And to add to all other answers a little more in depth info on how it actually calculates the climbs:
This manual is for the Edge but some time ago I've read it somewhere as an official answer for 945 also.
For the Climb pro function you must always pre-load the route, and he will give you a real-time estimate of the difference in altitude and the remaining time. In case you want to use this function, I recommend the Koomot app, fantastic for creating routes and uploading them to Garmin. If you want a similar function but without loading the maps every time, use the Auto-climb function and 3d speed; with the first one it will detect an automatic when you are going up a hill and it will show you the screen with vertical speed. With the second one you will estimate the step based on the difference in altitude covered. Excellent both. ;)
What qualifies as a climb in hike vs bike mode? If I preview a specific course in a bike activity, I can preview 11 climbs, if I preview the same course in a hike activity, I can preview 32 climbs. So, there is obviously different climb criteria for different activities.