Proof-theoric ordinal of ETCS

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What is the proof-theoric ordinal of Lawvere's elementary theory of the category of sets?

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The current state-of-the-art for proof-theoretic ordinals is somewhere around $\Pi^1_2$-CA$_0$, a subtheory of second-order arithmetic Z$_2$ which in turn is much weaker than ETCS. So at present this is extremely open.