Introduction: Optimal guideline-directed medical therapies (GDMT) improves clinical outcomes among patients with new-onset HFrEF. Limited data exist on achievement of optimal GDMT in the first 12 months among newly diagnosed patients with HFrEF. Methods: 2016-2020 OPTUM Claims Database, which includes privately insured and Medicare patients covered through the United Healthcare insurance, was used. Patients with new-onset HF were identified using validated ICD-10 codes and a 12-month look back to exclude prevalent HF. HFrEF patients were identified based on claims with ICD-10 codes of I50.2 and I50.4 within 6 months of HF diagnosis. Rates of optimal GDMT (≥50% target dose of ACEI or ARB or any dose of ARNI, ≥50% dose of beta-blocker, and any MRA) within 12 months of the incident HF diagnosis were compared overall and across race- and sex- groups. Adjusted Cox-proportional hazards models were used to evaluate the association of different patient-level factors with time to optimal GDMT during 12-month follow-up. Results: The study included 118963 patients with new-onset HFrEF (Age: 72 years, 15.8% Black, 57.4% Men). Only 8.3% achieved optimal GDMT during the 12 months after incident HF diagnosis. The optimal GDMT use within 12-months of HF diagnosis was low across the race-ethnic and gender groups ( Figure 1A/1B ). In adjusted Cox models, younger age, Black race, male sex, prevalent HF risk factors including hypertension, private (vs. Medicare insurance), and interval hospitalizations during the follow-up period were each associated with increased probability of achieving optimal GDMT ( Figure 1C ). In contrast, prevalent COPD, stroke/TIA, and polypharmacy were associated with a lower probability of achieving optimal GDMT. Conclusions: Utilization of optimal GDMT among patients with HFrEF is very low in the first 12 months after diagnosis. These findings highlight the need for aggressive implementation strategies to optimize GDMT utilization after new HF diagnosis.