Gradient-based Planning for World Models at Longer Horizons
Source
bair.berkeley.edu
Date
Key takeaways · AI-distilled
Long-horizon planning through a world model suffers exploding/vanishing gradients because the Jacobian with respect to early actions is a product of per-step Jacobians whose conditioning scales exponentially with the planning horizon.
GRASP's key trick is stopping gradients into the state input of the world model, trusting only action gradients, because states sit on a low-dimensional manifold with adversarial-example-like brittleness in directions orthogonal to it, which the action space doesn't share.
Because the naive stop-gradient objective has a trivial minimum (stay put, then jump to the goal on the last step), GRASP adds a dense per-timestep goal term to every predicted state, balanced against the stop-gradient dynamics loss.
On the Push-T benchmarkA standard public test set for comparing AI models — the shared scoreboards behind every "model X beats model Y" claim.Full definition → at horizon 80, GRASP hit a 10.4% success rate in a median 58.9s, versus CEM's 2.8%/132.2s and LatCo's 0.0%; at horizon 40, GRASP matched CEM's roughly 60% success rate in about a quarter of the time (8.5s vs 35.3s).
GRASP periodically breaks from its fast lifted-state optimization to run a short refinement phase using the true serial rollout gradient, to keep the lifted trajectory groundingTying a model's answers to checkable sources — retrieved documents, live data, tool results — instead of letting it answer from memory alone.Full definition → in dynamics actually reachable by a real rollout.
Terms in this piece · Glossary
benchmark — A standard public test set for comparing AI models — the shared scoreboards behind every "model X beats model Y" claim.
grounding — Tying a model's answers to checkable sources — retrieved documents, live data, tool results — instead of letting it answer from memory alone.
Why it matters
It solves a specific practical bottleneck (brittle gradients through high-dimensional vision models) that has limited long-horizon planning with learned world models.