The answer is that there's no one answer.
Depends on the constitution of each bird, how many birds (for keeping each other warm) and how large or cozy the coop, how draft free, etc.......
Also depends how quickly temps plummet (or escalate) and whether there's time to acclimate. (Today temps where I am in NJ are 30 degrees less than a couple days ago - a significant shift, difficult to adjust to. In June we went from 70's one week to 110+ with heat index the next - it was really tough on the birds.)
While people had chickens years ago largely without creature comforts we cannot assume there were no cold/weather related die-offs. It's like saying wildlife is still here in the spring so the winter doesn't bother them. Truth is that only the most hardy are still here - there are plenty of die-offs over winter.
Do most chickens tolerate pretty cold weather - probably. Do all - nope. So it's a matter of observing closely our feathered friends and judging as best we can how they're feeling and providing accordingly.
JJ
Right now where I am in NJ we're having snow/hail/ice/fierce winds. Wind chill is 27, balmy for Alaska I know (brrrrrrr...can't imagine those temps!!!)! My roo and hen want NOTHING to do with any of it, and are inside bummed out! Their coop resides within a larger building - during the day they can choose to hang out outdoors or in the unheated large building or in their coop which has a heat lamp and is keeping temps above freezing......the temp differential is not so much as to be startling, but enough to give them relief if they need/want it. My roo is an older fellow and has been getting less cold tolerant. And since there's only 2 of them altogether, they don't produce much body heat. If there were a power outage I could bring them in the house if need be, clearly much more difficult a prospect for folks with umpteen chickens!