Anyone else notice Claude suddenly using British spelling?

I'm in the U.S. and my settings are set to "English (United States)." I noticed about two weeks ago that Claude suddenly started using mostly British spelling in both its thinking summaries and responses.

A few examples:

• Colour
• Recognise
• Enrolment
• Defence
• Analyse
• Behaviour

I asked Claude why the spelling had changed, and it said it didn't know and described it as "drift."

It doesn't really affect anything, but I'm curious whether anyone else has noticed the same thing recently?

EDIT: I'm not using a VPN.