diff --git a/pyproject.toml b/pyproject.toml
index 621bd24a2..a9a16e160 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -78,7 +78,7 @@ full = [
 # Development tools and testing
 dev = [
     "xarray<2026.5",  # TODO: drop once linopy ships xarray 2026.3+ compat fix
-    "tsam==3.3.0",  # Time series aggregation for clustering
+    "tsam==3.4.0",  # Time series aggregation for clustering
     "pytest==9.0.3",
     "pytest-xdist==3.8.0",
     "nbformat==5.10.4",