We study how increases in the U.S. Social Security full retirement age (FRA) affect benefit claiming behavior and retirement behavior separately. Using long panels of Social Security administrative data, we implement complementary research designs of a traditional cohort analysis and a regression-discontinuity design. We find that while claiming ages strongly and immediately shift in response to increases in the FRA, retirement ages exhibit persistent “stickiness” at the old FRA of 65. We use several strategies to explore the likely mechanisms behind the stickiness in retirement and find suggestive evidence that employers play a role in workers' responses to the FRA.