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。本研究评估了一款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、人口统计信息、心理健康症状、社会联结及自我设定目标的评估。测量每两周重复一次直至第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，用户的PHQ-9与GAD-7评分显著降低，且改善效果在随访中得以维持。在干预全程及第10周随访时，均观察到希望感、行为激活、社会互动、孤独感及感知社会支持方面的显著提升。用户参与度较高，且能预测干预效果。工作联盟关系与传统护理相当，并具有预测效力。自动化安全防护机制按设计运行，其中76次会话被标记为风险事件，均按升级策略妥善处理。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、互动性强、有效且安全的心理健康支持。这些结果印证了早期随机设计的发现，并为未来在真实场景中开展心理健康GAI研究提供了实践依据。