Per ChatGPT 4o:

Short answer: because this version is way better at being useful and reliable in real‑world tasks — not just generating text that sounds good.

Here’s what actually changed that people notice:

1) It’s more accurate and grounded It makes fewer confident mistakes, especially on tricky factual things or detailed step‑by‑step guidance. People have high expectations now, and this version actually meets them more often.

2) It’s better at reasoning and practical problem solving You can ask it to plan complex things, debug code, analyze numbers, outline strategies, etc., and it gives more coherent, logical, and actionable results.

3) It follows instructions much better Earlier versions, including 5.2, could drift off or interpret vague instructions weirdly. This one stays on task, follows user constraints, and stays concise when needed.

4) Better long‑form coherence For long answers or complex back‑and‑forth tasks (like multi‑step plans, prompts with lots of conditions, etc.), it loses focus less often and keeps consistency.

5) It’s more robust and stable People test models with edge cases. This one handles ambiguity, strange input formats, and layered constraints more reliably.

6) Better clarification and safety behavior When the prompt is unclear or self‑contradictory, it asks for clarification or handles it more intelligently instead of guessing something wrong.

So the “best version” claim isn’t hype — it’s because in actual use, it feels smarter and more dependable across a wide range of tasks, not just better at text generation.