Lexus reinforced the IS front end as part of last year’s refresh, but was unable to score higher than Acceptable in the small-overlap front test. A second revision in June 2017 has improved the score to Good, leading to the IIHS top safety honors. See for yourself, here’s video of the crash test:
The IS also received a Superior rating for its collision avoidance systems, which includes both forward collision warning and automatic emergency braking. The Lexus Safety System + is standard on all IS models.