In siddurim[1] , in the passage of veshammeru, even when reported with full teamim, אוֹת הִוא לְעֹלָם is always converted to אוֹת הִיא לְעֹלָם, with the yod instead of the vav.
Why is the original text changed, even if the pronunciation is the same?
[1] I checked six: Panzieri's Italian siddur, Machazor Bologna, Piattelli/Sermoneta's Italian siddur, קול אליהו, Artscroll Aschenazi Siddur and "Tefillat Yesharim" (Sephardic)
The Minchas Shai to Bereshit 4,22 quoted here says הוא כתוב בוא"ו וקרי היא ביו"ד
It's a kri/ksiv.
The reading with the vov is the written version (ksiv) but it is always pronounced as if with a yud (kri). So the siddurim use the version which is pronounced.
BTW The Koren Sacks siddur uses one font for prayers and another (the same as in their Tanakh) for quotes from Tanakh. Because of this I was not surprised to see that the הוא there in “veshammeru” is the ksiv.
But the following all use the kri:
Even though this passage is borrowed from the Torah, ultimately this is part of the davening and not a Torah reading. Therefore, there is no reason to write it according to the exact text of the Torah and then to vowelize it correctly. And on the contrary, since the main concern here is that people should pronounce the davening correctly, it is far more practical and sensible to write the word as it is pronounced.
