Action representations inside VLA policies
Several papers treat the action interface as the main place to improve manipulation. ActionMap replaces pointwise action prediction with voxel heatmaps for translation, rotation, and gripper state. With the rest of OpenVLA-OFT unchanged, it raises the LIBERO four-suite average from 89.1% to 97.3%, and improves real Franka trials from 7/30 to 20/30 at full data.
LARA attacks the same control bottleneck through latent actions. It trains a Latent Action Model (LAM) together with a diffusion VLA policy, aligning the LAM latent with an intermediate policy feature. In the OXE-constrained LIBERO setting, LARA full reports 88.6 average success, above OpenVLA at 76.5 and its DiT-only version at 84.4.
Spline Policy is more methodological. It replaces fixed action chunks with spline parameters that can be resampled, constrained, and passed to controllers. The available excerpt gives no success-rate table, so its evidence is about compatibility and execution structure, not measured gains.