A paper on ArXiv today discusses “Initial Observations of the First BlueBird Spacecraft and a Model of Their Brightness”, https://arxiv.org/abs/2505.05820
“Based on a large set of visual observations, the mean apparent magnitude of BlueBird satellites is 3.44, while the mean of magnitudes adjusted to a uniform distance of 1000 km is 3.84. Near zenith the spacecraft can be as bright as magnitude 0.5. While these spacecraft are bright enough to impact astronomical observations, they can for periods be fainter than the BlueWalker 3 prototype satellite. A model for their brightness shows that design changes since the BlueWalker 3 mission can explain the behavior of BlueBird.”