THE defining document of hip-hop’s current evolutionary state isn’t a song, or a music video or a concert. Years from now cultural archaeologists will do much better to look back over the Twitter account of the 17-year-old Chicago rapper Chief Keef, who’s been exploding, or imploding, depending on how you look at it, one short burst of text at a time.


Last month Lil JoJo, an aspiring rapper who had a feud with Chief Keef, was murdered, and afterward a message that appeared to be mocking his death was posted on Chief Keef’s Twitter account. Amid an ensuing outcry, he later suggested that his account had been hacked and proceeded to fill it up with a stream of uplifting aphorisms that were the opposite of his usual boasts, as if he had actually been hacked, but by Oprah Winfrey or Joel Osteen.


Around the same time Chief Keef, who has spent much of this year under house arrest because of gun charges, threatened the older Chicago rapper Lupe Fiasco, who in a fit of reckoning the previous week expressed grievous concerns about the younger rapper’s nihilistic music. Keef threatened on Twitter to “smack him like da lil bitch he is.” Again, after an outcry, he said his account had been hacked. Finally, also last month, Chief Keef was relieved of his Instagram account after posting, also to Twitter, a photo of himself receiving oral sex from a woman.


By any measure, this is raw, difficult-to-consume stuff. That it’s coming from one of hip-hop’s most promising young stars newly signed to a major label makes it unusually scandalous. But what’s most surprising about the situation is that it highlights the vast gap between Chief Keef and the rest of hip-hop, at least its mainstream, popular incarnation.


This atavistic behavior highlights a sea change long in the making. Hip-hop has long been associated with unvarnished truth, both by insiders looking to traffic in supposed authenticity and shock value and by critics looking to keep it at arm’s length from polite society. But that’s an outmoded value in contemporary hip-hop, which skews heavily toward the triumphant, the fantastical and the unattainable — Drake and 2 Chainz talking about stealing girlfriends, Rick Ross boasting about wealth and so on. No one’s struggling, everyone’s celebrating.


What’s notable about Chief Keef and much of the Chicago music scene that he’s come to symbolize —  known locally as drill music — is how those elements are all but absent. With rare exception this music is unmediated and raw and without bright spots, focused on anger and violence. The instinct is to call this tough, unforgiving and concrete-hard music joyless, but in truth it’s exuberant in its darkness. Most of its practitioners are young and coming into their creative own against a backdrop of outrageous violence in Chicago, particularly among young people  —   dozens of teenagers have been killed in Chicago this year  —   and often related to gangs. (There’s a long history of overlap between Chicago’s gangs and Chicago’s rap.) That their music is a symphony of ill-tempered threats shouldn’t be a surprise.


Sure, plenty of rap is like this, but rarely, in this era of hip-hop’s full assimilation into the mainstream, does it attract much attention. It’s a surprise that Chief Keef is beginning to gain traction because there’s strikingly little room for what he does in the hip-hop mainstream, which is preoccupied with success and, probably even more impossible for him, melody. Waka Flocka Flame, another rapper who shouts more than raps, and who largely eschews the pop-oriented songwriting that’s now a permanent part of the genre, is his only real peer among current rap stars, and he’s an outlier too.


Chief Keef serves as a reminder of what’s been whitewashed out of the hip-hop mainstream: a sense of the struggle bedeviling the communities that produce much of the music. For someone whose primary exposure to hip-hop comes from terrestrial radio or BET, and whose idea of a mainstream hip-hop star is Drake, Nicki Minaj, Lil Wayne or even Rick Ross, who turned darker on his most recent album, “God Forgives, I Don’t,” the single-minded roughness of Chief Keef’s music would be almost wholly foreign.


Certainly if he sticks around long enough and becomes even a little successful, the subject matter of his music will change. But for now he’s becoming known for the sort of music that rappers tend to make early in their career, when few people are paying attention. After a long climb that began with a YouTube groundswell, “I Don’t Like,” the collaboration with Lil Reese that’s the defining document of the current Chicago sound — stark, violent, happily unforgiving — has now spent a few months on the Billboard R&B/hip-hop singles chart.


In the Top 50 of the most recent incarnation of that chart not one other song deals directly with the circumstances that Keef and Reese rap about. Mostly the competition is preoccupied with love and seduction and good times that help bury older, more scarring memories. It’s possible the Keef antagonist Lupe Fiasco will disrupt this homogeneity in coming weeks. He just released “Food & Liquor II: The Great American Rap Album Pt. 1” (1st & 15th/Atlantic), a work that, for all its thematic heavy-handedness, at least does not ignore poverty or the American underclass. Lupe Fiasco is a stern and didactic teacher, but it’s arguable that Chief Keef’s music is far better at ringing warning bells.