snow chains for travelling from Geneva to Chamonix?

Its not winter. I am guessing it is like Oregon. Slide of the road in a snow storm and get checked by the police? You get fined for not having required safety equipment. But I think it is pretty unlikely to get a snow storm in April. If the weather looks bad for that day, pick some up.

Ask the rental company. They will know.

Brad,

I doubt that chains will be required on that route in mid-April, but the car rental firm will provide them if they are. As I recall, it's an easy trip from Geneva, about one hour.

As you may be aware, each driver on the rental form will require an International Driver's Permit, which is used in conjunction with your home D.L. IDP's are easily available at any AAA office for a small fee, and are valid for one year. In lieu of that, a notarized translation of the terms of your license in French will suffice.

https://www.europcar.com/driving-abroad-in-winter-conditions

We strongly recommend you check The European Commission which has
additional information on international traffic rules concerning
winter tires.

France There is no legal requirement for the use of snow tires. You should carry snow chains when travelling in France. Road
signs across France indicate when a snow chain is compulsory.

Switzerland There is no legal requirement for the use of snow tires. You should carry snow chains when travelling in Switzerland.
Road signs across Switzerland indicate when a snow chain is
compulsory.

https://www.zuerich.com/en/visit/driving-in-switzerland

Driving during winter

Winter tires are not obligatory in Switzerland, but they are highly
recommended during the cold months. In Switzerland, it can also snow
in the spring and fall; therefore driving with winter tires is
advisable between October and April. If you travel to Alpine regions,
snow chains might also be necessary. Road signs will inform you about
snow chain obligations on certain roads.

Bottom line is you don't need anything special in April if you check the weather and road conditions, then don't drive on snow covered or icy roads. If your car's outside temperature reads lower than 2C, take care for black ice, especially driving over bridges.

Bardley, Snow chains and winter tyres are two different things.
Snow chains are only required in a few very high altititude locations, and only when the road is covered in solid snow or ice. You never use them if the road surface is uncovered, as they destroy the road surface. And you can only go slow with chains on.
Snow chains would never be used in Geneva, or on any kind of main road, or probably ever in Chamonix.

Snow tyres are tyres are made of a special formulation of rubber which grips better in cold weather and on snow and ice. These are normally on all cars in Switzerland (including hire cars) from "O bis O" (= Oktober bis Ostern = October to Easter).
Since Easter can be in March, and we are currently having a very sunny spring day (20°C), I suspect most hire cars would have switched their fleet to summer tyres.