Actuaries that use Stan?

You just need to search. Here’s a link to an actuarial case study in our set of case studies by Mick Cooney:

Case study on Loss Curves (Actuarial Science)

There was a talk at StanCon in Oxford in 2024 about insurance:

Conor Goold
Joint estimation of body and tail loss development factors in insurance: a case study using hidden Markov models in Stan

Here’s a link to their company’s Bayesian product:

Ledger Data Science Team releases BayesBlend - Ledger Newsroom

Here’s a link to an actuarial blog talking about Bayes in general and Stan in particular:

The Bayesian revolution | The Actuary

There was a whole workshop:

Stan In Insurance Workshop | Bayes Business School

The second edition of this free textbook uses Stan, STOCHASTIC LOSS RESERVING USING BAYESIAN MCMC MODELS:

https://www.casact.org/sites/default/files/2021-02/08-Meyers.pdf

That was just from the first page of Google hits for Query [stan bayesian insurance actuarial].

Peer review is a very noisy process. I got stuff through peer review before I really understood what I was doing properly and I get stuff rejected now where I’m convinced I know more than the reviewers.

No, but you have a lot of code and documentation that’s gone through peer review!