Inclusion Criteria:
* Male or female subjects aged 18 to 65 years (inclusive).
* clinical diagnosis of schizophrenia per the Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition, Text Revision (DSM-5-TR) (or later) criteria, at screening.
* Body Mass Index (BMI) 18.5-35.0 kg/m² at screening.
* Clinical Global Impression-Severity (CGI-S) score ≤4 at screening.
* Positive and Negative Syndrome Scale (PANSS) total score ≤75 at screening.
* Clinically stable schizophrenia on current antipsychotic medication other than cariprazine for at least 3 months prior to screening.
* Subjects must not be taking more than two antipsychotic medications.
* Able to remain at the study site for 7 days following AX251 LAI injection.
* Judged by the investigator to be physically and mentally able to participate in the study based on clinical evaluation, physical examination, electrocardiogram (ECG), and laboratory assessments.
* Willing and able to comply with study procedures.
* Agrees to use protocol-defined contraception during the study.
* Previous tolerability to oral cariprazine (1.5-6 mg) or willingness to undergo a short oral tolerability test (2-7 days) followed by washout before study drug administration.
Exclusion Criteria:
* Diagnosis of psychiatric disorders other than schizophrenia according to DSM-5-TR (e.g., schizoaffective disorder, major depressive disorder, bipolar disorder, generalized anxiety disorder, obsessive-compulsive disorder, post-traumatic stress disorder, dementia, mild neurocognitive disorder, or personality disorders), except caffeine- or tobacco-related disorders.
* Substance use disorder (including alcohol or benzodiazepines) within 180 days prior to screening, excluding caffeine and tobacco.
* History of neuroleptic malignant syndrome, seizure disorder, or clinically significant tardive dyskinesia, akathisia, or extrapyramidal symptoms.
* Clinically significant cardiovascular, hematologic, metabolic, hepatic, renal, immunologic, or neurological disease that may interfere with study participation.
* Severe hepatic impairment (Child-Pugh Class C) at screening.
* Uncontrolled hypertension.
* Clinically significant electrocardiogram abnormalities at screening.
* Severe renal impairment (estimated glomerular filtration rate \<30 mL/min).
* History of syncope or significant orthostatic hypotension at screening.
* Failure to complete required washout period (≥5 half-lives) for prohibited medications before administration of AX251 LAI.
* Current treatment with other antipsychotic long-acting injectable (LAI) therapies.
* Electroconvulsive therapy within 60 days prior to screening.
* Acute psychosis posing imminent risk to self or others.
* Acute relapse of schizophrenia at screening.
