{
  "version": 1,
  "language": "en",
  "title": "Short-prefix execution and replanning",
  "description": "Current observations connect to a short candidate prefix. Dashed future paths diverge beyond that horizon. The robot executes only a trusted short prefix. It receives new observations and replans. The fan shows conceptual uncertainty, not a calibrated confidence interval.",
  "caption": "The author recommends execution of only a trusted short rollout prefix, with new observations and replanning as model uncertainty or drift becomes important. The branching fan illustrates prediction ambiguity. It is not a calibrated confidence interval or a certified safe/unsafe classifier. Author-created explanatory diagram. Playback time is illustrative and is not measured runtime.",
  "alt": "Replanning flow: a robot executes a short trusted prefix, gets observations and changes the plan, with branches for uncertainty.",
  "sources": [
    {
      "path": "content/blog/2026-06-09_world-models-for-embodied-ai/post.md",
      "description": "Article mechanism and retained citations"
    },
    "https://web.stanford.edu/class/ee364b/lectures/mpc_slides.pdf",
    "https://arxiv.org/abs/2603.25685"
  ],
  "limitations": [
    "This playback is an example. Playback duration is not measured runtime.",
    "The forecast fan is a conceptual uncertainty diagram. It gives no probability scale or safety certification.",
    "The model imagines the same short-prefix path before the robot executes it. Animation duration does not encode the physical horizon."
  ],
  "targets": {
    "current": {
      "id": "mechanism-current",
      "kind": "node",
      "label": "Current evidence"
    },
    "prefixEnd": {
      "id": "mechanism-prefixEnd",
      "kind": "node",
      "label": "End of trusted short prefix"
    },
    "reobserve": {
      "id": "mechanism-reobserve",
      "kind": "node",
      "label": "Observation + replanning"
    },
    "prefixPath": {
      "id": "mechanism-prefixPath",
      "kind": "edge",
      "label": "select candidate prefix"
    },
    "future0": {
      "id": "mechanism-future0",
      "kind": "edge",
      "label": "illustrative future"
    },
    "future1": {
      "id": "mechanism-future1",
      "kind": "edge",
      "label": "illustrative future"
    },
    "future2": {
      "id": "mechanism-future2",
      "kind": "edge",
      "label": "illustrative future"
    },
    "future3": {
      "id": "mechanism-future3",
      "kind": "edge",
      "label": "illustrative future"
    },
    "future4": {
      "id": "mechanism-future4",
      "kind": "edge",
      "label": "illustrative future"
    },
    "physicalOutcome": {
      "id": "mechanism-physicalOutcome",
      "kind": "edge",
      "label": "do prefix"
    },
    "freshEvidence": {
      "id": "mechanism-freshEvidence",
      "kind": "edge",
      "label": "read observations"
    }
  },
  "stateLabels": {
    "stage": "Stage",
    "artifact": "Artifact"
  },
  "scenarios": [
    {
      "id": "process",
      "title": "One short-prefix replanning cycle",
      "description": "This trace separates imagined continuations from a short physical action and new observation.",
      "initial": {
        "stage": "Ready",
        "artifact": "Inputs available"
      },
      "unselected": [],
      "steps": [
        {
          "title": "Observation input",
          "description": "The system reads current observations for this plan.",
          "duration": 3000,
          "active": [
            "current"
          ],
          "paths": [],
          "state": {
            "stage": "Observation input",
            "artifact": "Current observation for this plan"
          }
        },
        {
          "title": "Candidate short prefix",
          "description": "The model imagines a candidate short prefix before robot execution.",
          "duration": 3000,
          "active": [
            "prefixEnd"
          ],
          "paths": [
            "prefixPath"
          ],
          "state": {
            "stage": "Candidate short prefix",
            "artifact": "Candidate prefix before physical execution"
          }
        },
        {
          "title": "Different continuation predictions",
          "description": "The fan shows different possible continuations. It gives no calibrated confidence interval.",
          "duration": 3000,
          "active": [],
          "paths": [
            "future0",
            "future1",
            "future2",
            "future3",
            "future4"
          ],
          "state": {
            "stage": "Different continuation predictions",
            "artifact": "Conceptual future ambiguity. No calibrated confidence"
          }
        },
        {
          "title": "Short-prefix execution",
          "description": "The robot executes only the trusted short prefix.",
          "duration": 3000,
          "active": [
            "prefixEnd"
          ],
          "paths": [
            "prefixPath"
          ],
          "state": {
            "stage": "Short-prefix execution",
            "artifact": "Execution of only the trusted short prefix"
          }
        },
        {
          "title": "New observation after motion",
          "description": "The robot receives new observations after that motion.",
          "duration": 3000,
          "active": [
            "reobserve"
          ],
          "paths": [
            "physicalOutcome"
          ],
          "state": {
            "stage": "New observation after motion",
            "artifact": "New observations, not continued open-loop trust"
          }
        },
        {
          "title": "Replanning",
          "description": "The model replans with new observations. It does not continue with open-loop trust in the previous prediction.",
          "duration": 3000,
          "active": [
            "current"
          ],
          "paths": [
            "freshEvidence"
          ],
          "state": {
            "stage": "Replanning",
            "artifact": "The next prediction starts from the new observation."
          }
        }
      ]
    }
  ]
}