Ambulatory diagnostic error is a vexing problem because events unfold across time with shifting team members. Accurate and timely diagnosis relies on keeping patients and health care professionals (HCPs) on the same page, both in and between clinic visits. Experts urge shared mental models (SMMs) of the diagnostic process (DxP), because research shows their central role for effective team communication and coordination. Yet little is known about how patients and HCPs develop and sustain SMMs, especially in the dynamic setting of the DxP. While we have many examples of diagnostic errors in Safety-I research, there are few models of “what good looks like” using a Safety-II lens. Since diagnostic excellence relies on factors and interactions beyond any single HCP, progress will require identifying specific teaming behaviors that help patients and HCPs to coproduce safety at known DxP risk points. We will close this foundational knowledge gap. We will then develop and disseminate tools to support patients, care partners, interpreters and clinicians as active contributors to the DxP through 3 partnering national organizations. In our current AHRQ grant, we learned that patients have unique insights about the DxP, including identification of “diagnostic blindspots” – events or conditions pertaining to DxP safety that HCPs or systems may not observe. These include events occurring between visits, omissions, and misalignments stemming from lack of a SMM between patients and HCPs. Interestingly, online access to visit notes (“open notes”) – now nearly universal through 2021 federal legislation – may help development of SMMs because patients can gain context on HCP perspectives and potential gaps in their understanding by reading notes. One sobering finding was that the most common contributing factor to patient-reported diagnostic error was not feeling heard. Based on these data, we designed an online tool – OurDX – to elicit patient priorities, histories, and potential concerns. We found that patients with limited English proficiency (LEP) were 5x as likely to report not feeling heard, and older patients with poorer health were more likely to identify a diagnostic blindspot. Teams that work need new approaches to share information, to listen, and to respond, especially since harnessing the unique knowledge of each member (including early identification of otherwise undetected blindspots) can increase system resilience. Our diagnostic center of excellence – Safety2gether – is based on innovative and disciplined coupling of teaming science with patient engagement to coproduce diagnostic safety, with a focus on safety-II principles and priority populations: LEP and elderly patients with chronic illness and their care partners. Safety2gether will partner with patients, train learners, define future research questions, foster collaborations, and share multistakeholder tools through 3 national organizations to both learn from, and serve as a resource for, othe...