This is naturally a favorite of many English-speaking Christians, SFA, but it is not so neatly clear cut. The Greek OT Septuagint (LXX) reads as follows:
“I am the being (ego eimi)” or "I am who is."
But the Hebrew Bible says "I will be what I will be" (ehyeh asher ehyeh), or literally "I shall become who I am becoming."
The tense in LXX is present, in Hebrew it is imperfect future.
But Jesus was speaking to the Pharisees and he would have quoted the Hebrew Bible or the Targum (in Aramaic), and not in Greek.
For example, the (unofficial) Neofiti Targum (unlike the official Onkelos Targum) renders 3:14 in an exegetical manner:
"The one who said and the world came into existence from the beginning; and is to say again: Be, and it will be".
Now, targum in Hebrew means "translation" and that's what early targums were; they were freelance translations of the Hebrew text for the Aramaic speaking Jews after their return from the Babylonian captivity. They no longer spoke Hebrew but Aramaic which is like Italian is to Latin, or koine Greek is to modern Greek, or Church Slavonic is to Slavic languages - closely related but incomprehensible.
But the word Targum (capitalized) refers specifically to Aramaic translations of the Hebrew Bible (the Tanakh, i.e. the Pentutech, the Prophets and the Writings). Of these there are many, but generally the two most often used are the Onkelos (Torah, the Teaching) and the Jonathan (Ketuvim, the Prophets).
The pseudo-Jonathan and the Jerusalem Targums, the so-called "western targums," which contradict the "official Targums" render Exodus 3:14 as "He who spake, and the world was; who spake, and all things existed."
Also the 10th century Arabic translations takes the liberty of changing the the "I" into "The Eternal, who passes not away."
etc.
So, it is very clear that everything depends on which version is cherry-picked to fit the particular doctrine and that nothing in the Bible can be asserted with any certainty, except that it is closely tailored to doctrine.
Luckily for the architects of doctrine there never lacks a steady supply of fitting versions of the Bible for the task. It's like tailor-made Leggo blocks, if you get the drift.
Just something to keep in mind when considering Bible quotes and ancient quotes in general. My advice is: take them with a grain of salt. :)
“it is very clear that everything depends on which version is cherry-picked to fit the particular doctrine and that nothing in the Bible can be asserted with any certainty, except that it is closely tailored to doctrine.”
I dont think that is clear to any Christian...Catholic, Protestant or Orthodox.