diff --git a/CHANGELOG.md b/CHANGELOG.md
index c92c3ea6d64..e6b12e0e0f3 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -17,6 +17,7 @@ This project adheres to [Semantic Versioning](http://semver.org/).
 - Fix Plotly Express mutating lists passed to the `x` or `y` arguments in wide mode [[#5727](https://github.com/plotly/plotly.py/pull/5727)], with thanks to @cpruijsen for the contribution!
 - Fix `px.sunburst`, `px.treemap` and `px.icicle` listing sectors in a different order on every run when `path` is used with a Polars DataFrame; sectors now follow their order of first appearance for all dataframe backends [[#5766](https://github.com/plotly/plotly.py/pull/5766)], with thanks to @Irahan2 for the contribution!
 - Fix `mpl_to_plotly` conversion of matplotlib contour lines and line collections: close contour rings ending with `Z` codes, support dash styles, convert date x-axes, separate disjoint subpaths with `None` separators, hide line collection traces from the legend by default, and group consecutive same-style lines into single traces [[#5770](https://github.com/plotly/plotly.py/pull/5770)], with thanks to @robertoffmoura for the contribution!
+- Fix axis and plot titles disappearing when set with a plain string (e.g. `{"xaxis.title": "Time"}` or `{"xaxis": {"title": "Time"}}`) in the `args` of `updatemenus` buttons or `sliders` steps; such titles are now converted to `title.text` as they are elsewhere in a figure [[#5032](https://github.com/plotly/plotly.py/issues/5032)]
 
 ## [7.1.0] - 2026-09-15
 
diff --git a/_plotly_utils/basevalidators.py b/_plotly_utils/basevalidators.py
index 1ffc63e5add..ebde592d1d0 100644
--- a/_plotly_utils/basevalidators.py
+++ b/_plotly_utils/basevalidators.py
@@ -2232,6 +2232,57 @@ def present(self, v):
                 return tuple(v)
 
 
+class MethodArgsValidator(InfoArrayValidator):
+    """
+    Validator for the `args` / `args2` properties of updatemenu buttons and
+    slider steps, which hold the arguments passed to a Plotly.js method
+    (e.g. `restyle`, `relayout`, `update`) when the control is activated.
+
+    Plotly.js no longer accepts a string (or number) for a `title` attribute,
+    so, as `TitleValidator` does for figure properties, such values are mapped
+    to the `text` property of the title:
+
+      - `{"xaxis.title": "Time"}` -> `{"xaxis.title.text": "Time"}`
+      - `{"xaxis": {"title": "Time"}}` -> `{"xaxis": {"title": {"text": "Time"}}}`
+    """
+
+    def validate_coerce(self, v):
+        v = super(MethodArgsValidator, self).validate_coerce(v)
+        if v is not None:
+            v = [
+                MethodArgsValidator._coerce_title_strings(el, top_level=True)
+                for el in v
+            ]
+        return v
+
+    @staticmethod
+    def _coerce_title_strings(v, top_level=False):
+        # Only dicts (i.e. attribute/value objects) are inspected, so strings
+        # in other positions (e.g. animation frame names) are left alone.
+        # A new dict is returned so that the user's input is not mutated.
+        if not isinstance(v, dict):
+            return v
+
+        res = {}
+        for key, val in v.items():
+            if (
+                isinstance(key, str)
+                and key.split(".")[-1] == "title"
+                and isinstance(val, (str, int, float))
+            ):
+                if top_level and key + ".text" not in v:
+                    # Top-level keys are attribute paths, so only update the
+                    # title text and keep the other title properties
+                    # (e.g. font), as Plotly.js did before version 3.
