Chapter 6: AI ChatGPT-3.5
What is Generative AI – ChatGPT-3.5 (or more precisely, ChatGPT powered by GPT-3.5 / GPT-3.5 Turbo).
I’m going to explain it like a real teacher would in February 2026: slowly, with history, how it works, why it felt magical at the time, real examples (including ones you can still try today), comparisons to newer models, and the honest truth about where it stands right now.
1. Quick Big-Picture: Where does ChatGPT-3.5 fit in Generative AI?
Generative AI = AI that creates new content (text, images, code, music, etc.) from a prompt.
ChatGPT = OpenAI’s famous conversational chatbot product (launched Nov 30, 2022).
ChatGPT-3.5 (what most people called it in 2022–2024) = the free version of ChatGPT that ran on the GPT-3.5 family of models — specifically the optimized GPT-3.5 Turbo variant after early 2023.
It was the first massively popular generative AI chatbot that felt like talking to a super-smart friend who knew almost everything.
2. Historical Timeline – Why it exploded (blackboard style)
- June 2020 — OpenAI releases GPT-3 (175 billion parameters, API only, very expensive)
- Nov 2022 — OpenAI launches ChatGPT (free research preview) powered by GPT-3.5 series (fine-tuned with RLHF = Reinforcement Learning from Human Feedback) → Reached 1 million users in 5 days, 100 million in 2 months — fastest-growing consumer app ever
- Jan–March 2023 → GPT-3.5 Turbo released: faster, cheaper, better at following instructions, 4k → 16k context later
- 2023–2024 → Became the default free model in ChatGPT
- Mid-2024 onward → Gradually upgraded under the hood (better speed, fewer errors), but still called “GPT-3.5 Turbo”
- 2025–Feb 2026 → OpenAI shifts free tier to newer/smaller models (like GPT-4o mini successors or GPT-5.2 limited access), but legacy GPT-3.5 Turbo still exists in API and fallback modes
In Feb 2026:
- Free ChatGPT no longer defaults to pure GPT-3.5 Turbo (it’s smarter now — often GPT-5.2 mini or similar with caps)
- But the “GPT-3.5” label is still remembered as the “classic free ChatGPT” that introduced billions to GenAI
3. Technical breakdown – What made ChatGPT-3.5 special? (no heavy math)
- Base: Decoder-only transformer (same architecture family as all modern LLMs)
- Training: Pre-trained on huge internet text (up to ~2021 cutoff originally), then fine-tuned with RLHF so it behaves helpfully, safe, and chatty
- Context window: 4,096 tokens initially → 16,385 tokens in later Turbo versions (≈ 12,000–13,000 words)
- Strengths in 2022–2024:
- Very fast responses
- Cheap to run (hence free tier possible)
- Good at creative writing, code, translation, brainstorming, explaining concepts
- Followed instructions much better than raw GPT-3
- Weaknesses (very obvious by 2026 standards):
- Hallucinates facts more often
- Weak reasoning on hard math/logic/multi-step problems
- Short context compared to 128k–256k+ in 2026 models
- No native vision/voice (added later in GPT-4o era)
4. Real examples – What ChatGPT-3.5 could (and still can) do well
You can still test similar behavior today (free ChatGPT fallback or API with gpt-3.5-turbo).
Example 1 – Creative fun (one of the first viral uses) Prompt (2022 style): “Write a funny conversation between a cat and a dog arguing about who is the better pet.”
Typical 3.5 output (short, witty, charming): Cat: “Humans worship me. I get gourmet treats and naps on demand.” Dog: “They take ME on adventures! Car rides, parks, belly rubs!” Cat: “Adventures? You mean getting yelled at for chewing shoes?” Dog: “At least I don’t knock glasses off tables at 3 a.m.!” Cat: “That’s quality control, peasant.”
Example 2 – Coding help (huge for students/devs) Prompt: “Write a Python function to check if a number is prime. Add comments and handle edge cases.”
Output was usually clean & correct:
|
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 |
def is_prime(n): """Check if a number is prime.""" if n <= 1: return False if n <= 3: return True if n % 2 == 0 or n % 3 == 0: return False i = 5 while i * i <= n: if n % i == 0 or n % (i + 2) == 0: return False i += 6 return True |
Example 3 – Explaining concepts (ELI5 style) Prompt: “Explain blockchain like I’m 10 years old.”
Classic 3.5 answer (simple, analogy-heavy): “Imagine a magic notebook where everyone in the village writes down who gives candy to whom. Once something is written, nobody can erase or change it secretly — because everyone has an identical copy! That’s blockchain: a super-secure shared record book for things like money or votes.”
5. Comparison table – ChatGPT-3.5 vs modern 2026 free tier
| Feature | ChatGPT-3.5 (2022–2024 peak) | Free ChatGPT in Feb 2026 (typical) |
|---|---|---|
| Model family | GPT-3.5 Turbo | GPT-5.2 mini / similar small frontier model |
| Speed | Very fast | Even faster |
| Intelligence / Reasoning | Good for simple–medium tasks | Much stronger (better logic, fewer hallucinations) |
| Context length | 4k–16k tokens | 128k+ tokens |
| Multimodal (image/voice) | Text only | Yes (vision, voice in many cases) |
| Hallucination rate | Medium–high | Lower |
| Cost to OpenAI (free user) | Low | Still low (efficient small models) |
| Best at | Quick chat, writing, code snippets | Everything 3.5 did + hard reasoning, long docs |
6. Honest 2026 verdict from your teacher
ChatGPT-3.5 was the spark that lit the Generative AI revolution. It showed normal people (not just coders) that you could just type English and get useful, fun, creative output. Millions learned prompting, started side projects, wrote essays, debugged code, and changed careers because of it.
In February 2026:
- It’s legacy / nostalgic — like using Windows XP in an era of AI agents
- Still useful for very fast, lightweight tasks via API
- But for everyday use, even the free ChatGPT is noticeably smarter than classic 3.5
- Think of it as the “Model T Ford” of chat AI — revolutionary in its day, but we’ve moved to electric hypercars.
Got it? 🔥
Want to continue the series?
- Compare it to GPT-4 / GPT-4o / GPT-5 family?
- See what prompts still work best on 3.5-style models?
- Try a side-by-side test with current free ChatGPT?
- Or move to next topic (e.g. “What is GPT-4o” or “Introduction to reasoning models”)?
Your turn — ask away! 🚀
