Can't draw spike line across subplots with make_subplots in 4.0.0

After upgrading to plotly 4.0.0, I can't see how to create a spike line across shared axes created with make_subplots.

Previously I was using code like this:

from plotly.tools import make_subplots
from plotly.io import write_html

fig = make_subplots(rows=4, cols=1, shared_xaxes=True)
x_vals = list(range(10))
y_vals = [x**2 for x in x_vals]
fig.add_scatter(x=x_vals, y=y_vals, row=1, col=1)
fig.add_scatter(x=x_vals, y=y_vals, row=2, col=1)
fig.add_scatter(x=x_vals, y=y_vals, row=3, col=1)
fig.add_scatter(x=x_vals, y=y_vals, row=4, col=1)

fig.update_xaxes(spikemode='across+marker')

write_html(fig, 'out.html', auto_open=True)

The resulting figure showed spike lines across axes because only one x axis was created:

But in 4.0, multiple x axes are created so the spike line no longer draws across all subplots:

Is there any way around this? Thanks!

Start with the provided Python reproduction using make_subplots, shared_xaxes, and fig.update_xaxes(spikemode='across+marker'). Compare the generated subplot axis configuration in Plotly 4.0 with the earlier single-axis behavior. Done means identifying a supported way to make the spike line span all shared subplots, or documenting that limitation and its workaround.