I'm actually a happy IBMer (unpopular opinion here I'm sure:), and happen to have a great long term relationship with my management chain, so I inform them of everything, both in a friendly and official capacity. Makes everything easy. I even told my boss when I had a completely unrelated side business (music at parties) etc.

When it comes to open source contributions, both business conduct guidelines and open source mandatory yearly certs are unambiguous about transparency and approval of open source contributions. So it's pretty mandatory I think to inform, and limited if any impetus not to open open about it.

Working for a big corporation is a bit cyberpunky/Snowcrashy in that way I suppose.