I am not an expert on PROC MODEL, but I thought that gmm would require an INSTRUMENTS statement, which here would be pretty simple. If you explicitly specify the moments, then it might be an intercept only situation.
For examples, see 19.18 Duration Data Model with Unobserved Heterogeneity in the SAS/ETS13.2 documentation.
Registration is open! SAS is returning to Vegas for an AI and analytics experience like no other! Whether you're an executive, manager, end user or SAS partner, SAS Innovate is designed for everyone on your team. Register for just $495 by 12/31/2023.
If you are interested in speaking, there is still time to submit a session idea. More details are posted on the website.