Ephemeral development environments provide a solution to the challenge of securing development processes without compromising developer productivity, by automatically applying security policies and reducing attack surface areas. These environments, exemplified by platforms like Ona, are particularly vital in AI-native software engineering due to their ability to combine developer speed with stringent security measures. In contrast to traditional virtual desktop infrastructure (VDI), which can hinder productivity, cloud development environments (CDEs) shift development tasks to the cloud, offering developers a streamlined and secure workspace. Ephemerality is key to their security advantages, as these short-lived environments grant only temporary access to code and networks, minimizing potential vulnerabilities and ensuring any security breach is quickly contained. This approach reduces risks such as persistent malware and code exfiltration, making it ideal for the modern development landscape where AI agents may introduce vulnerabilities.