+                    res[key + ".text"] = val
+                    continue
+                val = {"text": val}
+            else:
+                val = MethodArgsValidator._coerce_title_strings(val)
+            res[key] = val
+        return res
+
+
 class LiteralValidator(BaseValidator):
     """
     Validator for readonly literal values
diff --git a/codegen/utils.py b/codegen/utils.py
index e62c5533795..bd238ff0cd3 100644
--- a/codegen/utils.py
+++ b/codegen/utils.py
@@ -179,6 +179,9 @@ def format_description(desc):
     "layout.template": "_plotly_utils.basevalidators.BaseTemplateValidator",
     "frame.data": "plotly.validators.DataValidator",
     "frame.layout": "plotly.validators.LayoutValidator",
+    "layout.updatemenu.button.args": "_plotly_utils.basevalidators.MethodArgsValidator",
+    "layout.updatemenu.button.args2": "_plotly_utils.basevalidators.MethodArgsValidator",
+    "layout.slider.step.args": "_plotly_utils.basevalidators.MethodArgsValidator",
 }
 
 
diff --git a/plotly/validators/_validators.json b/plotly/validators/_validators.json
index c923bc67e6a..921abaa1199 100644
--- a/plotly/validators/_validators.json
+++ b/plotly/validators/_validators.json
@@ -4110,7 +4110,7 @@
                 }
             ]
         },
-        "superclass": "InfoArrayValidator"
+        "superclass": "MethodArgsValidator"
     },
     "layout.updatemenu.button.args": {
         "params": {
@@ -4133,7 +4133,7 @@
                 }
             ]
         },
-        "superclass": "InfoArrayValidator"
+        "superclass": "MethodArgsValidator"
     },
     "layout.updatemenu.borderwidth": {
         "params": {
@@ -8327,7 +8327,7 @@
                 }
             ]
         },
-        "superclass": "InfoArrayValidator"
+        "superclass": "MethodArgsValidator"
     },
     "layout.slider.pad": {
         "params": {
diff --git a/tests/test_core/test_graph_objs/test_method_args.py b/tests/test_core/test_graph_objs/test_method_args.py
new file mode 100644
index 00000000000..2ba1db2e030
--- /dev/null
+++ b/tests/test_core/test_graph_objs/test_method_args.py
@@ -0,0 +1,88 @@
+import json
+
+import pytest
+
+import plotly.graph_objects as go
+
+
+# Plotly.js no longer accepts strings for title attributes, so plain string
+# titles in updatemenu button and slider step args must be sent as title.text
+# (https://github.com/plotly/plotly.py/issues/5032)
+TITLE_ARGS = [
+    ({"title": "T"}, {"title.text": "T"}),
+    ({"xaxis.title": "T"}, {"xaxis.title.text": "T"}),
+    ({"yaxis2.title": "T"}, {"yaxis2.title.text": "T"}),
+    ({"scene.xaxis.title": "T"}, {"scene.xaxis.title.text": "T"}),
+    ({"coloraxis.colorbar.title": "T"}, {"coloraxis.colorbar.title.text": "T"}),
+    ({"xaxis": {"title": "T"}}, {"xaxis": {"title": {"text": "T"}}}),
+    ({"title.text": "T"}, {"title.text": "T"}),
+    ({"xaxis.title.text": "T"}, {"xaxis.title.text": "T"}),
+    ({"xaxis": {"title": {"text": "T"}}}, {"xaxis": {"title": {"text": "T"}}}),
+]
+
+
+def serialized_layout(fig):
+    return json.loads(fig.to_json())["layout"]
+
+
+@pytest.mark.parametrize("arg,expected", TITLE_ARGS)
+def test_updatemenu_button_args_title(arg, expected):
+    fig = go.Figure(
+        layout=dict(
+            updatemenus=[
+                dict(
+                    buttons=[
+                        dict(method="relayout", args=[arg], args2=[arg]),
+                        dict(method="update", args=[{"visible": [True]}, arg]),
+                    ]
+                )
+            ]
+        )
+    )
+    buttons = serialized_layout(fig)["updatemenus"][0]["buttons"]
+    assert buttons[0]["args"] == [expected]
+    assert buttons[0]["args2"] == [expected]
+    assert buttons[1]["args"] == [{"visible": [True]}, expected]
+
+
+@pytest.mark.parametrize("arg,expected", TITLE_ARGS)
+def test_slider_step_args_title(arg, expected):
+    fig = go.Figure()
+    fig.update_layout(
+        sliders=[
+            dict(
+                steps=[
+                    dict(method="relayout", args=[arg]),
+                    dict(method="update", args=[{"visible": [True]}, arg]),
+                ]
+            )
+        ]
+    )
+    steps = serialized_layout(fig)["sliders"][0]["steps"]
+    assert steps[0]["args"] == [expected]
