Lil Durk is hanging in there despite his recent murder-for-hire arrest ... with sources telling us his only complaint is about the food on the inside.
Sources with direct knowledge tell us the Grammy-winning rapper -- who is currently locked up at the Federal Detention Center in Miami -- says he's in "great spirits" while he's going through processing.
We're told he's getting along well with the FDC Miami staff as well as his fellow inmates inside ... with those in the know describing the guy as "super charming" and "agreeable."
That said ... our sources say he hates the food -- a pretty common grievance made by those who've done time.
As for the serious criminal case he's facing, we're told Lil Durk plans on pleading not guilty and fighting the murder-for-hire conspiracy charge. No word yet on when the Federal Bureau of Prisons will send him back to California to formally face the charge.
As we told you ... Lil Durk -- who has collaborated with Future, Justin Bieber, Morgan Wallen, Young Thug, Chris Brown and Drake, among others -- was arrested last week for allegedly masterminding the murder-for-hire plot against Quando Rondo, which left Quando's cousin Saviay'a Robinson shot dead.
Prosecutors allege Durk placed the bounty on QR and helped the alleged OTF members arrested in connection to the killing procure ski masks, car rentals and hotel rooms to carry out the murder.
We've reached out to Lil Durk's attorney ... so far, no word back.