That's a metric truck load of yeast. Wyeast specs their commercial cultures as having 1.2 billion viable cells per milliliter, which means that one 1L of their yeast is guaranteed to contain 1.2 trillion viable cells. I suspect that that number is very conservative. If the OP received 1L of thick slurry, man, it could contain up to 3.0 trillion viable cells. To put things in perspective, 200 billion healthy, ready to go work cells will fully attenuate 5 gallons of lager wort (yes, I know that that number is lower than the yeast calculators spec). Three trillion is 15 times 200 billion.
With that said, I would treat it like cropped slurry, see what happens on the first pitch, and adjust my pitching rate based on the fermentation outcome. My rules of thumb are 100ml of slurry per five gallons of ale wort up to around 16 Plato and 200ml of slurry per five gallons of lager wort up to around 16 Plato. It the culture is relatively new, those volumes should get the job done. Remember, the number one thing that hold brewer back when dealing with unknown yeast is fear of failure. It's only a batch of beer.
One last thing, my bank takes difficult to obtain yeast strain donations.