Is it possible to implement data classification scheme (for choropleth plot) in altair?

Question

I am creating a choropleth plot function with Altair and want to use different data classification scheme for the size of the scatter markers. I have looked up the bin parameters and bin transform in encoding but haven't worked it out. Ideally I want to implement the classification schemes like they are in GeoPandas. Here is my current code and plot (only the size part is relevant I believe)

base = alt.Chart(choro_data).mark_geoshape(
    fill="lightgray",
    stroke='white',
    strokeWidth=0.1
).properties(
    width=1000,
    height=800,
    title='Safe Graph for Average Distance'
).project(
    type='albersUsa'
)

cold = alt.Chart(choro_data).mark_circle().encode(
    latitude='properties.latitude:Q',
    longitude='properties.longitude:Q',
    stroke=alt.ColorValue("black"),
    strokeWidth = alt.value(1),
    strokeOpacity = alt.condition(
        'datum.properties.recency <= 5',   ### condition value set to??
        alt.value(1), 
        alt.value(0)),
    color=alt.Color('properties.recency:Q',
                                     bin = alt.Bin(step=5),
                                     scale=alt.Scale(scheme='blues'),
                                     legend=alt.Legend(title='Week Numbers (Cold Spots)')),
    size=alt.Size('properties.total:Q', 
                  scale=alt.Scale(range=[0, 70]),
                  bin=alt.Bin(step=5),
                  legend=alt.Legend(title='Number of Time Classified as Cold/Hot Spots')),
    tooltip=display
)

base+cold

choropleth plot