Openness is a movement toward creating a more effective ecosystem regardless this ecosystem is different type of entity such as a government or the industry. Basically, the openness can be three levels: open data, open API, open ecosystem. From the previous research, the study had identified the movement of open data to open API in Taiwan government. This research will focus the movement from open API to open ecosystem and uses Taiwan financial industry as the case study. This study finds the success open economy is an API economy and successful API economy is the cross-domain collaboration, which the participants collaborate together to create better marketplace.