How do LLMs work? It’s a question that sits at the heart of modern AI innovation. From writing assistants and chatbots to code generators and search engines, large language models (LLMs) are transforming the way machines interact with human language. Every time you type a prompt into ChatGPT or any other LLM-based tool, you’re initiating a complex pipeline of mathematical and neural processes that unfold within milliseconds.
In this post, we’ll break down exactly how LLMs work, exploring every critical stage, tokenization, embedding, transformer architecture, attention mechanisms, inference, and output generation. Whether you’re an AI engineer, data scientist, or tech-savvy reader, this guide is your comprehensive roadmap to the inner workings of LLMs.
What Is a Large Language Model?
A large language model (LLM) is a deep neural network trained on vast amounts of text data to understand and generate human-like language. These models are the engine behind AI applications such as ChatGPT, Claude, LLaMA, and Gemini. But to truly grasp how LLMs work, you need to understand the architecture that powers them: the transformer model.
Key Characteristics of LLMs:
- Built on transformer architecture
- Trained on large corpora using self-supervised learning
- Capable of understanding context, semantics, grammar, and even logic
- Scalable and general-purpose, making them adaptable across tasks and industries
Learn more about LLMs and their applications.
Why It’s Important to Understand How LLMs Work
LLMs are no longer just research experiments, they’re tools being deployed in real-world settings across finance, healthcare, customer service, education, and software development. Knowing how LLMs work helps you:
- Design better prompts
- Choose the right models for your use case
- Understand their limitations
- Mitigate risks like hallucinations or bias
- Fine-tune or integrate LLMs more effectively into your workflow
Now, let’s explore the full pipeline of how LLMs work, from input to output.
7 Best Large Language Models (LLMs) You Must Know About
Step-by-Step: How Do LLMs Work?
Step 1: Tokenization – How do LLMs work at the input stage?
The first step in how LLMs work is tokenization. This is the process of breaking raw input text into smaller units called tokens. Tokens may represent entire words, parts of words (subwords), or even individual characters.
Tokenization serves two purposes:
- It standardizes inputs for the model.
- It allows the model to operate on a manageable vocabulary size.
Different models use different tokenization schemes (Byte Pair Encoding, SentencePiece, etc.), and understanding them is key to understanding how LLMs work effectively on multilingual and domain-specific text.
Step 2: Embedding – How do LLMs work with tokens?
Once the input is tokenized, each token is mapped to a high-dimensional vector through an embedding layer. These embeddings capture the semantic and syntactic meaning of the token in a numerical format that neural networks can process.
However, since transformers (the architecture behind LLMs) don’t have any inherent understanding of sequence or order, positional encodings are added to each token embedding. These encodings inject information about the position of each token in the sequence, allowing the model to differentiate between “the cat sat on the mat” and “the mat sat on the cat.”
This combined representation—token embedding + positional encoding—is what the model uses to begin making sense of language structure and meaning. During training, the model learns to adjust these embeddings so that semantically related tokens (like “king” and “queen”) end up with similar vector representations, while unrelated tokens remain distant in the embedding space.
Step 3: Transformer Architecture – How do LLMs work internally?
At the heart of how LLMs work is the transformer architecture, introduced in the 2017 paper “Attention Is All You Need.” The transformer is a sequence-to-sequence model that processes entire input sequences in parallel—unlike RNNs, which work sequentially.
Key Components:
- Multi-head self-attention: Enables the model to focus on relevant parts of the input.
- Feedforward neural networks: Process attention outputs into meaningful transformations.
- Layer normalization and residual connections: Improve training stability and gradient flow.
The transformer’s layered structure, often with dozens or hundreds of layers—is one of the reasons LLMs can model complex patterns and long-range dependencies in text.
Step 4: Attention Mechanisms – How do LLMs work to understand context?
If you want to understand how LLMs work, you must understand attention mechanisms.
Attention allows the model to determine how much focus to place on each token in the sequence, relative to others. In self-attention, each token looks at all other tokens to decide what to pay attention to.
For example, in the sentence “The cat sat on the mat because it was tired,” the word “it” likely refers to “cat.” Attention mechanisms help the model resolve this ambiguity.
