Quick Answer
ChatGPT is an AI chatbot developed by OpenAI, launched in November 2022. It runs on GPT-4o, a large language model trained on vast amounts of text, which gives it the ability to answer questions, write, summarise, translate, code, and reason about almost any topic. In 2026, ChatGPT is the most widely used AI assistant in the world, with over 200 million weekly active users. It is one of several large language model products; competitors include Claude (Anthropic) and Gemini (Google).
A team of people watching a glowing red neural brain structure in a dark room: ChatGPT represented the moment AI became widely visible to the public, a shared brain that teams could interact with.
ChatGPT's launch in November 2022 was the moment AI became visible to everyone: a shared, conversational intelligence that teams could interact with for the first time.

What ChatGPT can do

ChatGPT is a general-purpose conversational AI assistant. Its core capabilities:

Writing and editing

  • Draft emails, reports, proposals, articles, and presentations
  • Edit for clarity, tone, grammar, and conciseness
  • Summarise long documents or research papers
  • Translate between languages (supports 50+ languages)

Coding

  • Write code in Python, JavaScript, SQL, TypeScript, and dozens of other languages
  • Explain what a piece of code does
  • Debug errors and suggest fixes
  • Refactor code for readability or performance

Analysis and reasoning

  • Answer questions about documents you paste in
  • Compare options and recommend based on criteria you specify
  • Break down complex problems into steps
  • Draft structured plans, outlines, and checklists

Creative tasks

  • Write stories, scripts, poems, and presentations
  • Brainstorm ideas and suggest variations
  • Generate image prompts for DALL-E 3 or Midjourney

The GPT model family

ChatGPT has been built on successively more capable models since launch:

GPT-4o (current flagship)
128K context window Text, image, audio input Strongest reasoning Available in ChatGPT Plus and via API. Multimodal: reads images, describes charts, analyses documents.
GPT-4o mini (free tier)
128K context Faster and cheaper Handles most tasks well. Lower performance on complex reasoning. Used in free ChatGPT and as the default API model for high-volume use.
o3 / o4-mini (reasoning models)
Slower generation Stronger at maths and logic Designed for tasks requiring step-by-step reasoning. Used in scientific research, coding competitions, and complex analysis. More expensive.

How ChatGPT works

ChatGPT is built on GPT-4o, a transformer-based large language model. It generates responses by predicting the most likely next token given the full conversation history.

What makes it feel like a genuine assistant rather than a raw text predictor is the training pipeline:

  1. Pre-training: GPT-4o is trained on hundreds of billions of words of text from the internet, books, and code. It learns language patterns, facts, and reasoning structures from this data.

  2. Instruction fine-tuning: The model is further trained on human-written examples of question-answer pairs. It learns to follow instructions rather than just predict text.

  3. RLHF: Human raters compare multiple responses and rank them. A reward model learns what responses humans prefer. The LLM is tuned to produce higher-ranked responses.

The result is a model that feels cooperative, helpful, and able to engage with almost any topic.

ChatGPT vs Claude vs Gemini

ChatGPT (GPT-4o)Claude claude-opus-4-8Gemini 2.0 Flash
ProviderOpenAI (US)Anthropic (US)Google (US)
Context window128K tokens200K tokens1M tokens
Best forGeneral tasks, GPT pluginsLong docs, careful reasoningSpeed, large context, Google Workspace
Image inputYesYesYes
Voice modeYes (Advanced Voice)No (as of June 2026)Yes
API pricing (input/1M)~€4.50~€3.00~€0.10
EU data residencyNo (US only)No (US only)EU option available
Enterprise DPAYes (Enterprise plan)Yes (Claude for Work)Yes (Google Workspace)

What ChatGPT cannot do

Recall recent events without web search: GPT-4o’s training data has a knowledge cutoff. Without web search enabled, it does not know what happened after that date.

Give reliable specific facts: ChatGPT hallucinate. It can state statistics, URLs, names, and dates with confidence when the information is fabricated. Always verify specific factual claims from authoritative sources.

Take actions in the world without tools: The base ChatGPT chat interface only generates text. ChatGPT can browse the web (when enabled) and run code (in the code interpreter). It cannot book flights, send emails, or update databases on its own without additional integration.

Maintain memory across sessions: Each conversation starts fresh unless you enable the Memory feature (Plus tier). ChatGPT does not remember that you told it your name last week.

Guarantee accuracy for high-stakes decisions: Legal, medical, and financial decisions require human expert review. ChatGPT’s output is a starting point, not a conclusion.

You type Send a message Your message is added to the conversation history and sent to GPT-4o as the full context.
→
Model runs Token prediction GPT-4o generates one token at a time, streaming each word as it is produced. It draws on its training data, not a live knowledge lookup.
→
Optional tool Web search or code If web search or the code interpreter is enabled and triggered, the model calls the tool, reads the result, and incorporates it into the response.
→
Response You receive text The generated response appears in the conversation. You can ask follow-up questions: the model remembers everything in the current session.

Using GPT-4o via the OpenAI API

Developers access GPT-4o directly via the API to build custom products:

python
from openai import OpenAI

client = OpenAI(api_key="YOUR_OPENAI_API_KEY")

response = client.chat.completions.create(
    model="gpt-4o",
    messages=[
        {
            "role": "system",
            "content": "You are an expert on Austrian tax law. Answer questions clearly and flag where the user should consult a registered tax advisor."
        },
        {
            "role": "user",
            "content": "Can I deduct home office costs if I work remotely three days per week in Austria?"
        }
    ],
    max_tokens=500,
)

print(response.choices[0].message.content)

What’s next

Further reading