What happened?

As you can see, the x tick labels on the plot show months but no year references.

Code to reproduce:

import numpy as np
import polars as pl
import altair as alt
from datetime import datetime, timedelta

start_date = datetime(2015, 9, 10)
num_days = 3695
dates = pl.date_range(
    start=start_date,
    end=start_date + timedelta(days=num_days - 1),
    interval="1d",
    eager=True,
)
price = np.ones(num_days)

df = pl.DataFrame({
    "Date": dates,
    "Data": price,
})

(
    alt.Chart(df.select(["Date", "Data"]))
    .mark_line(opacity=0.5)
    .encode(x="Date", y="Data")
    .properties(height=200, width=900)
)

What would you like to happen instead?

I can think of several options:

1. Display years slightly below months
2. Display years in between months
3. Display years in place of months

Any would work for me. 3. implies losing some granularity but maybe is simpler. Generally I think the most important value to show is the lowest frequency period that changes within the plotting window, but I haven't thought this through thoroughly.

Which version of Altair are you using?

6.0.0