On the 18 April 2017 the Federal government made a surprise announcement to abolish the 457 temporary work (skilled) visa. It will be replaced with a new Temporary Skills Shortage (TSS) visa. The new TSS visa will have 2 streams, the short term stream that expires after 2 years, and the medium term TSS that will expire after 4 years. The eligibility criteria has been significantly tightened and the list of medium terms jobs restricted. The changes to the visas will be completed by March 2018. Current 457 visas will remain in effect.
Read the Department of Immigration and Border Protection page.