diff --git a/flixopt/transform_accessor.py b/flixopt/transform_accessor.py
index 30fc12a9d..579d4597b 100644
--- a/flixopt/transform_accessor.py
+++ b/flixopt/transform_accessor.py
@@ -88,7 +88,7 @@ def build_cluster_weights(self) -> xr.DataArray:
         Returns:
             DataArray with dims [cluster, period?, scenario?].
         """
-        return self._unrename(self._agg_result.cluster_weights.rename('cluster_weight'))
+        return self._unrename(self._agg_result.cluster_counts.rename('cluster_weight'))
 
     def build_typical_periods(self) -> dict[str, xr.DataArray]:
         """Build typical periods DataArrays with (cluster, time, ...) shape.
diff --git a/pyproject.toml b/pyproject.toml
index b7bddbfad..347f9b253 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -70,7 +70,7 @@ tutorials = [
 
 # Full feature set (everything except dev tools)
 full = [
-    "tsam_xarray >= 0.6.1, < 1",  # Time series aggregation for clustering (wraps tsam); 0.6.1 adds aggregate(cluster_on=)
+    "tsam_xarray >= 0.6.5, < 1",  # Time series aggregation for clustering (wraps tsam); 0.6.5 renames cluster_weights to cluster_counts
     "tsam >= 3.4.0, < 4",  # Directly imported for ClusterConfig, ExtremeConfig, SegmentConfig
     "pyvis==0.3.2",  # Visualizing FlowSystem Network
     "scipy >= 1.15.1, < 2", # Used by tsam. Prior versions have conflict with highspy. See https://github.com/scipy/scipy/issues/22257
@@ -87,7 +87,7 @@ full = [
 # Development tools and testing
 dev = [
     "xarray<2026.8",  # TODO: drop once linopy ships xarray 2026.3+ compat fix
-    "tsam_xarray==0.6.1",  # Time series aggregation for clustering (wraps tsam)
+    "tsam_xarray==0.6.5",  # Time series aggregation for clustering (wraps tsam)
     "tsam==3.4.0",  # Directly imported for ClusterConfig, ExtremeConfig, SegmentConfig
     "pytest==9.1.1",
     "pytest-xdist==3.8.0",