Chapter 7: AI ChatGPT-4

Generative AI – ChatGPT-4 (what people usually mean by “ChatGPT-4” or “GPT-4 in ChatGPT”).

By February 21, 2026, the story has evolved a lot — so I’ll explain it honestly like your real teacher would: history, what it actually was, key upgrades over 3.5, real examples, comparisons to today’s reality, and where “ChatGPT-4” stands right now.

1. Quick Orientation: What “ChatGPT-4” Really Refers To

• ChatGPT = the product / app / website you use (chat.openai.com)
• GPT-4 = the family of large language models OpenAI released starting March 14, 2023
• ChatGPT-4 (or “ChatGPT using GPT-4”) = when ChatGPT switched to GPT-4 family models for paid users (Plus, Team, Enterprise)

It launched as a paid upgrade ($20/month for ChatGPT Plus) — the free tier stayed on GPT-3.5 Turbo for a long time.

The GPT-4 family evolved quickly:

• Original GPT-4 (March 2023) → text + basic image input
• GPT-4 Turbo (Nov 2023) → faster, cheaper, 128k context window
• GPT-4o (“omni” — May 2024) → full multimodal (text + real-time voice + vision), faster & cheaper than Turbo
• Later variants: GPT-4.1 family, GPT-4.5 previews, etc. (2025)

But in everyday language from 2023–2025, people just said “ChatGPT-4” to mean the smarter paid version (vs free “ChatGPT-3.5”).

2. Timeline & Evolution (blackboard style – 2023 to Feb 2026)

• March 14, 2023 — OpenAI announces GPT-4 → ChatGPT Plus gets it first
• 2023–early 2024 — GPT-4 becomes the flagship for paid users; huge leap in reasoning, accuracy, coding, long answers
• Nov 2023 — GPT-4 Turbo: 128k tokens (~100 pages of text), much faster/cheaper
• May 13, 2024 — GPT-4o launch: native multimodal (text, voice, images in one model), real-time voice chat feels human-like, 2× faster, 50% cheaper than Turbo
• 2025 — GPT-4o dominates paid tier; later GPT-4.1 / mini variants for specialized tasks
• Aug 2025 — GPT-5 arrives → GPT-4o temporarily removed from ChatGPT (user backlash → brought back for paid)
• Feb 13, 2026 — OpenAI officially retires GPT-4o (and older 4.x variants) from ChatGPT interface → Free/paid users now default to GPT-5.2 family (Instant for speed, Thinking/Pro for deep reasoning) → Some voice modes still use GPT-4o mini remnants temporarily

So in February 21, 2026: “ChatGPT-4” is legacy / nostalgic. It’s no longer selectable in the main interface — the models powering ChatGPT today are smarter, longer-context, better-reasoning successors.

But understanding GPT-4 era is crucial — it was the bridge from “fun toy” (3.5) to “serious productivity tool” (2026 models).

3. What Made GPT-4 / ChatGPT-4 Feel Revolutionary? (2023–2025 perspective)

Compared to GPT-3.5:

It passed bar exam in top 10%, biology olympiad near-perfect, could “see” images and reason about them.

4. Real Examples – Classic ChatGPT-4 Strengths (you can imagine or test similar in legacy mode)

Example 1 – Complex Reasoning / Multi-step Problem Prompt: “A bat and ball cost $1.10 total. The bat costs $1 more than the ball. How much does the ball cost?”

GPT-3.5 often said: “5 cents” (intuitive but wrong). GPT-4 / 4o usually: “Let’s think step by step. Let ball = x. Bat = x + 1.00. x + (x + 1.00) = 1.10 → 2x + 1.00 = 1.10 → 2x = 0.10 → x = 0.05? Wait — but bat would be 1.05, total 1.10. Wait, bat is $1 more than ball: 1.05 is $1 more than 0.05 — yes. Correct answer: ball = $0.05, bat = $1.05.”

(Shows chain-of-thought improvement.)

Example 2 – Image + Text Multimodal (GPT-4o era) Upload photo of messy desk with handwritten note: “Meeting 3pm – bring revenue report & laptop charger”. Prompt: “What’s in this image and what action should I take?”

GPT-4o: “This is your desk with scattered papers, a coffee mug, phone, and a sticky note saying ‘Meeting 3pm – bring revenue report & laptop charger’. Reminder: grab the quarterly revenue PDF from your drive and your spare charger before heading out. Current time looks like 2:15 — you have ~45 min.”

Example 3 – Advanced Coding Prompt: “Write a React component for a real-time stock ticker using WebSocket, with error handling and loading state. Use TypeScript.”

GPT-4 / 4o produced clean, production-ready code with interfaces, hooks, fallbacks — far better than 3.5’s simpler versions.

5. 2026 Honest Teacher Verdict

ChatGPT-4 / GPT-4 family was the massive upgrade that made GenAI feel professional-grade:

• From “clever chatbot” → “virtual expert collaborator”
• Enabled real work: legal analysis, medical reasoning (with disclaimers), complex coding, creative multimodal tasks
• Sparked enterprise adoption (Microsoft Copilot, custom GPTs, API integrations)

In Feb 2026:

• It’s retired from main ChatGPT (Feb 13, 2026 announcement)
• Most users now get GPT-5.2 (faster, deeper reasoning, 256k+ context in “Thinking” mode)
• Legacy love: Some users miss GPT-4o’s “personality” / creative nuance — caused backlash when retired
• Still accessible via older API snapshots (for devs), but not recommended for new projects

Think of it as the “iPhone 4 to iPhone 6” era of AI — groundbreaking then, but we’ve moved to foldables and AI agents now.

Got the picture? 🎯

Next in the series — want to cover:

• ChatGPT-4o specifically (the multimodal star before retirement)?
• GPT-5 / GPT-5.2 (what’s powering ChatGPT today)?
• Compare GPT-4 era vs current 2026 models side-by-side?
• Or practice prompts that shined on GPT-4?

Your classroom — tell me! 🚀