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Let $k$ be a finite field of characteristic $p > 0$, and let $X$ be a smooth proper variety over $k$. It is generally unknown whether $X$ admits a smooth proper lifting over $W(k$, where $W(k)$ denotes the ring of Witt vectors over $k$.

Instead of considering $W(k)$, let's take a finite extension $K/W(k)[1/p]$ and its ring of integers $\mathcal{O}_K$. My question is the following:

For a given variety $X$, does there necessarily exist a finite extension $K/W(k)[1/p]$ and a smooth proper variety $\tilde{X}$ over $\mathcal{O}_K$ such that $$ X \otimes_k \kappa(\mathcal{O}_K) \simeq \tilde{X} \otimes_{\mathcal{O}_K} \kappa(\mathcal{O}_K), $$ where $\kappa(\mathcal{O}_K)$ denotes the residue field of $\mathcal{O}_K$?

Additionally, if such a finite extension $K/W(k)[1/p]$ exists, would this extension necessarily be unramified?

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    $\begingroup$ No, this is not true, there are plenty examples in the literature, starting with Serre's 1961 paper. $\endgroup$ Commented Nov 8 at 9:50
  • $\begingroup$ Maybe I should add that @PiotrAchinger and Maciej Zdanowicz also have some elementary examples of non-liftable varieties. (I'm not aware of an extensive survey, but it's plausible that Oort or Liedtke or someone in this area has written something about this.) $\endgroup$ Commented Nov 8 at 12:29
  • $\begingroup$ There are certainly examples known that lift to ramified extensions but not unramified (for example I believe supersingular Enriques surfaces are examples of this). $\endgroup$
    – Will Sawin
    Commented Nov 8 at 20:29
  • $\begingroup$ I believe that already the blowing up of the graph of Frobenius in a self-product of a general type surface over a finite field does not lift to characteristic zero. Also, yes, by the analysis of moduli of Enriques surfaces by Schroeer, supersingular Enriques surfaces lift to characteristic zero, but not over the Witt vectors. $\endgroup$ Commented Nov 8 at 21:53

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