The Wikipedia article[3] is not entirely clear and has a shocking failure to cite sources, but it claims the the Texas grid connects to the Eastern grid in two place with DC lines, and has an AC connection that has only been activated once in the Houston area.
What I suspect this is referring to is connecting to the SERC[1] area. I can't find a good source, but I suspect the existing connections are to the MRO[2].
The existing active connections are to SPP. The one inactive AC tie is to MISO I believe (which is getting one of the new HVDC ties) and yes these new connections will be to SERC (MISO and SOCO).
That means these new ties will be directly supplying the local grids of about half of the southeastern market which is a first all things considered.
That means these new ties will be directly supplying the local grids of about half of the southeastern market which is a first all things considered.