Where?
REST API returns this format for its Event content types.
"created": "1995-07-31T13:45:00+00:00",
It has not yet been decided or discussed how to display that to the end user, other than include a timezone. I imagine that a localized datetime with timezone would be preferred, and Python has great support for formatting dates. A preferred format could be configured in the Date and Time Settings control panel with an arbitrary format code.