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It's good news, almost too good to be true.
Literal
True-[quotative-と]-[contrastive-は] cannot-think extent good news [is-だ].
Built on the ~ほど ('to the extent that...') construction, used to express degree or comparison. The phrase 本当とは思えないほど ('to the extent that one cannot think it true') conveys 'so much that it doesn't seem real' — close to English 'too good to be true.' The と is quotative (framing 本当 as the thought content), and は contrasts/emphasizes. 思えない is the potential negative of 思う ('cannot think').