Generative artificial intelligence (GAI) chatbots built for mental health could deliver safe, personalized, and scalable mental health support. We evaluate a foundation model designed for mental health. Adults completed mental health measures while engaging with the chatbot between May 15, 2025 and September 15, 2025. Users completed an opt-in consent, demographic information, mental health symptoms, social connection, and self-identified goals. Measures were repeated every two weeks up to 6 weeks, and a final follow-up at 10 weeks. Analyses included effect sizes, and growth mixture models to identify participant groups and their characteristic engagement, severity, and demographic factors. Users demonstrated significant reductions in PHQ-9 and GAD-7 that were sustained at follow-up. Significant improvements in Hope, Behavioral Activation, Social Interaction, Loneliness, and Perceived Social Support were observed throughout and maintained at 10 week follow-up. Engagement was high and predicted outcomes. Working alliance was comparable to traditional care and predicted outcomes. Automated safety guardrails functioned as designed, with 76 sessions flagged for risk and all handled according to escalation policies. This single arm naturalistic observational study provides initial evidence that a GAI foundation model for mental health can deliver accessible, engaging, effective, and safe mental health support. These results lend support to findings from early randomized designs and offer promise for future study of mental health GAI in real world settings.

翻译：专为心理健康设计的生成式人工智能（GAI）聊天机器人有望提供安全、个性化且可扩展的心理健康支持。本研究评估了一个专为心理健康设计的基础模型。成年参与者在2025年5月15日至9月15日期间使用该聊天机器人，并同步完成心理健康指标测量。用户需完成知情同意、人口统计学信息、心理健康症状、社会联结及自我设定目标的评估。相关指标每两周重复测量一次，持续6周，并于第10周进行最终随访。分析方法包括效应量计算，以及通过增长混合模型识别参与者群体及其典型的参与度、症状严重程度与人口统计学特征。结果显示，用户在PHQ-9与GAD-7量表得分上呈现显著下降，且该效果在随访中得以维持。在希望感、行为激活、社会互动、孤独感及感知社会支持等方面均观察到显著改善，这些改善贯穿研究全程并在第10周随访时保持。用户参与度较高，且能预测干预效果。工作联盟水平与传统心理护理相当，并同样具有预测作用。自动化安全护栏按设计运行，其中76次会话因风险被标记，均按升级处理政策妥善处置。这项单臂自然观察性研究提供了初步证据，表明专为心理健康设计的GAI基础模型能够提供可及、高参与度、有效且安全的心理健康支持。这些结果佐证了早期随机设计研究的发现，并为未来在真实场景中开展心理健康GAI研究提供了前景。