A Study of LY4213663 in Healthy Participants and Participants With Rheumatoid Arthritis

Inclusion Criteria:

• Have a body mass index (BMI) of 18.0 to 32.0 kilogram per square meter (kg/m²),inclusive

Part C and D Only:

• Have a body weight at least 50 kilograms and BMI within the range 18.0 to 40.0 kg/m² (inclusive) at screening

• Have a diagnosis of adult-onset RA for at least 3 months prior to screening

Exclusion Criteria:

Healthy Participants for SAD Part A and MAD Part B Only:

• Have a history or presence of cardiovascular, respiratory, hepatic,ophthalmological, renal, gastrointestinal, endocrine, hematological, neurological,or psychiatric disorders capable of significantly altering the absorption,metabolism, or elimination of drugs

Participants with RA for Parts C and D Only:

• Have Class 4 RA according to American College of Rheumatology (ACR) revised criteria

• Have a 12-lead electrocardiogram (ECG) abnormality at screening

• Have a current or recent acute active infection