All devices that are assigned a secret index are first pre-tested. If we talk about key parameters, then their manufacturer will unveil much later. Bell X-1, which overcame the sound barrier, also belongs to such devices. The device managed to achieve a record speed. In the case of the X-37B, we are talking about a prototype of a new device, which they are preparing to launch in a series.
The X-37B is a reusable unmanned ship, its first flight was successfully completed in 2010. The capabilities of the device are still kept secret. This fact makes other states nervous when assessing possible risks.