Been seeing this often on my way home from work. Is this legal?

In some states.

In Hawaii, there's no law making lane-splitting illegal, and there's no law that explicitly allows it.

If a Cop wanted to, they could cite you for making an unsafe lane change, reckless driving, or other infraction like they would a 4-wheel driver who's zig-zagging between lanes and cutting close to other cars.  It all depends on how careful you are and whether the Cop thinks you're causing problems for other drivers.

We live in a state with laws that allow adults to ride without helmets.  Lane-splitting should be no big deal. 

I think most will say it's wrong because it's risky, but that doesn't make it unlawful -- unlike commuters using the HOV and Shoulder Lanes when they shouldn't.

A bill passed all the way through the ledge in order to make it legal under certain circumstances but Ige vetoed it.
Apparently they aren't serious about reducing emissions by encouraging people to use smaller displacement vehicles that take up less space in traffic.

The Middle St. corridor of the H-1 is one of many places where riding in between lanes would be dangerous.

The fricken lanes are so narrow.

The Freeways in California has built in lanes for motorcyclists to use to safely drive between lanes.

A bill passed all the way through the ledge in order to make it legal under certain circumstances but Ige vetoed it.
Apparently they aren't serious about reducing emissions by encouraging people to use smaller displacement vehicles that take up less space in traffic.

I was wondering what happened to that. I had been hoping it would pass but then didn't see any more coverage and forgot about it.

I don't have a motorcycle anymore but I would still support that being made legal as long as done safely.

In 1971 I was riding a Honda 750 from Torrance to Santa Barbara during rush hour traffic.  A CHP motorcycle pulls up alongside me and asks, “Howzit going?”  I tell him “Fine.”  He says “Why aren’t you splitting lanes?” I told him I was from Hawaii and it was illegal there. He said not here and pulled out between the lanes. I followed him for about 30 miles before he pulled off the freeway.  He probably saved me 45 minutes of driving time.

In 1971 I was riding a Honda 750 from Torrance to Santa Barbara during rush hour traffic.  A CHP motorcycle pulls up alongside me and asks, “Howzit going?”  I tell him “Fine.”  He says “Why aren’t you splitting lanes?” I told him I was from Hawaii and it was illegal there. He said not here and pulled out between the lanes. I followed him for about 30 miles before he pulled off the freeway.  He probably saved me 45 minutes of driving time.

I have been caught in a downpour more than once, would have saved me to be able to lane split

In CA it's common practice. Here not so much
In CA I'll be driving from SD to LA so everyone is going around 90mph, and here come a biker in between lanes goes whizzing by at at least 110 or faster. Crazy!