tuned LLMs:

Specificity and Relevance

A fine-tuned model excels in providing highly specific and relevant outputs tailored to your business’s unique needs. Unlike general models, which offer broad responses, fine-tuning adapts the model to understand industry-specific terminology and nuances. This can be particularly beneficial for specialized industries like legal, medical, or technical fields where precise language and contextual understanding are crucial.

Improved Accuracy

Fine-tuning significantly enhances the accuracy of a language model by allowing it to adapt to the specific patterns and requirements of your business data. When a model is fine-tuned, it learns from a curated dataset that mirrors the particular tasks and language your business encounters. This focused learning process refines the model’s ability to generate precise and contextually appropriate responses, reducing errors and increasing the reliability of the outputs.

Data Privacy and Security

In many industries, maintaining data privacy and security is paramount. By fine-tuning a language model on proprietary or sensitive data, businesses can ensure that their unique datasets are not exposed to third-party risks associated with general model training environments. Fine-tuning can be conducted on-premises or within secure environments, keeping data control in-house.

Customized Interactions

Businesses that require highly personalized customer interactions can significantly benefit from fine-tuned models. These models can be trained to understand and respond to customer queries with a level of customization that aligns with the brand’s voice and customer service protocols. For instance, a fine-tuned model in a retail business can understand product-specific inquiries, offer personalized recommendations, understand company policies, and handle complex service issues more effectively than a general model.

Top 6 LLM Fine-Tuning Methods

Here are some of the ways that large language models can be fine tuned.

1. Instruction Fine-Tuning

Instruction fine-tuning involves training a model using examples that demonstrate how it should respond to specific queries. For instance, to improve summarization skills, a dataset with instructions like "summarize this text" followed by the actual text is used.

This method helps the model learn to follow specific instructions and improve its performance in targeted tasks by understanding the expected outputs from given prompts. This approach is particularly useful for enhancing the model’s ability to handle various task-specific instructions effectively.

2. Parameter-Efficient Fine-Tuning (PEFT)

PEFT updates only a small subset of the model’s parameters during training, significantly reducing the memory and computational requirements compared to full fine-tuning. Techniques like LoRA (Low-Rank Adaptation) and QLoRA (Quantized Low-Rank Adaptation) can reduce the number of trainable parameters by thousands of times.

This method helps manage hardware limitations and prevents the phenomenon of ‘catastrophic forgetting’, maintaining the model’s original knowledge while adapting to new tasks. By focusing on specific components, PEFT makes the fine-tuning process more efficient and cost-effective, especially for large models.

3. Task-Specific Fine-Tuning

Task-specific fine-tuning focuses on adjusting a pre-trained model to excel in a particular task or domain using a dedicated dataset. This method typically requires more data and time than transfer learning but achieves higher performance in specific tasks, such as translation or sentiment analysis.

Despite its effectiveness, it can lead to catastrophic forgetting, where the model loses proficiency in tasks it was previously trained on. However, by tailoring the model to specific requirements, task-specific fine-tuning ensures high accuracy and relevance for specialized applications.

4. Transfer Learning

Transfer learning leverages a model trained on a broad, general-purpose dataset and adapts it to specific tasks using task-specific data. This method is useful when data or resources are limited, as it builds on the knowledge already embedded in the pre-trained model, offering improved learning rates and accuracy with less training time compared to training from scratch.

Transfer learning enables the efficient reuse of models like GPT or BERT for new applications, providing a strong foundation for further customization.

Learn more in our detailed guide to fine tuning vs transfer learning (coming soon)

5. Multi-Task Learning

Multi-task learning trains a model on a dataset containing examples for multiple tasks, such as summarization, code translation, and entity recognition. This approach helps the model improve performance across different tasks simultaneously and avoids catastrophic forgetting.

However, this method requires a large amount of diverse data, which can be challenging to assemble. The comprehensive training enables the model to handle various tasks proficiently, making it suitable for environments where versatile performance is necessary.

6. Sequential Fine-Tuning

Sequential fine-tuning adapts a model to a series of related tasks in stages. For example, a general language model might first be fine-tuned for medical language and subsequently for pediatric cardiology. This method ensures the model retains its performance across various specialized domains, building on each successive fine-tuning step to refine its capabilities further.

By sequentially adapting to increasingly specific datasets, the model can achieve high proficiency in niche areas while maintaining a broad understanding of the general domain.

What Is Retrieval Augmented Generation (RAG)?

Retrieval Augmented Generation (RAG) is a technique that combines natural language generation with information retrieval to enhance a model’s outputs with up-to-date and contextually relevant information. RAG integrates external knowledge sources, ensuring that the language model provides accurate and current responses. This method is particularly useful for tasks requiring precise, timely information, as it allows continuous updates and easy management of the knowledge base, avoiding the rigidity of traditional fine-tuning methods.

RAG systems can dynamically retrieve information during generation, making them highly adaptable to changing data and capable of delivering more relevant and informed outputs. This technique is beneficial for applications where the accuracy and freshness of information are critical, such as customer support, content creation, and research. By leveraging RAG, businesses can ensure their language models remain current and provide high-quality responses that are well-grounded in the latest information available.

Notable examples of the use of RAG are the AI Overviews feature in Google search, and Microsoft Copilot in Bing, both of which extract data from a live index of the Internet and use it as an input for LLM responses.

