Inclusion Criteria:  Has signed the informed consent form (ICF) and is able and willing to comply with the requirements and restrictions listed therein. Is 18 years of age or older at the time of signing the ICF. Currently meets Diagnostic and Statistical Manual of Mental Disorders, 5th Edition (DSM-5) criteria for moderate or severe opioid use disorder (OUD). Has a history of OUD as defined by documented medical history of OUD for at least 90 days immediately prior to providing informed consent.  Meets at least 1 of these criteria for high-risk opioid use at the Screening visit:  using opioids via the injection route for an average of 5 or more days per week in the last 4 weeks. using at least 500 mg IV heroin equivalent (e.g., 1250 mg intravenous (IV) morphine) or self-reported use of any dose of highly potent synthetic opioids (fentanyl and analogues excluding transdermal patches) for an average of 5 or more days per week in the last 4 weeks by any route. Is seeking medication for the treatment of OUD. Is an appropriate candidate for opioid partial-agonist medications for opioid use disorder (MOUD) in the opinion of the Investigator or medically qualified sub-Investigator. Agrees not to use buprenorphine-containing products other than those administered as part of study treatment for the duration of the treatment period. A female participant is eligible to participate if she is not pregnant, not lactating and, if of childbearing potential, agrees not to become pregnant while on the study and to use medically acceptable means of contraception while on the study).  Exclusion Criteria:  Has current diagnosis, other than OUD, requiring chronic opioid treatment. Has concurrent primary substance use disorder, as defined by DSM-5 criteria, other than opioid, tobacco, cannabis or alcohol use disorders. Meets DSM-5 criteria for severe alcohol use disorder. Has had significant traumatic injury or major surgical procedure (as defined by the Investigator) within 30 days prior to the first dose of RBP-6000 or still recovering from prior such injury or surgery. Has congenital long QT syndrome, history of prolonged QT in the 3 months prior to Screening, or history of medications or other factors that are at risk for Torsades de Pointes. Has abdominal area unsuitable for subcutaneous injections (e.g., nodules, scarring, lesions, excessive pigment). Has history of suicidal ideation within 30 days prior to informed consent or history of a suicide attempt in the 6 months prior to informed consent. Has uncontrolled intercurrent illness including, but not limited to, a medical or psychiatric illness/social situation that would limit compliance with study requirements or compromise the ability of the participant to provide written informed consent. Has any other active medical condition, organ disease or concurrent medication or treatment that may either compromise participant safety or interfere with study endpoints. Has total bilirubin ≥ 1.5 × upper limit of normal (ULN) (with direct bilirubin > 1.3 mg/dL), alanine aminotransferase (ALT) ≥ 3 × ULN, aspartate aminotransferase (AST) ≥ 3 × ULN, serum creatinine > 2 × ULN, or international normalized ratio (INR) > 1.5 × ULN at Screening. Has known allergy or hypersensitivity to buprenorphine or any component of the ATRIGEL Delivery System. Is undergoing concurrent or has had prior treatment with any long-acting form of buprenorphine-containing product in the past 2 years, or if > 2 years has a positive UDS for buprenorphine at screening; treatment with oral buprenorphine, oral naltrexone or methadone products within 14 days prior to consent; or treatment with depot naltrexone within the 3 months prior to consent. Is undergoing concurrent treatment with another investigational agent or enrollment in another clinical study (except for an observational study) or treatment with another investigational agent within 30 days prior to Screening. Is undergoing concurrent treatment with medications contraindicated for use with buprenorphine as per local prescribing information. Has any pending legal status or pending legal action that could prohibit full participation in or compliance with study procedures. Is under court order requiring treatment for OUD. Is a member of site staff and/or has a financial interest in Indivior, or is an immediate family member of either the site staff and/or Indivior employee, directly involved in the study.