Inclusion Criteria:  Age ≥18 years. Diagnosis of ELN AML other than acute promyelocytic leukemia (APL) with t(15;17)(q22;q12) or variants of these according to the 2016 WHO classification. In first CR/CRi/CRh after at at least 2 cycles of intensive chemotherapy with MRD by l MFC-based MRD assay or qPCR mutant NPM1 assessed by central lab. Three cycles of intensive treatment is allowed if 2 cycles of treatment were needed to reach morphological remission. Should be off any active systemic therapy for AML for at least 14 days or 5 half-lives (whichever is longer) prior to study registration All Grade 2-4 non-hematologic toxicities should have resolved. Planned to undergo myeloablative or reduced intensity conditioning prior to alloHCT with a likely source for donor cells identified. Eastern Cooperative Oncology Group (ECOG)/ WHO performance status 0-2.  Adequate hepatic and renal function  Both alanine aminotransferase (ALT) and aspartate aminotransferase (AST) levels (less or equal then) 2.5 times the institutional upper limit of normal (ULN). Total bilirubin level (less or equal then) 1.5 times the ULN (unless the patient has a history of Gilbert's Syndrome, in which case, total bilirubin must be (less or equal then) 2.5 times the ULN). Serum creatinine level (less or equal then) 1.5 times the ULN or a calculated or measured creatinine clearance of ≥ 50 mL/min.  Adequate organ reserve including cardiovascular, pulmonary, renal, and hepatic functioning sufficient, in the judgment of the Investigator, to undergo therapy.  - If there is a history or signs of heart failure, an echocardiography or MUGA should be obtained, with the estimated left ventricular ejection fraction required to be ≥45%.  Women of childbearing potential must test negative for pregnancy at enrollment. Sexually active women of child-bearing potential must be willing to use a highly effective method of birth control from the time of consent through 12 weeks after flotetuzumab administration. A highly effective method is defined as those which result in a low failure rate (i.e., less than 1% per year) such as implants, injectables, combined oral contraceptives, intra-uterine devices (IUDs) or vasectomized partner. Male patients with partners of childbearing potential must be either vasectomized or agree to use a condom in addition to having their partners use another method of contraception resulting in a highly effective method of birth control defined as those which result in a low failure rate (i.e., less than 1% per year) such as implants, injectables, combined oral contraceptives, or IUDs. Patients should not have sexual intercourse with females who are either pregnant or lactating without double barrier contraception. Contraception should be employed from the time of consent through 12 weeks after flotetuzumab administration. Patient is able and willing to adhere to the study visit schedule and other protocol requirements. Patient is capable of giving informed consent. Written informed consent.  Exclusion Criteria:  Prior history of allogeneic HCT. Prior treatment with an anti-CD123-directed agent. Favorable risk AML other than AML with NPM1 mutation (according to 2017 ELN) Myeloid blast crisis of chronic myeloid leukemia (CML). Concomitant illness associated with an estimated survival of <1 year. Any active untreated autoimmune disorders (with the exception of vitiligo, resolved childhood atopic dermatitis, prior Grave's disease now euthyroid clinically and with stable supplementation).  Second primary malignancy that requires active therapy. Adjuvant hormonal therapy is allowed. Patients with the following history/concurrent conditions are allowed:  Basal or squamous cell carcinoma of the skin Carcinoma in situ of the cervix Carcinoma in situ of the breast Incidental histologic finding of prostate cancer Active systemic fungal, bacterial, viral, or other infection, unless disease is under treatment with anti-microbials, and/or controlled or stable (e.g. if specific, effective therapy is not available/feasible or desired [e.g. chronic viral hepatitis, HIV]). Patient needs to be clinically stable as defined as being afebrile and hemodynamically stable for 24 hours. Requirement, at the time of study entry, for concurrent steroids >10 mg/day of oral prednisone or the equivalent, except steroid inhaler, nasal spray or ophthalmic solution. Use of immunosuppressant medications (other than steroids as noted) in the 2 weeks prior to study drug administration. Use of granulocyte colony stimulating or granulocyte-macrophage colony stimulating factor in the 2 weeks prior to study drug administration. Known central nervous system (CNS) leukemia. Patients with suspected CNS leukemia must be evaluated by lumbar puncture and be free of CNS disease prior to study entry. Previously treated CNS leukemia is allowed provided adequate treatment has been provided and the patient is free of CNS disease. Known hypersensitivity to murine, yeast, or recombinant proteins; polysorbate 80; recombinant human serum albumin; benzyl alcohol; or any excipient contained in the flotetuzumab drug formulation. Dementia or altered mental status that would preclude sufficient understanding to provide informed consent. Pregnant or lactating female patient. Current participation in another clinical trial. Any psychological, familial, sociological and geographical condition potentially hampering compliance with the study protocol and follow-up schedule.