Lightcap announced his departure in a message to employees, saying he plans to "start something new." He did not disclose details about his next venture but indicated that his future work would remain connected to challenges emerging as artificial intelligence becomes more capable.
He is expected to remain available to OpenAI employees for the next few weeks to support the transition.
Lightcap joined OpenAI in 2018, several years before the launch of ChatGPT turned the company into one of the most prominent businesses in the global artificial intelligence industry.
During his tenure, he held several senior leadership positions and played a role in building OpenAI's business and operational functions. He initially served as Chief Financial Officer before becoming Chief Operating Officer in 2022.
As COO, Lightcap's responsibilities included business operations and strategy as OpenAI expanded its commercial activities and partnerships alongside the development of its AI models and products.
His role changed earlier this year as OpenAI reorganised parts of its senior leadership structure. In April, Lightcap moved away from his operating chief responsibilities to lead special projects while reporting directly to CEO Sam Altman.
The special projects role included work around strategic deals and initiatives involving enterprise software and private equity partnerships.
Denise Dresser, OpenAI's Chief Revenue Officer and former Slack CEO, assumed several commercial responsibilities previously handled by Lightcap, while company president Greg Brockman took on a larger role in product leadership.
OpenAI did not immediately appoint another COO following Lightcap's transition.
In his departure message, Lightcap reflected on the company's expansion during his tenure. He said he had helped build early versions of several organisational functions, including finance, legal, human resources, corporate security, go-to-market operations and partnerships.
The eight-year period also covered OpenAI's transition from a comparatively small artificial intelligence research organisation into a global technology company with consumer and enterprise products.
ChatGPT, launched publicly in late 2022, became the company's best-known product and accelerated commercial adoption of generative AI. OpenAI has subsequently expanded into areas including enterprise AI, coding, image and video generation, voice technology and AI agents.
Lightcap's departure comes during a broader period of leadership changes at the company. OpenAI has reshuffled responsibilities across its product, commercial and operational teams over the past year as it continues to scale its business and technology operations.
His exit also comes as competition among major AI companies intensifies across consumer assistants, enterprise software, coding tools and increasingly autonomous AI systems.
Lightcap did not specify when he would formally begin his next venture or disclose whether it would operate directly within the artificial intelligence sector.
In his message, however, he indicated that he intends to continue supporting OpenAI's mission from outside the company and suggested his next chapter would address issues connected with the increasing capabilities of AI.
His departure closes an eight-year tenure that spanned several stages of OpenAI's development, from its earlier research-focused years through the rapid commercial expansion that followed the arrival of ChatGPT.