What the texts say. John’s prologue ends: “No man hath seen God at any time; the only begotten Son, which is in the bosom of the Father, he hath declared him” (KJV). That is the reading of the Patriarchal Text and the Byzantine tradition, ho monogenēs huios. The critical editions instead read monogenēs theos, “only-begotten God,” so that the verse speaks of the one who is himself God and is in the Father’s bosom.
The manuscript evidence. “Only-begotten God” without the article is found in the papyrus P66, the first hand of Codex Sinaiticus, Codex Vaticanus and others; with the article, in the papyrus P75 and a few more. “The only-begotten Son” is found in Codex Alexandrinus, later correctors, the great majority of later manuscripts, and the Latin tradition. The earliest witnesses clearly favour “God” (Very Strong as a description of the evidence). Many textual scholars therefore judge “God” to be original, as the older and harder reading; scribes knew the familiar Johannine phrase “only begotten Son” from John 3:16, 3:18 and 1 John 4:9 and could easily have written it here (Strong, though some scholars prefer “Son” on grounds of style and context).
What the Orthodox Church reads. The Patriarchal Text reads “the only-begotten Son,” and that is what is heard in Orthodox churches. The Orthodox faith loses nothing by either reading. The Creed confesses Christ as “the Son of God, the only-begotten, begotten of the Father before all ages … true God of true God.” Both readings of John 1:18 say what the Creed says: one calls him the only-begotten Son; the other calls him the only-begotten who is God.
How translations handle it. The KJV, NKJV, ASV, Douay-Rheims and Reina-Valera 1909 read “Son.” The NIV reads “the one and only Son, who is himself God,” and the NRSVUE “the only Son, himself God,” combining both ideas. The ESV’s 2025 text edition reads “God the only Son”; earlier editions read “the only God.” The RSV Catholic Edition reads “the only Son,” with a note that other ancient authorities read “God.”
What it does and does not change. Neither reading is a denial of Christ’s divinity. The verse already stands under John 1:1, “the Word was God.” What changes is only how directly this verse repeats it. Readers comparing Bibles here are seeing two ancient ways of confessing the same Lord.