Background: The learning and working environment for resident physicians shifted dramatically over the past two decades, with increased focus on work hours, resident wellness, and patient safety. Following two multi-center randomized trials comparing 16-h work limits for PGY-1 trainees to more flexible rules, the ACGME implemented new flexible work hours standards in 2017. Objective: We sought to determine program directors’ (PDs) support for the work hour changes and programmatic response. Design: In 2017, US Internal Medicine PDs were surveyed about their degree of support for extension of PGY-1 work hour limits, whether they adopted the new maximum continuous work hours permitted, and reasons for their decisions. Key Results: The response rate was 70% (266/379). Fifty-seven percent of PDs (n = 151) somewhat/strongly support the new work hour rules for PGY-1 residents, while only 25% of programs (N = 66) introduced work periods greater than 16-h on any rotation. Higher rates of adopting change were seen in PDs who strongly/somewhat supported the change (56/151 [37%], P < 0.001), had tenure of 6+ years (33/93 [35%], P = 0.005), were of non-general internal medicine subspecialty (30/80 [38%], P = 0.003), at university-based programs (35/101 [35%], P = 0.009), and with increasing number of approved positions (< 38, 10/63 [16%]; 38–58, 13/69 [19%]; 59–100, 15/64 [23%]; > 100, 28/68 [41%], P = 0.005). Areas with the greatest influence for PDs not extending work hours were the 16-h rule working well (56%) and risk to PGY1 well-being (47%). Conclusions: Although the majority of PDs support the ACGME 2017 work hours rules, only 25% of programs made immediate changes to extend hours. These data reveal that complex, often competing, forces influence PDs’ decisions to change trainee schedules.