Yes, liable to compulsorily registration under GST.
In one of the FAQ answered by the Government and posted on twitter also vide dated 22nd December, 2017, they have clearly stated that Export of service is an inter-state taxable supply and liable for registration.
Further clarification contact - CA SACHIN M JAIN | 8097515447 | casachinmjain @ gmail.com
EXPORT Service : As per Definition of of Export Services U/s 2(6) IGST Act ,R/w, Section 7 IGST Act , it cover Under Interstate supply.
In Term of Section 24(1)(I) : person making Interstate supply is mandatory required to obtain Registration irrespective to Threshold limit prescribed in Section 22 of CGST Act ,.. BUT AFTER ISSUED NOTIFICATION 10/2017 IGST (R) ,DATED 13/10/2017 , THERE IS NO COMPULSORY REGISTRATION FOR PERSON MAKING INTERSTATE TAXABLE SUPPLY OF SERVICES w.e.f 13/10/2017.
Hence you are not required to obtain Registration if your Aggregate Turnover is below threshold limit