Stephenson (elbow) began a rehab assignment with Single-A Inland Empire on Tuesday, allowing one run over one inning.
It was Stephenson's first game appearance in more than a year, as he's nearly completed the long road back from UCL reconstruction with an internal brace. Given the long layoff, Stephenson will likely require most, if not all, of his allotted 30 rehab days before joining the Angels' bullpen.