Can the C# using statement be written without the curly braces?

Yes, you can also put them in one using statement:

using (MemoryStream data1 = new MemoryStream(), 
                    data2 = new MemoryStream())
{
    // do stuff
}

The same rules apply when you omit the curly braces in a for or an if statement.

Incidentally if you reflect into the compiled code, the ~~compiler~~ decompiler adds the braces.

From C# 8 you can also use this syntax without any braces:

using var foo = new Foo();
var bar = foo.Bar();

foo will then be disposed at end of its scope (usually at the end of a method) - so be mindful where & when to use.

Reference - https://docs.microsoft.com/en-us/dotnet/csharp/language-reference/keywords/using-statement#example

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