The rapid diffusion of artificial intelligence (AI) assistants into workplace processes has sparked a contentious debate regarding whether these technologies stimulate or suppress human innovation. Grounded in self-determination theory, this study investigates the double-edged effects of AI assistants on knowledge workers’ innovative behavior. Analysis of data collected through a situational experiment involving 400 employees across seven Chinese enterprises reveals the coexistence of opposing mechanisms. Specifically, AI-assistant intelligence enhances innovative performance both directly and indirectly by reducing perceived work intensity. However, highly intelligent AI assistants simultaneously trigger personal development concerns, thereby inhibiting innovative behavior. Crucially, organizational AI readiness functions as a critical boundary condition that amplifies both the positive pathway of reduced workload and the negative pathway of development concerns. By explicating how AI assistants can concurrently bolster and undermine innovation, this study contributes to the “AI-driven innovation” debate and offers insights for maximizing the benefits of AI while mitigating its drawbacks.