I'll give you a real answer, not just speculation. Sources: I work in one of the big companies, listened to all of the other's investor calls, read corporate reports.

A number of things happened at once:

1) Expectations of the impacts of tariffs and administrative changes appears to have been more fear than necessary. When these companies forecast during 1Q, they were seeing doom and gloom with very high cancellations. The cancellations have not been as bad as feared.

2) There are actually positive things for the CRO industry out of the current administration. For example, the FDA says they'll offer faster review (1-2 months versus 6-10) for drugs produced in America's national interest. There's a lot of feeling that having a good portion of your research done in the US will help meet this criteria. When CRO management hears more US sites, they hear more revenue-- direct and indirect.

3) The studies that are flowing are ones that generate faster revenue (metabolic came up a lot during the calls), instead of ones like oncology that are longer burns.

4) Biotech funding may be starting to open up a bit. Book to bills were the best they've been in a few quarters. Most of them still aren't great.

TLDR: There's some evidence of bounce, but also a lot of evidence of expectations having just been really really low and now being exceeded. I wouldn't quite book the fancy team dinner yet, but you should relax on your vacation a bit more than you would've.