This weekend, southbound light rail trains will not stop at Tamien station due to the platform retrofit project, which all platforms will be rebuilt at light rail stations along the Santa Teresa and Almaden lines south of Convention Center. VTA advises southbound passengers to change to a bus bridge at Convention Center to Tamien and from Tamien to Curtner. Another alternative is to get off the southbound light rail at Curtner station and transfer to a northbound train to Tamien. Partial weekend closure like this is expected sometime during the next few months at this station.
Tamien and Santa Teresa are the only stations that will not be completely closed for the construction. From late February until early next year, a group of stations will be closed for a few weeks at a time. A bus bridge will provide temporary service to the closed stations.
Once the construction completes at all stations, the light rail system will have level boarding at all doors at all stations. Currently a wooden ramp is required to board wheelchair passengers at stations without the retrofit.
Again, VTA has done a mediocre job to communicate construction impacts to passengers. There's no direct link from VTA's home page to the page about the platform retrofit. The project page, which contains the links to the construction information in PDF, is cluttered with a lot of outdated materials. The rest of the information concerning the construction is available in February's VTA Take One newsletter, also in PDF.