This checkpoint contains weights for the Walrus physics foundation model, fine-tuned and used for activation steering experiments described in Physics Steering: Causal Control of Cross-Domain Concepts in a Physics Foundation Model — arXiv:2511.20798v2.

The base Walrus model is a 1.3B-parameter space–time Transformer trained on 19 physical simulation datasets. See the main Walrus repo for full details on the architecture and pretraining.

Download the checkpoint and point your config at it:

Then set load_checkpoint_path to the folder containing the downloaded coalesced.pth.