Pi (Physical Intelligence VLA)

Physical Intelligence

Structures found in this family (1)

Linear Direction

By model (2)

pi0 (PaliGemma VLA backbone, predecessor of pi0.5) · 3B

Linear Direction

pi0.5 (PaliGemma VLA backbone) · 3B

Linear Direction

Observations (3)

A value-like success direction is recoverable from frozen VLAs

Sparse logit-lens directions in VLA FFN value vectors steer robot actions

Ablating general SAE feature directions in a VLA collapses grasp success

Papers

What Frozen VLAs Already Know About Success: A Probing Study of Value-Like Structure in Foundation Robot Policies (2026), Mechanistic Interpretability for Steering Vision-Language-Action Models (2025), Sparse Autoencoders Reveal Interpretable and Steerable Features in VLA Models (2026)