Exhibit 99.1 ACELYRIN, INC. Reports Full Year 2023 Financial Results and Recent Highlights Reported positive Phase 1/2 proof-of-concept data for lonigutamab, first subcutaneous anti-IGF-1R to demonstrate clinical responses in thyroid eye disease patients Achieved primary endpoint with high statistical significance in global Phase 2b/3 clinical trial of izokibep in psoriatic arthritis with robust clinical responses also achieved for higher hurdle endpoints Announced differentiated long-term 32-week data from ...