It currently remains unclear how readily available the testing is and so it will be a case that while some device owners are able to access the features, others won't be. Likewise, it remains unclear whether this feature will ever get beyond the testing stage and make it out to everyone.
It has been suggested the feature arrived along with the latest version of the Google app. Specifically, the updated version of the Google Beta app, and as a result it may be the case that unless a user is a Google app beta tester they are unable to access the feature regardless of anything else.
The Google Beta Android app was last updated on Friday July 19, 2019.
There does not appear to be any other particular caveats. For example, there's no suggestion the feature is linked to any particularly version of Android, including Android Q, and it is unlikely to be a feature that's solely linked to the Google Pixel line of smartphones.
For those that are seeing the new feature, it does add enough way in which the user can improve upon the Google Assistant functionality and especially when the phone is locked.
While Google Assistant does offer some functionality when a device is locked, there are a number of features that if voice prompted will result in a "you need to unlock your phone for that" response from Google Assistant. Texting is one of them.
This is primarily now what's noted as changed for some users. Instead of being prompted to unlock their phone to continue, Google Assistant will comply with the command and start the process of sending a text.
In addition, Google Assistant can complete the action in one single command. For example, instead of saying "send text" and then following up with additional commands when asked, the user can simply command Google Assistant to "send text to [enter name]" along with the actual message and Google Assistant will immediately send the text.
Once a text has been sent the user receives a confirmation the action was completed. This confirmation comes in verbal form along with a card that lets the uses visibly see that the text was sent.
One of the issues Google faces with this feature is the security as this is likely why Google requests a user to unlock a phone to continue with specific actions in the first place. They are actions related to the privacy of the user compared to a command like "what's the weather" and unlocking the phone via a PIN or fingerprint effectively authenticates the action before continuing.
This feature presumably bypasses that authentication although it is likely to be at the user's discretion. For example, enabling the option to allow "lock screen personal results" proved to be the difference during out testing for one device (Pixel 3 XL running Android Q and the latest Google beta app).
You can see an example of the feature in action below. The padlock icon at the top of the image denotes the phone is still in a locked state.