GPT-4 vs GPT-3.5: How to Tell the Difference

Not all AI-generated text is the same. Text produced by GPT-4 reads noticeably differently from GPT-3.5 output. Understanding these differences helps you identify which model likely generated a piece of content — and how hard it will be to detect.

1. Reasoning Depth

The most significant difference between GPT-4 and GPT-3.5 is reasoning ability. GPT-4 handles complex reasoning tasks far better. GPT-3.5 tends to gloss over nuance, providing surface-level explanations. GPT-4 digs deeper, considers edge cases, and acknowledges complexity.

GPT-3.5: "Renewable energy is important for reducing carbon emissions. Solar and wind power are two common types of renewable energy."

GPT-4: "The transition to renewable energy involves trade-offs that are often overlooked. Solar requires significant land use and manufacturing emissions before it becomes carbon-negative. Wind faces intermittency challenges that require storage solutions or grid redesign. Each technology has a nuanced cost-benefit profile."

2. Vocabulary and Style

GPT-3.5 has a more limited vocabulary and relies heavily on stock phrases. GPT-4 uses more precise language and varies its sentence structure. GPT-3.5 text often feels formulaic — you can almost predict the next sentence after reading the first few.

3. Handling of Instructions

GPT-4 follows complex, multi-part instructions much more reliably. If you give both models a detailed writing prompt with specific constraints, GPT-4 will follow all the instructions. GPT-3.5 is more likely to miss details or simplify them away.

4. Factual Accuracy

Both models can produce incorrect information, but GPT-4 is significantly more accurate. GPT-3.5 is more prone to making up plausible-sounding but false statements. This means that if an AI-generated passage contains factual errors, it is more likely to be from GPT-3.5 or a similar older model.

5. Detection Difficulty

GPT-4 text is harder to detect than GPT-3.5 text. Detection tools trained on GPT-3.5 data often perform worse on GPT-4 output because the newer model produces more human-like variation in its writing. This is why detection tools must constantly update their training data.

If you suspect text is from GPT-4 specifically, try our GPT-4 Detector for a targeted analysis.

Why This Matters

Understanding which model generated a piece of text is important for context. GPT-4 content is generally more sophisticated and harder to detect. If you rely on a detection tool that was trained primarily on GPT-3.5 data, you might miss GPT-4 content. Always check what models your detection tool is trained on.