diff --git a/py-polars/polars/expr/expr.py b/py-polars/polars/expr/expr.py
index 775a6d42372b..ec65f40af0d7 100644
--- a/py-polars/polars/expr/expr.py
+++ b/py-polars/polars/expr/expr.py
@@ -5724,21 +5724,14 @@ def xor(self, other: Any) -> Expr:
         """
         return self.__xor__(other)
 
-    def is_in(
-        self, other: Expr | Collection[Any] | Series, *, strict: bool = True
-    ) -> Expr:
+    def is_in(self, other: Expr | Collection[Any] | Series) -> Expr:
         """
         Check if elements of this expression are present in the other Series.
 
         Parameters
         ----------
         other
-            Series or sequence to test membership of.
-        strict
-            If a python collection is given, `strict`
-            will be passed to the `Series` constructor
-            and indicates how different types should be
-            handled.
+            Series or sequence of primitive type.
 
         Returns
         -------
@@ -5765,7 +5758,7 @@ def is_in(
         if isinstance(other, Collection) and not isinstance(other, str):
             if isinstance(other, (Set, FrozenSet)):
                 other = list(other)
-            other = F.lit(pl.Series(other, strict=strict))._pyexpr
+            other = F.lit(pl.Series(other))._pyexpr
         else:
             other = parse_into_expression(other)
         return self._from_pyexpr(self._pyexpr.is_in(other))
diff --git a/py-polars/polars/series/series.py b/py-polars/polars/series/series.py
index 146e3f61c601..10a4ff21a99c 100644
--- a/py-polars/polars/series/series.py
+++ b/py-polars/polars/series/series.py
@@ -3703,20 +3703,10 @@ def is_not_nan(self) -> Series:
         ]
         """
 
-    def is_in(self, other: Series | Collection[Any], *, strict: bool = True) -> Series:
+    def is_in(self, other: Series | Collection[Any]) -> Series:
         """
         Check if elements of this Series are in the other Series.
 
-        Parameters
-        ----------
-        other
-            Series or sequence to test membership of.
-        strict
-            If a python collection is given, `strict`
-            will be passed to the `Series` constructor
-            and indicates how different types should be
-            handled.
-
         Returns
         -------
         Series
diff --git a/py-polars/tests/unit/operations/test_is_first_last_distinct.py b/py-polars/tests/unit/operations/test_is_first_last_distinct.py
index bbef3208e825..00a6e0a5f259 100644
--- a/py-polars/tests/unit/operations/test_is_first_last_distinct.py
+++ b/py-polars/tests/unit/operations/test_is_first_last_distinct.py
@@ -156,8 +156,3 @@ def test_is_first_last_distinct_all_null(dtypes: PolarsDataType) -> None:
     s = pl.Series([None, None, None], dtype=dtypes)
     assert s.is_first_distinct().to_list() == [True, False, False]
     assert s.is_last_distinct().to_list() == [False, False, True]
-
-
-def test_is_in_non_strict() -> None:
-    s = pl.Series([1, 2, 3, 4])
-    assert s.is_in([2, 2.5], strict=False).to_list() == [False, True, False, False]