Background <p>According to phasic models of implementation, a Preparation phase designed to enhance the implementation climate should be completed prior to the Implementation phase. Yet preparatory activities and outcomes are rarely reported or assessed in implementation research. Project MIMIC (Maximizing Implementation of Motivational Incentives in Clinics) was a hybrid type 3 effectiveness-implementation trial that compared two multi-component, phasic strategies to implement contingency management (CM) in opioid treatment programs. The current secondary analysis assessed the comparative effectiveness of the two strategies on 5-month Preparation phase outcomes: attainment of knowledge and fidelity benchmarks, implementation climate at the end of the Preparation phase, and time required for providers to complete the final preparatory/pre-implementation activity of enrolling and scheduling their first CM patient.</p> Methods <p>Twenty-eight opioid treatment programs and 186 staff were cluster-randomized to receive the Addition Technology Transfer Center (ATTC) control strategy (didactic&#xa0;workshop + performance feedback + consultation) or the theory-driven Enhanced-ATTC (E-ATTC) experimental strategy. During the Preparation phase, the E-ATTC strategy consisted of the ATTC strategy plus monthly Implementation Sustainment Facilitation sessions rooted in principles of team-based motivational interviewing to cultivate a strong implementation climate and accelerate successful completion of the Preparation phase.</p> Results <p>Across the 28 OTPs and 186 staff, attainment of knowledge and fidelity benchmarks favored the E-ATTC but did not differ significantly by condition. Implementation climate ratings after the Preparation phase were high in both conditions with no conditional differences. Providers randomized to E-ATTC completed their final preparatory activity at significantly higher rates than those randomized to ATTC. Cox regression revealed that receipt of the E-ATTC strategy was also associated with significantly faster completion of the final Preparation activity.</p> Conclusions <p>Consistent with hypotheses, the theory-driven implementation strategy was associated with higher levels of and faster time to completion of preparatory activities, a key indicator of readiness for implementation.&#xa0;Counter to expectations, this was not driven by differences in implementation climate. High ratings of implementation climate at baseline limited our ability to detect change over time, highlighting a need for alternate strategies to measure putative mechanisms of change. This analysis adds to the scant literature reporting Preparation phase strategies and outcomes, which are strong predictors of successful implementation.</p> Trial registration <p>This study is registered in Clinicaltrials.gov (NCT03931174).</p>