[1f60c]

Sounds like the real story should be that Google solved the halting problem. :-P

[kadoban]

You're free to solve the halting problem for restricted sets of programs, that doesn't break any rules of the universe.

They also could be just discarding any where it runs for longer than X time, or a bunch of other possibilities.

[tgv]

They might be generating programs that they know will halt. Like: applications with finite loops and such. There are not enough details.