Unlike other beta programs in the Play Store, there is no sign up to get the Chrome beta for Android. You can download it here and install it on your compatible devices. Like all beta software however, its not recommended to run it as your daily browser or deploy it into production as there are likely still bugs to be found and there could be performance issues.
As you would expect at the 4th beta of any release, this update is pretty much a polishing update to the build. Reviewing the Git logs for this update, there are mostly patches and other fixes in this update, another indication that it is close to being ready for the Stable channel.
All of this points to the release of Chrome 65, slated for March 6th (March 13th for Chrome OS) to be on time.
Finally, for those that are curious, you can have both the Stable channel build of Chrome for Android on your phone at the same time as you have the Beta build. They do not replace each other but rather are two stand alone builds. This gives you the chance to keep the production version as your primary but test the beta build at the same time.