diff --git a/flexmeasures/data/models/forecasting/pipelines/train.py b/flexmeasures/data/models/forecasting/pipelines/train.py
index eacde33137..7a086f9543 100644
--- a/flexmeasures/data/models/forecasting/pipelines/train.py
+++ b/flexmeasures/data/models/forecasting/pipelines/train.py
@@ -27,6 +27,7 @@ def __init__(
         forecast_frequency: int = 1,
         event_starts_after: datetime | None = None,
         event_ends_before: datetime | None = None,
+        save_belief_time: datetime | None = None,
         probabilistic: bool = False,
         ensure_positive: bool = False,
         missing_threshold: float = 1.0,
@@ -62,6 +63,7 @@ def __init__(
             max_forecast_horizon=max_forecast_horizon,
             event_starts_after=event_starts_after,
             event_ends_before=event_ends_before,
+            save_belief_time=save_belief_time,
             forecast_frequency=forecast_frequency,
             missing_threshold=missing_threshold,
         )
diff --git a/flexmeasures/data/models/forecasting/pipelines/train_predict.py b/flexmeasures/data/models/forecasting/pipelines/train_predict.py
index 7da3a98ffd..1d52bfd401 100644
--- a/flexmeasures/data/models/forecasting/pipelines/train_predict.py
+++ b/flexmeasures/data/models/forecasting/pipelines/train_predict.py
@@ -81,6 +81,7 @@ def run_cycle(
             // self._parameters["sensor"].event_resolution,
             event_starts_after=train_start,
             event_ends_before=train_end,
+            save_belief_time=self._parameters["save_belief_time"],
             probabilistic=self._parameters["probabilistic"],
             ensure_positive=self._config["ensure_positive"],
             missing_threshold=self._config.get("missing_threshold"),
diff --git a/flexmeasures/data/schemas/forecasting/pipeline.py b/flexmeasures/data/schemas/forecasting/pipeline.py
index 72371fc39a..80d1d8aec7 100644
--- a/flexmeasures/data/schemas/forecasting/pipeline.py
+++ b/flexmeasures/data/schemas/forecasting/pipeline.py
@@ -17,6 +17,7 @@
 
 from flexmeasures.data.schemas import SensorIdField
 from flexmeasures.data.schemas.times import (
+    AwareDateTimeField,
     AwareDateTimeOrDateField,
     DurationField,
     PlanningDurationField,
@@ -285,6 +286,18 @@ class ForecasterParametersSchema(Schema):
             },
         ),
     )
+    belief_time = AwareDateTimeField(
+        format="iso",
+        data_key="prior",
+        metadata={
+            "description": "The forecaster is only allowed to take into account sensor data that has been recorded prior to this [belief time](https://flexmeasures.readthedocs.io/latest/api/notation.html#tracking-the-recording-time-of-beliefs). "
+            "By default, the most recent sensor data is used. This field is especially useful for running simulations.",
+            "example": "2026-01-15T10:00+01:00",
+            "cli": {
+                "option": "--prior",
+            },
+        },
+    )
     max_forecast_horizon = DurationField(
         data_key="max-forecast-horizon",
         required=False,
@@ -419,7 +432,10 @@ def resolve_config(  # noqa: C901
         else:
             predict_start = data["start"]
 
-        save_belief_time = now if data.get("start") is None else predict_start
+        save_belief_time = data.get(
+            "belief_time",
+            now if data.get("start") is None else predict_start,
+        )
 
         if data.get("end") is None:
             data["end"] = predict_start + data["duration"]