Generative Artificial Intelligence (AI) technologies have emerged as a transformative force in the content creator economy. This paper examines how platform stances toward Generative AI shape creator behavior on output-centric visual arts platforms. Two independent natural experiments are conducted on leading Chinese platforms: Lofter’s launch of an AI image generator (signaling a pro-AI stance) and Graffiti Kingdom’s prohibition of AI-generated artwork (signaling an anti-AI stance). The analysis shows that creators reduced their activity on Lofter following the AI generator launch, while activity increased, at least in the short term, on Graffiti Kingdom after the AI prohibition. Heterogeneity analysis reveals that higher-productivity, higher-popularity, multi-homing, and AI-averse creators show larger reductions in activity on Lofter. Through analysis of creator posts, three primary concerns are identified as driving resistance: replacement risk, perceived low quality, and copyright infringement.