Wow, you’re right.

Xeon vs Xenon

I had always assumed with chip names that similar it was an Intel product. How on earth didn’t they get sued?

Because simple similarity doesn’t usually result in a lawsuit? Especially if one of the words isn’t a public product name and also happens to be an existing word with no existing specific use in the industry.

Failing to defend trademarks for such similarity named and closely related products has extremely high risks.

“Xenon” is a pre-existing word. Intel’s not going to lose protection on “Xeon” for IBM using “Xenon” as an internal codename for their own CPU.

I'm guessing that they were safe in that it was more or less a 'codename' for a specific product's CPU that nobody else could buy, versus a product out on the market, left enough clear separation to avoid Trademark complaints.

The combined might of IBM and Microsoft's legal teams, even (possibly even moreso?) then, was better than Intel's to be sure.

Not even the DoJ could make Microsoft bend its knee.