John 1:18: theos is the original reading.
Wide Geographical Distribution
The following manuscripts support theos:
Papyrus 66 [Papyrus Bodmer II ](AD 200)
Papyrus 75 (AD 175-225)
Diatessaron ("Out of Four") of Titan the Syrian [Arabic version] (c. 160-175)
Syriac Peshitta (AD 150)
Adysh manuscript (AD 897)-Gregordian-Georgian/Iberian version
Opiza manuscript (AD 913)
Tbet’ manuscript (AD 995)
Minuscule 423 (AD 1556)
Bohairic Coptic [Codex Bodmer III] (AD 300)
Codex B- Sinaiticus (c. 330–360)
Codex A- Vaticanus (c. 325–350)
Codex D- Cantabrigiensis[ Greek-Latin diglot] (c.400)
Apostolic Constitutions (AD 375 -380)
Codex Regius (AD 701-800)
Existed in 2nd century
Used by church fathers (both Greek and Latin Fathers):
Irenaeus, Clement ,Eusebius, Basil, Cyril, and Origen, Didymus, Epiphanius, Eusebius, Gregory-Nyssa, Heracleon, Hilary, Irenaeus, Jerome, Origen, Ps-Ignatius, Ptolemy, Serapion, Synesius, Tatian, Theodotus, Valentinius, and Arius.
Earliest best and ancient mss:
The Coptic versions is one of the earliest versions of the NT where huios is completely absent.
Unitarian objection: The reading "only birthed God" means there are two Gods, the one begotten and the other the begetter.
Refutation: The reading monogenes theos does not in any way disprove that God is one (monotheism).