+    assert steps[1]["args"] == [{"visible": [True]}, expected]
+
+
+def test_button_args_title_property_assignment():
+    button = go.layout.updatemenu.Button(method="relayout")
+    button.args = [{"xaxis.title": "T"}]
+    assert button.to_plotly_json()["args"] == [{"xaxis.title.text": "T"}]
+
+
+def test_restyle_args_trace_title():
+    fig = go.Figure(
+        layout=dict(
+            updatemenus=[
+                dict(
+                    buttons=[
+                        dict(
+                            method="restyle",
+                            args=[{"marker.colorbar.title": "T", "name": "N"}],
+                        )
+                    ]
+                )
+            ]
+        )
+    )
+    button = serialized_layout(fig)["updatemenus"][0]["buttons"][0]
+    assert button["args"] == [{"marker.colorbar.title.text": "T", "name": "N"}]
diff --git a/tests/test_plotly_utils/validators/test_methodargs_validator.py b/tests/test_plotly_utils/validators/test_methodargs_validator.py
new file mode 100644
index 00000000000..16a0127fb36
--- /dev/null
+++ b/tests/test_plotly_utils/validators/test_methodargs_validator.py
@@ -0,0 +1,100 @@
+import pytest
+from _plotly_utils.basevalidators import MethodArgsValidator
+
+
+# Fixtures
+
+
+@pytest.fixture()
+def validator():
+    return MethodArgsValidator(
+        "args",
+        "layout.updatemenu.button",
+        items=[{"valType": "any"}, {"valType": "any"}, {"valType": "any"}],
+        free_length=True,
+    )
+
+
+# Tests
+
+
+# Title strings are mapped to title.text
+@pytest.mark.parametrize(
+    "val,expected",
+    [
+        ({"title": "T"}, {"title.text": "T"}),
+        ({"xaxis.title": "T"}, {"xaxis.title.text": "T"}),
+        ({"yaxis2.title": 2}, {"yaxis2.title.text": 2}),
+        ({"scene.xaxis.title": "T"}, {"scene.xaxis.title.text": "T"}),
+        (
+            {"coloraxis.colorbar.title": "T"},
+            {"coloraxis.colorbar.title.text": "T"},
+        ),
+        ({"xaxis": {"title": "T"}}, {"xaxis": {"title": {"text": "T"}}}),
+        (
+            {"scene": {"xaxis": {"title": "T"}}},
+            {"scene": {"xaxis": {"title": {"text": "T"}}}},
+        ),
+        (
+            {"marker": {"colorbar": {"title": "T"}}},
+            {"marker": {"colorbar": {"title": {"text": "T"}}}},
+        ),
+    ],
+)
+def test_title_strings_coerced(val, expected, validator):
+    assert validator.validate_coerce([val]) == [expected]
+
+
+# Already valid title values are left alone
+@pytest.mark.parametrize(
+    "val",
+    [
+        {"title.text": "T"},
+        {"xaxis.title.text": "T"},
+        {"title": {"text": "T"}},
+        {"xaxis.title": {"text": "T", "font": {"color": "red"}}},
+        {"xaxis": {"title": {"text": "T"}}},
+        {"xaxis.title": None},
+        {"xaxis.title.font.color": "red"},
+    ],
+)
+def test_title_objects_unchanged(val, validator):
+    assert validator.validate_coerce([val]) == [val]
+
+
+# Strings for other properties are left alone
+@pytest.mark.parametrize(
+    "val",
+    [
+        [{"visible": [True, False]}, {"annotations[0].text": "T"}],
+        [{"name": "title"}, {"subtitle": "T", "xaxis.titlefont": "T"}],
+        [["frame1", "frame2"], {"mode": "immediate"}],
+        ["title", {"title": {"text": "T"}}],
+        [None, {"xaxis.range": [0, 1]}],
+    ],
+)
+def test_other_values_unchanged(val, validator):
+    assert validator.validate_coerce(val) == val
+
+
+def test_title_string_in_each_arg(validator):
+    assert validator.validate_coerce(
+        [{"marker.colorbar.title": "A"}, {"xaxis.title": "B"}, [0]]
+    ) == [{"marker.colorbar.title.text": "A"}, {"xaxis.title.text": "B"}, [0]]
+
+
+def test_existing_title_text_key_not_overwritten(validator):
+    val = {"xaxis.title": "A", "xaxis.title.text": "B"}
+    assert validator.validate_coerce([val]) == [
+        {"xaxis.title": {"text": "A"}, "xaxis.title.text": "B"}
+    ]
+
+
+def test_input_not_mutated(validator):
+    val = [{"xaxis.title": "A", "yaxis": {"title": "B"}}]
+    validator.validate_coerce(val)
+    assert val == [{"xaxis.title": "A", "yaxis": {"title": "B"}}]
+
+
+def test_none(validator):
+    assert validator.validate_coerce(None) is None