Where does keep it 100 come from?
Since at least 2005, keep it 100 was used by black hip-hop artists in their songs, which suggests the phrase originates in black slang as a variant of keep it real, evidenced since the 1990s. The 100 is apparently drawn from 100% or one-hundred percent, colloquially meaning "perfect" or "of highest quality." Artists like Gucci Mane, Steve Roc, and WC helped popularize the expression.
Then, with the release of his hit album Nothing Was the Same in 2013, superstar singer Drake brought keep it 100 to an even wider, and increasingly mainstream, audience. In the song "Too Much," he raps: "Don't run from it, like H-Town in the summertime, I keep it 100." The phrase rose to further prominence in 2015 with Larry Wilmore's The Nightly Show, which featured a segment called "Keep it 100." In the segment, Wilmore asked panelists a difficult question that they had to answer truthfully—by keeping it 100.
With the rise in popularity of emoji in the 2010s, keep it 100 saw yet more life online thanks to the Hundred Points emoji, 💯, with users variously incorporating it (keep it 💯) or using it in place of the entire phrase. In fact, one of the common names for 💯 is Keep it 100.
While the slang spread in popular culture, hip-hop artists continued to use it into the 2010s, notably including Joyner Lucas's 2017 single "Keep it 100," whose video had over six-million views on YouTube as of March, 2018.
Who uses keep it 100?
Before entering mainstream colloquial speech and writing, keep it 100 was and is still used in Black English, where it's often pronounced as keep it one hunnit/d, consistent with the phonology of the dialects. The verb in the phrase behaves normally (e.g., They kept it 100 or She's keeping it 100).
Keep it 100 is used to refer to one's own integrity (e.g., I keep it 100 with my friends) or someone else's (e.g., She keeps it 100 all the time). It is also used to critique someone's lack of keeping it 100 by being fake or dishonest. Keep it 100 sometimes characterizes a thing or person as "exceptionally great."
As noted, keep it 100 is frequently paired or substituted with the 💯 emoji.
IDC who you are.. Just keep it 💯with me. Even if it hurt.
@bigplay_va, March, 2018
Why do ppl get mad when you "keep it 100"? If that's what you asked of me, why trip? The TRUTH is: you didn't want the truth at all
@ValorMusic, March, 2010
In come the troops to break up this stupid argument. For the last time, friends don't sue friends, guys. Plus, to keep it 100, by Paul and Adrienne's logic, Lisa and Ken could've definitely sued Adrienne for accusing Lisa of selling stories.
Lauren McEwen, The Baltimore Sun, February, 2013