How long before Giant Gourami outgrows 150 gallon?

[Drstrangelove]

IF I use the 150g to start, but later find that I cannot get him a bigger tank, I would sell or donate him to someone that could properly house him.

Seems a tad unrealistic. This is a fish which is basically half grown when he's outgrown a 150. And while some people have had great success with them, others have posted horror stories of them going rogue.
https://www.monsterfishkeepers.com/forums/threads/giant-gouramis.53820/

Very few people have a 300-400 gallon or more tank, and of those, even fewer have stock in it that they are willing to risk or purge to add a new fish like this. Yes, it's possible, but it's not a reasonable plan.

If you have the cash, have the space and are committed to it, then sure. But it's more likely not going to end well.

Personally I love the fish because they are reportedly very personable. But I decided that I would have a properly sized tank just for them (for life) or not at all.

 

[Revan]

I picked up 3 juvie Osphronemus gouramis many years ago that were about 3"-4" at the time, and put them in a 150 gal.
Within 2 years they were pushing 15" and had easily outgrown that tank.

Thank you duanes. Good to hear from someone who's kept GG's. Not exactly what I hoped to hear, but oh well. I'll have to figure out something else.