It doesn't say that an iPad Air 4 uses the 1st gen. Maybe you read that the 1st gen is used with the iPad Air 3
Apple Pencil compatibility - Apple Support
The below below which is from the apple website, clearly explains the which pencil is compatible with which iPad
Apple Pencil (2nd generation)
![](https://support.apple.com/library/content/dam/edam/applecare/images/en_US/accessories/applepencil/apple-pencil-landscape-second-gen-crop.jpg)
You can use Apple Pencil (2nd generation) with these iPad models:
- iPad Air (4th generation)
- iPad Pro 12.9-inch (3rd generation) and later
- iPad Pro 11-inch (1st generation) and later
Apple Pencil (1st generation)
![](https://support.apple.com/library/content/dam/edam/applecare/images/en_US/accessories/applepencil/apple-pencil-landscape-first-gen-crop.jpg)
You can use Apple Pencil (1st generation) with these iPad models:
- iPad (8th generation)
- iPad mini (5th generation)
- iPad (7th generation)
- iPad (6th generation)
- iPad Air (3rd generation)
- iPad Pro 12.9-inch (1st or 2nd generation)
- iPad Pro 10.5-inch
- iPad Pro 9.7-inch