How much should the front wheel flex I recently changed the speedometer on my bike, and had some problems to adjust the magnet on the spokes as well as the sensor. (The spokes are flat, and the magnet that came with the sensor was intended for round spokes. And there's not much clearance between the fork and the spokes.) But in the end I managed to get it up and running with a couple of mm gap between the two.

However. When I accelerate hard or go up steep hills I notice that the magnet hits the sensor. Apparently the front wheel flexes significantly, even when I'm not standing up or pulling seriously at the handlebars. Is this normal? How much flex would one expect in the front wheel?

It's a new CF road bike and the wheels are 'FSA Team 30', decent entry-level aluminium wheels, according to most reviews.
The amount a wheel will flex will vary greatly depending on front/rear, spoke count, rim material and rider weight.

The pedalling force that drives the bike passes through the rear wheel, so it is not uncommon for carbon rear wheels to flex significantly when a stronger/heavier rider is climbing.

For an aluminium rimmed front wheel with spokes that are correctly tensioned and a rider not exceeding the weight limit for the wheel then several mm of flex are not normal.