ChtGPT says "The phrase "I slept in" typically implies that someone intentionally or unintentionally slept longer than they usually do or than they were expected to. "

@Tom If you intend to keep sleeping, you would refer to it as "sleeping in." The verb oversleep is an old one, dating from the fourteenth century, and it's related to the Old English noun oferslæp, "too much sleep."

Where? In UK usage, "sleep in" commonly means accidentally and "oversleep" is rare. In the US, "oversleep" is more common for both accidental and deliberate. If a British person slept through their alarm clock they would say they slept in; an American would probably say they overslept.

@StuartF As a Brit I would more likely use "oversleep" for accidental. Maybe this is an Americanism that has crept into my vocabulary but I don't think any Brit would find it unusual. As for the opposite, I'm thinking of that famous scene from the first Home Alone film where the (American) parents shout "WE SLEPT IN!". So while there might be more of a tendancy towards one or the other among Brits and Americans I don't think this is universal. However I will say I agree with the broad strokes that to me by default "slept in" means intentionally and "overslept" is always unintentional.

I will also say than in British English you can "have a lie-in" which is unambiguously intentional (it's often got the connotation of lying in bed relaxing without necessarily being asleep though).

@Muzer, Oxford dictionary says "lie in" is British usage and it means "sleep in" in American English oxfordlearnersdictionaries.com/definition/english/…

I agree with this answer, with the caveat that you can modify either one with "intentionally" or "accidentally" and yield varying degrees of sense without risking pure nonsense (as you would with a contradiction in terms).

@StuartF: I can't see any significant difference in the relative prevalence of sleep in vs oversleep between British and American texts, and so far as I'm concerned (as a Brit) the distinction TimR makes is exactly the same as me.

Just chiming in to say that as an American, TimR's answer is accurate to my experiences. If someone said "I slept in" with no qualifiers, I would assume it was intentional. If they said "I overslept" with no qualifiers, I would assume it was unintentional.

@StuartF I'm British, and very rarely oversleep, but I did this morning. I certainly wouldn't say that setting my alarm wrong made me sleep in. Sleeping in - if used - is more like having a lie-in, bu emphasising the actual sleep

@StuartF I can see sleep in being used for accidental situations (though I’d be unlikely to use it so myself), but I am quite confident that I have never in my life heard anyone – British or American – referring to an intentional Sunday morning lie-in as ‘oversleeping’. I can’t find any dictionaries that licence such a usage either. The prefix over- very strongly implies, or even denotes, a lack of intention. Whether you oversleep, overeat, overshare or overdo something, it is invariably not your intention.

My experience of dealing with native English speakers for over 20 years is that it's a completely agnostic idiom that's entirely dependant on context. I've found this to be consistent regardless of where the English speakers come from or which generation they are.

If my alarm clock fails to go off and I'm late for work, I will call my boss and say "I overslept." I would never say "I slept in" in that circumstance.

I've used "accidentally slept in" before. The specific context was "I had jet lag so I accidentally slept in until 2 pm." I wonder if consequences are the determiner between accidentally sleeping in and oversleeping. If I had missed a meeting I probably would have used overslept instead.

I'm really surprised that Brits would say that "slept in" was anything but a statement of intent. I know that would go down badly for an accident with an employer - "overslept" is a conciliatory term to show it was an accident. "Slept in" is always deliberate.

This answer is completely wrong (in all regions)

As a native Brit, I would say "I had a lie in" if I were doing it intentionally, or "I overslept" if it were accidental. I would never say "Slept in" under any circumstances

@Mari-LouA The noun ofer-slǽp (excessive sleep) appears in the Old English Leechdoms.

In Scottish English, "slept in" is perfectly normal for an accidental situation. It is the default phrase in my experience.

@MikeB There are probably dialect differences here as well as generational ones. For all of the 20th c. in AmE, "slept in" has referred to a deliberate choice: "Tomorrow's Saturday and I can sleep in." This dude (writing in 1919) seems to think the Scots "confuse" a lot of things :-) See Page 205. google.com/books/edition/A_Guide_to_the_English_Language/…

While I agree that ChatGPT is unreliable, at least it would provide the general opinion of a lot of people, which is how words/phrases usually get their definitions. Your answer is just one opinion, since you didn't provide any sources.

@pacoverflow - ChatGPT notoriously suffers from 'hallucinations', which means it frequently passes off completely false answers & should never be relied on to provide accurate, factual information.

@pacoverflow: But ChatGPT has no way of knowing in this instance whether the opinions it is mish-mashing are those of native speakers exclusively, and even if they are all native speakers, it has no way of knowing what dialect of English they speak. I will start giving credence to AI knowledge of language when Siri does not type "I smell a with [sic] of lavender" when I dictate "I smell a whiff of lavender". AI might be able to learn those things, but when its learning is crowd-sourced, how to keep it from devolving into ConspiracyTheoryGPT?