The installers for unreleased versions of Chromium Edge have leaked online. One, which is for the Stable version of Edge, doesn't function correctly, while the Beta version appears to install just fine.
Unfortunately, that beta version is based on 184.108.40.206, which is still lower than the latest dev build. However, it does mark the first time we've seen a beta version for Chromium Edge in the wild and indicates that this phase of testing is coming soon.
Users say the build fails to launch occasionally, is sluggish on some sites, and crashes frequently. As a result, you should probably stick to official releases for now, though this could be fun to play around with.
Nearing Official Release
Both installers come directly from Microsoft's servers but aren't listed on its website. They were spotted by Twitter's WalkingCat. The stable Edge version returns the error “There was a problem installing due to a server issue. Please try again later”.
It's unclear if the download was blocked post-launch, or if the early installer simply doesn't point to anything yet. For reference, Edge is supposed to reach stable by late 2019 or early 2020. Beta builds previously leaked in May.
Among other things, Chromium Edge offers increased performance over regular Edge, as well as expanded addon support. Developer versions of the browser have been relatively smooth so far, and IT professionals have even been instructed to begin testing. However, there are still a few features Microsoft is waiting on, including a dedicated IE mode, better PDF support, and offline deployment.
At the time of writing, it's still possible to download both installers from Microsoft.