What "time" are you referring to? The one-year mark is still a couple weeks away. In my mind, that is not enough time to give you a definitive answer on your question.
And, you seem to be talking about two different things. Bloat (referring to size), and performance. Both are highly dependent on the user.
I am going to take a guess as to what you are talking about though - I remember a few updates that made Windows XP noticeably slow down. By the time I was done with XP, I was running 3x the memory I had when it was first released, just to get relatively the same performance. Vista was similar but to a lesser degree (the service packs seemed to cause it on that OS). I haven't noticed this at all in 7 or 8.
But also consider startup programs, drivers, scheduled tasks, hard drive fragmentation, these can all lead to slower performance over time. And with Windows 10 less than a year old, I can't really tell you what it's going to "bloat" to in the future.
One last thing to consider: Microsoft is calling it that last OS. New releases are coming in through Windows Update on a somewhat regular basis. You can re-install Windows from scratch, but as soon as you do it's going to want to update to that latest version again. So never again will Windows return to the exact way it was when you first installed it.