Latest polls show Biden leading Trump by 6 points

Like normal, this poll comes down to party lines.

Rep: 91% Trump, 7% Biden

Dem: 2% Trump, 96% Biden

Which means the poll depends on their weights for Dem/Rep.

See, they assume there is some population party split like 25% Rep, 40% Dem, and 35% Ind.

Then they do the polling and might gather from the calls something like 35% Rep, 35% Dem, 30% Ind.

Then they say "oopsie, better match up our sample to the population". And weight the Rep answers less and the Dem more to bring it inline.

So like usual, these polls really all depend on what numbers they are using for the party splits at the population level. And there were some really weird ones back in 2016.

Source: Statistician, you can make data say whatever you want. We call it "interrogating the data".

Edit: I would guess they changed their weights with the new year, which prompted the shift.