Inclusion Criteria:
1. Signed and dated informed consent form.
2. Able to understand and comply with the requirements of the Study, including surgery and post-implant rehabilitation.
3. Ability to read, write, comprehend, and speak fluently in English.
4. Post-lingually deafened.
5. 18 years of age or older at the time of informed consent.
6. Good health and absence of significant comorbidities, in the opinion of the Principal Investigator.
7. At least 30 days of experience with appropriate bilaterally fit hearing aids.
8. Ear to be implanted has severe to profound hearing loss defined as pure tone average at 500, 1000, 2000 and 4000 Hz ≥ 70 dB.
9. Contralateral ear has moderately severe to profound hearing loss defined as pure tone average at 500, 1000, 2000 and 4000 Hz ≥ 60 dB.
10. Limited benefit from amplification defined as CNC monosyllabic word recognition ≤ 40% in the ear to be implanted and ≤ 60% in the contralateral ear, in the aided condition.
11. Normal middle ear function based on otoscopy and tympanometry.
12. An accessible cochlear lumen and intact cochlear nerve, and no known lesions on the auditory nerve or auditory central nervous system, on the ear to be implanted confirmed with MRI or CT scan.
Exclusion Criteria:
1. Documented duration of severe to profound hearing loss for 20 or more years.
2. Previous cochlear implantation in either ear.
3. Ossification or any other cochlear anomaly that might prevent complete insertion of the electrode array.
4. Active external or middle ear pathology (i.e., infections, tympanic membrane perforation, or ossicular chain issues) in the ear to be implanted at the time of screening or in the past 6 months, that could impact the proper functioning of the device.
5. Known history of chronic eustachian tube dysfunction.
6. Prior surgery in the middle ear, inner ear, neck, or infraclavicular region which is anticipated to prevent proper placement or function of the Acclaim CI.
7. Hearing loss/disorder of retrocochlear origin.
8. Diagnosis of auditory neuropathy.
9. Currently using other active implants that are expected to interfere with the Acclaim CI position or function.
10. Known hypersensitivity to silicone rubber, polyurethane, stainless steel, titanium, platinum, or gold.
11. Known hypersensitivity or contraindications to procedural or post-procedural medications that cannot be adequately managed medically.
12. Pregnancy at the time of Acclaim CI implantation.
13. Known need for MRI or ionizing radiation treatment during Study participation.
14. Unrealistic expectations on the Participant's part regarding the possible benefits, risks, and limitations inherent to the surgical procedure and use of the Acclaim CI, in the Principal Investigator's opinion.
15. Unwillingness or inability to comply with all investigational requirements.
16. Additional conditions that would prevent completion of all Study requirements, in the opinion of the Principal Investigator.
17. Participation in an investigational drug study or another device study within 3 months of the Screening Visit.
18. Previous history of meningitis.
19. Deafness, in the ear to be implanted, due to:
1. a damaged or absent tympanic membrane,
2. a damaged or absent middle ear,
3. an absent cochlea,
4. lesions on the acoustic nerve, or
5. lesions on the central auditory pathway
