ChatGPT & Large Language Models

What is ChatGPT?

ChatGPT is an AI chatbot made by OpenAI. You type something, and it responds with human-like text. As of 2025, ChatGPT is powered by GPT-5, OpenAI's most advanced model.

ChatGPT is built on a Large Language Model (LLM)—a type of AI that's been trained on massive amounts of text from the internet. It learned patterns in how words and sentences fit together.

ChatGPT in 2025

ChatGPT has evolved significantly:

• GPT-5 powered — Launched August 2025, unified model with memory and reasoning
• Massive context — Can process up to 1 million tokens (entire books)
• Multimodal — Handles text, images, audio, video, and documents
• Agentic — Can perform multi-step tasks autonomously
• Fewer hallucinations — Significant improvement in accuracy

Key Concepts

Tokens

LLMs don't read words—they read "tokens," which are chunks of text. A word might be one token or several. "ChatGPT" is two tokens: "Chat" and "GPT." This matters because:

• GPT-5 supports up to 1 million token input (100K output)
• You're often charged per token when using AI APIs

Training vs. Using

Training is when the model learns from data—this happened before you ever used it. OpenAI trained GPT-5 on massive datasets with enhanced reasoning training.

Inference is when you actually use it—the model applies what it learned to answer your questions. GPT-5 also has memory, so it can remember context from previous conversations.

Hallucinations

Sometimes AI confidently generates false information. This is called a "hallucination." While GPT-5 significantly reduced hallucinations through advanced techniques, you should still verify important facts.

Other LLMs (2025)

ChatGPT isn't the only LLM. Major competitors include:

• Claude 4 (Anthropic) — Opus 4.5 matches human engineers, strong safety focus
• Gemini 3 (Google) — Ambient, agentic AI across Google products
• Llama 3 (Meta) — Open source, can run locally
• Mistral — European open-source alternative

Tips for Better Prompts

How you ask affects what you get:

1. Be specific — "Write a 200-word email to my boss asking for Friday off" beats "write an email"
2. Give context — "I'm a beginner in Python" helps the AI calibrate its response
3. Ask for format — "Give me a bullet list" or "Explain like I'm 10"
4. Use memory — Reference past conversations for continuity
5. Iterate — Say "make it shorter" or "add more examples" to refine

What LLMs Are Good At (2025)

• Writing and editing text
• Coding and debugging (professional-level with GPT-5)
• Multi-step reasoning and planning
• Analyzing documents and data
• Translating languages
• Autonomous task completion (agentic AI)

Limitations

• Still can make errors on complex calculations
• May not have real-time information (without web search)
• Can't truly verify its own accuracy