How soon can we expect sub-minute resolution market data?

I would be interested in seeing sub-minute resolution data, streamed at sub-minute levels. I read that this will be implemented: will it be free as well?

Thanks

1 Min resolution is full of gaps. Less than that would be of little value.
Alpaca has to get a better Data Source first. Questrade for example has excellent data with no gaps, essp. for extended hours