Every three months the rate of interest used to benchmark Swiss rents is reviewed. If it goes down some renters have the right to request a decrease in rent. This time the reference rate fell from 1.50% to 1.25%.
The last time it dropped was 2 June 2017 when it fell to 1.5%.
The rate is based on the average Swiss mortgage rate over three months. This rate is then rounded to the nearest 0.25%. On 31 December 2019 that rate was 1.37%, which is closer to 1.25% (-0.12) than 1.5% (+0.13).
In general if your rental contract links your rent to mortgage interest rates then you can demand a decrease in rent when this reference rate declines. The Swiss Association of Tenants, Romande branch, provides useful information on when and how to go about making a demand. Their website (in French) can be found at www.asloca.ch. Similar information can be found here in German.
Whether you qualify for a reduction will depend on your rental contract. Tenancy associations advise that landlords are unlikely to automatically offer a reduction. To get one you will generally need to contact your landlord and request a reduction.
Reference rates since September 2008 can be viewed here.