In which version of .NET will Microsoft release discriminated unions (aka type unions)?

Name: Blockcircle
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Prediction market on manifold. Microsoft has released a proposal for adding discriminated unions (aka type unions) to .NET https://github.com/dotnet/csharplang/blob/main/proposals/TypeUnions.md It is at an early stage now, in what version of .NET will it be fully released?

Liquidity: $100. Resolves: 1/1/2027.