If you have cracks on windows caulk there could be e few things. Wrong caulk, too cold/wet etc. Check the window frames to see if they are still tightly secured and the shades themselves to see if you notice any obvious gaps from things losing, out of square etc. Caulk is a last line of defense between you and the elements. It will only normally fail due to wrong type, poor installation (dirt water etc.) or too much movement for the caulk to take.

If you see those cracks you must contact your windows supplier and check the warranty. The main thing would be to pursue the warranty with the contractor while it's still covered. Keep good notes with dates, times, items discussed, promised follow ups, etc in case things get ugly later.

It's better for you to buy windows with better quality because if you use cheap windows, cheap installation, and cheap caulk you may have problems windows being drafty. If your contractor gives you a choice, use only brands that you know. Some brands will have their name etched in the corner of the glass in real small letters.

Additionally, there really shouldn't be large gaps and the right amount and correct placement of fasteners should hold it tight to the building.Basically slip in and glue windows are bad. There should be insulation in the spaces so even if there were gaps, air would have a hard time moving by. Then there should be flashing that creates both air and water baffles to prevent air and water from getting buy and rotting your framing and siding. If this was on stucco, it should have been ground down so it is a flat and parallel plane.