[Novotny]

You can turn off the automatic updates for games. It does tell you when it's downloading, but doesn't announce it will begin to, as you've left the option for automatic updates checked. Thus, it happens automatically. If you want to do it as and when you choose, turn off automatic updates.

Steam doesn't announce its own updates, this is true. Nor does it allow them to be optional. Why? Because they're very often anti-exploitation patches. Makes perfect sense to me.