How can I get spline bases from "stan_surv"?

I’m fitting a survival model with a cubic spline base hazard and two internal knobs, which results in 6 polynomial bases. I want the spline bases formula to be able to calculate hazard at any time point. If my fitted model is called mod1, I know I can get them, but only for the death times, using mod1$basehaz$basis. Is there a way go get the actual formula of the 6 bases?
I know a dirty (but probably very accurate) way of doing it is to fit a third degree polynomial to each column of mod1$basehaz$basis, but I wanted to check and see if it’s possible to access the exact bases formula.
I’m new to splines so please let me know if I was wrong about the way I framed the question, and please let me know if you need me to put any code or output.
Thank you in advance!

  • Operating System: Windows 11
  • rstanarm Version: 2.32.1