How to Choose a Pre-Trained Model for Fine-Tuning

Here’s an overview of the process of identifying an existing LLM for fine-tuning.

Define the Task

Before fine-tuning, clearly define the model’s intended task. Understanding the task’s requirements helps in selecting a model whose pre-trained capabilities align closely with the end objectives. For example, it may involve classification, regression, or generative tasks.

An accurate task definition also aids in determining the necessary data scope for model fine-tuning. This can prevent potential performance degradation due to underfitting or overfitting during the fine-tuning phase.

Understand the Model Architecture

Get familiar with different model architectures to select the most suitable one for your task. Each architecture has strengths and limitations based on its design principles, layers, and the type of data it was initially trained on.

Understanding these characteristics can significantly impact the success of fine-tuning, as certain architectures might be more compatible with the nature of your specific tasks.

Assess Strengths and Weaknesses

Evaluate the strengths and weaknesses of the model options. Some models may excel at handling text-based tasks while others may be optimized for voice or image recognition tasks. Standardized benchmarks, which you can find on LLM leaderboards, can help compare models on parameters relevant to your project.

Additionally, consider the model’s performance trade-offs such as accuracy, processing speed, and memory usage, which can affect the practical deployment of the fine tuned model in real-world applications.

Match with Task Requirements

Ensure the pre-trained model’s capabilities match the demands of the task. This involves comparing the model’s training data, learning capabilities, and output formats with what’s needed for your use case. A close match between the model’s training conditions and your task’s requirements can enhance the effectiveness of the re-training process.

Related content: Read our guide to fine tuning LLM tutorial (coming soon)

Challenges and Limitations of LLM Fine-Tuning

Here are some of the challenges involved in fine-tuning large language models.

Overfitting

Overfitting occurs when a model is trained so closely to the nuances of a specific dataset that it performs exceptionally well on that data but poorly on any data it hasn’t seen before. This is particularly problematic in fine-tuning because the datasets used are generally smaller and more specialized than those used in initial broad training phases.

Such datasets can include rare or unique examples that do not represent a broader population, causing the model to learn these as common features. Overfitting results in a model that lacks the ability to generalize, which is critical for practical applications where the input data may vary significantly from the training data.

Catastrophic Forgetting

Catastrophic forgetting refers to a situation where a neural network, after being fine-tuned with new data, loses the information it had learned during its initial training. This challenge is especially significant in the fine-tuning of LLMs because the new, task-specific training can override the weights and biases that were useful across more general contexts.

For example, a model trained initially on a broad range of topics might lose its ability to comprehend certain general concepts if it is intensely retrained on a niche subject like legal documents or technical manuals.

Bias Amplification

Bias amplification is when inherent biases in the pre-trained data are intensified. During fine-tuning, a model may not only reflect but also exacerbate biases present in the new training dataset.

For example, if a dataset for fine-tuning an LLM on job application reviews contains biases against certain demographic groups, the model might amplify this bias, leading to discriminatory behavior in automated screening processes. This underscores the need for careful selection of datasets to avoid reinforcing harmful stereotypes or unfair practices in model outputs.

Hyperparameter Tuning Complexity

Hyperparameters, such as learning rate, batch size, and the number of epochs during which the model is trained, have a major impact on the model’s performance. These parameters need to be carefully adjusted to strike a balance between learning efficiently and avoiding overfitting. The optimal settings for hyperparameters vary between different tasks and datasets.

The process of identifying the right hyperparameter settings is time-consuming and computationally expensive, requiring extensive use of resources to run numerous training cycles. However, standardized methods, frameworks, and tools for LLM tuning are emerging, which aim to make this process easier.

LLM Fine-Tuning Best Practices

Here are some of the measures you can take to ensure an effective LLM fine-tuning process.

Start with a Small Model

Beginning with a smaller model can simplify the fine-tuning process. Smaller models require less computational power and memory, allowing for faster experimentation and iteration. This approach is particularly beneficial when resources are limited. Once the process is optimized on a smaller scale, the insights gained can be applied to fine-tune larger models.

Experiment with Different Data Formats

Experimenting with various data formats can significantly enhance the effectiveness of fine-tuning. By including diverse input types—such as structured data, unstructured text, images, or even tabular data—models can learn to handle a broader range of real-world scenarios. This helps build versatility in the model’s responses, ensuring it performs well across different contexts and input variations.

Start with Subsets of Data

Starting with fine-tuning on smaller subsets of the dataset allows for quicker iterations and helps identify potential issues early in the training process. By gradually scaling up to the full dataset, you can fine-tune hyperparameters and make necessary adjustments without expending excessive resources.

Ensure the Dataset Is High-Quality

The dataset should be representative of the specific task and domain to ensure the model learns the relevant patterns and nuances. High-quality data minimizes noise and errors, allowing the model to generate more accurate and reliable outputs. Investing time in curating and cleaning the dataset ensures improved model performance and generalization capabilities.

Use Hyperparameters to Optimize Performance

Hyperparameter tuning is vital for optimizing the performance of fine-tuned models. Key parameters like learning rate, batch size, and the number of epochs must be adjusted to balance learning efficiency and overfitting prevention. Systematic experimentation with different hyperparameter values can reveal the optimal settings, leading to improvements in model accuracy and reliability.

Building LLM Applications with Acorn

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Fine-Tuning LLMs: Top 6 Methods, Challenges and Best Practices

June 6, 2024 by acorn-labs