Emet VeYatziv

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Tannaim and Amoraim

The berakhah of Emet VeYatziv is found already in the Mishnah although it's not part of Keriat Shema rather one of the berakhot that the כהנים said. It's found as a berakhah after Keriat Shema in the Tosefta, Yerushalmi and Bavli. In the Tosefta and Yerushalmi it says:

הקורא את שמע צריך להזכיר יציאת מצרים באמת ויציב ר' או' צריך להזכיר בה מלכות אחרים או' צריך להזכיר בה מכת בכורים וקריעת ים סוף.

In the Yerushalmi it adds:

ר' יהושע בן לוי אומר צריך להזכיר את כולן וצריך לומר צור ישראל וגואלו.

Although in the Bavli it says that one says Emet VeYatziv in Shacharit and Emet VeEmunah in Arvit, in the Yerushalmi it says "אמת ויציב של שחרית" which implies that they said Emet VeYatziv also in Arvit.¹

Geonim

During the Geonim time, in Eretz Yisrael, they said Emet VeYatziv both in Arvit and in Shacharit² while in Bavel they said it just in Shacharit.

¹ It's possible that they said the same berakhot of keriat shema in Arvit and Shacharit, see Ahavah Rabbah and Ahavat Olam.

² See Midrash Tehillim 4 which says "אמת ויציב של שחרית" and sections from the genizah from פליישר.