• Reasonable exclusion of tumor or malignancy before baseline visit (randomization)

• Onset of AIE symptoms ≤ 9 months before randomization

• Meet the definition of New Onset or Incomplete Responder AIE

• For women of childbearing potential: agreement to remain abstinent (refrain from heterosexual intercourse) or use adequate contraception during the treatment period and for at least 3 months after the final dose of satralizumab or placebo

• For participants enrolled in the extended China enrollment phase at China's sites: participants who are current residents of mainland China, Hong Kong, or Taiwan, and of Chinese ancestry

⁃ NMDAR AIE Cohort:

• Age ≥ 12 years

• Diagnosis of probable or definite NMDAR encephalitis

⁃ LGI1 AIE Cohort

• Age ≥ 18 years

• Diagnosis of LGI1 encephalitis