de406 is the long-period ephemeris which is used by the Jet Propulsion Laboratory's online HORIZONS service for dates far in the past or future.
Name: DE406 (May 1997)
Years: -3000 through 3000
Report: Standish (1998) [PDF]
Size: 190 MB
This ephemeris is like DE405 but covers a longer time period. To keep its files from being too large, its size was reduced by permitting up to 1 meter of interpolation error for the position of the Moon, and 25 meters for all other solar system bodies. Since DE405 itself is often only accurate to within a few kilometers for planetary positions, the difference was not important for many users. You can get much higher accuracy from the more recent long-term ephemeris DE422 but at the cost of three times the RAM and disk space.
To compute using this ephemeris in Python, see the jplephem package.