The deal, which keeps Austin with the Rams through 2021, includes $30 million guaranteed, with incentives that could elevate the deal's value to $52 million, the source told Schefter.
Austin significantly increased his production in 2015, setting career highs in receptions (52), yards from scrimmage (907) and touchdowns (10), prompting the Rams to trigger his fifth-year option for 2017.
Austin, the eighth overall selection in the 2013 draft, carries a base salary of $2,143,773 in 2016 and is set to make $12,268,000 in 2017.
His role is expected to increase this season -- in the passing game and out of the backfield -- under Rob Boras and new passing game coordinator Mike Groh. Austin will also continue to return punts.