A few comments:

    $newgrid[$x][$y] = given @.grid[$x][$y]
    {
      when 0   { 1 if $live == 3};
      when 1   { 1 if 1 <  $live < 4 }:
    } || 0;
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Is probably better written as:

$newgrid[$x][$y] = given @.grid[$x][$y] {
      when 0  { 1 if $live == 3};
      when 1  { 1 if 1 <  $live < 4 };
      default { 0 };
    };
[download]

However, the exact semantics of the given statement haven't been fully defined yet (as in, if it returns the return value of the last given), so it might not be good to rely on that. Chances are, if it is implemented as a builtin multimethod, it will, though.

? ... : is now ?? ... :.

<STDIN> should be <$*STDIN>, since filehandles are now scalars, and STDIN is a global. (<> might still default to STDIN, though.)

Pretty good tho.

Also, there are 2 working versions of life in the Perl6 compiler located in parrot/languages/perl6. (As if anyone cared. :-/)