The 6 Major Types of LLMs You Need to Know

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Large Language Models (LLMs) are transforming AI, but not all are built the same. Here’s a breakdown of the six major types:

1. Autoregressive LLMs

  • Generate text sequentially by predicting the next word based on previous tokens.
  • Example: GPT-3, GPT-4.

2. Autoencoder LLMs

  • Use deep bidirectional context to reconstruct masked tokens.
  • Example: BERT, RoBERTa.

3. Seq2Seq LLMs (Encoder-Decoder)

  • Convert input sequences into structured outputs (e.g., translation, summarization).
  • Example: T5, BART.

4. Multimodal LLMs

  • Process text, images, audio, and video for cross-format understanding.
  • Example: OpenAI’s CLIP, Google’s Gemini.

5. Instruction-Tuned LLMs

  • Fine-tuned to follow user prompts precisely.
  • Example: ChatGPT, Claude.

6. Domain-Specific LLMs

  • Specialized in fields like law, medicine, or finance.
  • Example: BloombergGPT (finance), Med-PaLM (healthcare).

You Should Know:

How to Work with Different LLMs

1. Autoregressive LLMs (GPT-like Models)

from transformers import GPT2LMHeadModel, GPT2Tokenizer

tokenizer = GPT2Tokenizer.from_pretrained("gpt2") 
model = GPT2LMHeadModel.from_pretrained("gpt2")

input_text = "The future of AI is" 
inputs = tokenizer(input_text, return_tensors="pt") 
outputs = model.generate(inputs, max_length=50)

print(tokenizer.decode(outputs[bash], skip_special_tokens=True)) 

2. Autoencoder LLMs (BERT-like Models)

from transformers import BertTokenizer, BertForMaskedLM

tokenizer = BertTokenizer.from_pretrained("bert-base-uncased") 
model = BertForMaskedLM.from_pretrained("bert-base-uncased")

input_text = "The [bash] of AI is revolutionary." 
inputs = tokenizer(input_text, return_tensors="pt") 
outputs = model(inputs)

predicted_token = tokenizer.convert_ids_to_tokens(torch.argmax(outputs.logits[0, 5]).item()) 
print(input_text.replace("[bash]", predicted_token)) 

3. Seq2Seq LLMs (T5, BART)

from transformers import T5Tokenizer, T5ForConditionalGeneration

tokenizer = T5Tokenizer.from_pretrained("t5-small") 
model = T5ForConditionalGeneration.from_pretrained("t5-small")

input_text = "translate English to French: Hello, how are you?" 
inputs = tokenizer(input_text, return_tensors="pt") 
outputs = model.generate(inputs)

print(tokenizer.decode(outputs[bash], skip_special_tokens=True)) 

4. Multimodal LLMs (CLIP, Gemini)

import torch 
from PIL import Image 
from transformers import CLIPProcessor, CLIPModel

model = CLIPModel.from_pretrained("openai/clip-vit-base-patch32") 
processor = CLIPProcessor.from_pretrained("openai/clip-vit-base-patch32")

image = Image.open("image.jpg") 
text = ["a photo of a cat", "a photo of a dog"]

inputs = processor(text=text, images=image, return_tensors="pt", padding=True) 
outputs = model(inputs)

logits_per_image = outputs.logits_per_image 
probs = logits_per_image.softmax(dim=1).tolist()[bash]

print(f"Cat: {probs[bash]100:.2f}%, Dog: {probs[bash]100:.2f}%") 

5. Instruction-Tuned LLMs (ChatGPT, Claude)

curl https://api.openai.com/v1/chat/completions \ 
-H "Content-Type: application/json" \ 
-H "Authorization: Bearer YOUR_API_KEY" \ 
-d '{ 
"model": "gpt-4", 
"messages": [{"role": "user", "content": "Explain quantum computing."}] 
}' 

6. Domain-Specific LLMs (Fine-Tuning)

from transformers import AutoModelForCausalLM, AutoTokenizer

tokenizer = AutoTokenizer.from_pretrained("microsoft/BioGPT-Large") 
model = AutoModelForCausalLM.from_pretrained("microsoft/BioGPT-Large")

input_text = "The symptoms of diabetes include" 
inputs = tokenizer(input_text, return_tensors="pt") 
outputs = model.generate(inputs, max_length=100)

print(tokenizer.decode(outputs[bash], skip_special_tokens=True)) 

Linux & Windows Commands for AI Workflows

Linux (GPU Acceleration)

nvidia-smi  Check GPU usage 
pip install transformers torch --upgrade 
python3 -m venv llm-env && source llm-env/bin/activate 

Windows (WSL for AI Development)

wsl --install -d Ubuntu 
pip install transformers accelerate bitsandbytes 

What Undercode Say

LLMs are evolving rapidly, and choosing the right one depends on your use case. Autoregressive models excel in text generation, while autoencoders dominate classification. Multimodal models are the future, blending text, images, and audio. Instruction-tuned models make AI accessible, and domain-specific LLMs ensure precision.

Prediction

By 2026, multimodal and agentic LLMs will dominate enterprise AI, reducing the need for manual fine-tuning. Quantum language models may emerge, revolutionizing encryption and optimization.

Expected Output:

A structured guide on LLM types with practical code snippets and commands for implementation.

IT/Security Reporter URL:

Reported By: Greg Coquillo – Hackers Feeds
Extra Hub: Undercode MoN
Basic Verification: Pass ✅

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