Halfway Through GSoC

Hey everyone! We have officially hit the halfway mark of the Google Summer of Code (GSoC) 2026 coding period.

These past two weeks have been heavily focused on expanding the Neural Network Builder API beyond just standard NPE (Neural Posterior Estimation) models. I have successfully merged PRs #1904 and #1912 into the gsoc-2026 branch for sbi.

Here is a breakdown of what I worked on, the architectural challenges we solved, and some vital lessons learned about failing fast and role-neutral design.

PR #1904: Integrating the Builder into NLE

In my previous PR, we successfully wired the DensityEstimatorBuilder into NPE trainers. The next logical step was to do the same for Neural Likelihood Estimation (NLE) trainers. However, this brought up an immediate architectural challenge regarding how the builder signs its inputs.