Types of Attention in LLMs:
- Self-attention: Token-to-token relationships within a single sequence.
- Cross-attention (in encoder-decoder models): Linking input and output sequences.
- Multi-head attention: Several attention layers run in parallel to capture multiple relationships.
Attention is arguably the most critical component in how LLMs work, enabling them to capture complex, hierarchical meaning in language.
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Step 5: Inference – How do LLMs work during prediction?
During inference, the model applies the patterns it learned during training to generate predictions. This is the decision-making phase of how LLMs work.
Here’s how inference unfolds:
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The model takes the embedded input sequence and processes it through all transformer layers.
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At each step, it outputs a probability distribution over the vocabulary.
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The most likely token is selected using a decoding strategy:
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Greedy search (pick the top token)
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Top-k sampling (pick from top-k tokens)
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Nucleus sampling (top-p)
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The selected token is fed back into the model to predict the next one.
This token-by-token generation continues until an end-of-sequence token or maximum length is reached.
Step 6: Output Generation – From Vectors Back to Text
Once the model has predicted the entire token sequence, the final step in how LLMs work is detokenization—converting tokens back into human-readable text.
Output generation can be fine-tuned through temperature and top-p values, which control randomness and creativity. Lower temperature values make outputs more deterministic; higher values increase diversity.
How to Tune LLM Parameters for Optimal Performance
Prompt Engineering: A Critical Factor in How LLMs Work
Knowing how LLMs work is incomplete without discussing prompt engineering—the practice of crafting input prompts that guide the model toward better outputs.
Because LLMs are highly context-dependent, the structure, tone, and even punctuation of your prompt can significantly influence results.
Effective Prompting Techniques:
- Use examples (few-shot or zero-shot learning)
- Give explicit instructions
- Set role-based context (“You are a legal expert…”)
- Add delimiters to structure content clearly
Mastering prompt engineering is a powerful way to control how LLMs work for your specific use case.
Learn more about prompt engineering strategies.
How Do LLMs Work Across Modalities?
While LLMs started in text, the principles of how LLMs work are now being applied across other data types—images, audio, video, and even robotic actions.
Examples:
- Code generation: GitHub Copilot uses LLMs to autocomplete code.
- Vision-language models: Combine image inputs with text outputs (e.g., GPT-4V).
- Tool-using agents: Agentic AI systems use LLMs to decide when to call tools like search engines or APIs.
Understanding how LLMs work across modalities allows us to envision their role in fully autonomous systems.
Explore top LLM use cases across industries.
Summary Table: How Do LLMs Work?
Frequently Asked Questions
Q1: How do LLMs work differently from traditional NLP models?
Traditional models like RNNs process inputs sequentially, which limits their ability to retain long-range context. LLMs use transformers and attention to process sequences in parallel, greatly improving performance.
Q2: How do embeddings contribute to how LLMs work?
Embeddings turn tokens into mathematical vectors, enabling the model to recognize semantic relationships and perform operations like similarity comparisons or analogy reasoning.
Q3: How do LLMs work to generate long responses?
They generate one token at a time, feeding each predicted token back as input, continuing until a stopping condition is met.
Q4: Can LLMs be fine-tuned?
Yes. Developers can fine-tune pretrained LLMs on specific datasets to specialize them for tasks like legal document analysis, customer support, or financial forecasting. Learn more in Fine-Tuning LLMs 101
Q5: What are the limitations of how LLMs work?
LLMs may hallucinate facts, lack true reasoning, and can be sensitive to prompt structure. Their outputs reflect patterns in training data, not grounded understanding. Learn more in Cracks in the Facade: Flaws of LLMs in Human-Computer Interactions
Conclusion: Why You Should Understand How LLMs Work
Understanding how LLMs work helps you unlock their full potential, from building smarter AI systems to designing better prompts. Each stage—tokenization, embedding, attention, inference, and output generation—plays a unique role in shaping the model’s behavior.
Whether you’re just getting started with AI or deploying LLMs in production, knowing how LLMs work equips you to innovate responsibly and effectively.
Ready to dive deeper?