Great question! The decimal in AI product versioning (like GPT-4.0, Claude 2.1, etc.) usually comes from semantic versioning, which is a common way to track software updates. Here's what it generally means:

Major version (before the decimal): Big changes, overhauls, or milestones (e.g., GPT-4 vs GPT-3).

Minor version (after the decimal): Smaller improvements, tweaks, or new features (e.g., GPT-4.1 might be faster or more accurate than 4.0).

Sometimes a third number is used (like 4.1.2), which refers to bug fixes or patches.

It’s not just AI—this is standard in software dev. But in AI, where models evolve quickly, versioning helps people understand how much a model has changed and whether it’s still the same core architecture or a new generation.