Wrap the statement in (...) and you can drop the backslashes. See also how people split up complicated loc queries in pandas on multiple lines too.
I've not been doing Python day-to-day so I'm starting to lose my touch on all the nice little tricks.
pipeline = (
task(get_data, branch=True)
| task(step1, workers=20)
| task(step2, workers=20)
| task(step3, workers=20, multiprocess=True)
Square brackets would create a list and braces would create a set of course. The contents still can be split over different lines-- just pointing that this syntax doesn't do the same thing.