The main purpose of this study is to assess the long-term safety and tolerability of LY4256984 in participants with Amyotrophic Lateral Sclerosis (ALS). This study is a long-term extension of study J6I-MC-OWAA (NCT07100119) and is part of the OLMP (NCT07571200) master protocol that will last approximately 96 weeks.

Participants must meet eligibility criteria in the [L0U-MC-OLMP] screening protocol before entry into the treatment study.

Inclusion Criteria:

• Have completed the main treatment period/phase as well as any off-treatment period/phase of Study OWAA, the parent study for this ISA.

Exclusion Criteria:

• The participant has conditions that preclude a lumbar puncture (LP), such as:

  • A history of clinically significant back pain, back pathology, and/or back injury (for example, degenerative disease, spinal deformity, or spinal surgery) that may predispose to complications or technical difficulty with LP.
  • Allergy to local anesthetics, such as lidocaine or its derivatives.
  • A local infection at the intended site of the LP.
  • Less than 100 giga per liter [(<100 GI/L) is equivalent to 100,000 per cubic millimeter (100,000/mm³)] platelets or clinically significant coagulation abnormality or significant active bleeding, or
  • Currently receiving treatment with an anticoagulant, antiplatelet agent, or other drug that affects coagulation or platelet function. Low dose (according to local medical guidelines) aspirin is permitted.