Bug? Trading special techs doesn't work?

You cannot own technologies that have racial or unique requirements you do not meet. You can't trade for organic techs if you don't have the organic trait, and you can't trade for ruins techs like neural combat net unless you have found a ruin with such tech yourself. Anything telling you otherwise is incorrect.

If both empires have the trait (or have found the requisite ruins), and you still can't trade the tech, then there is a bug in that regard. Send a savegame with a bug report to se5 at malfador dot com if this is the case.

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I really would like to see colonisation techs moved in the "racial" category, so you don't accidentally trade them using the "trade all techs" treaty.

The thing is that if you have a racial tech or a unique tech at a lower level than the other party in the trade then you do get an upgrade at least.

I do however wish AI's would not trade colonization techs since having more than one colony tech is quite an edge. Far too much to just give away IMO

Because you can trade racial and unique techs like any other, provided that both parties have the required traits/ruins.

The game could attempt to check every single tech area and trait possessed by both empires and filter out the text if you don't share any, but that would be a bit process-intensive to do every time you want to make a treaty.

You could mod colony techs to require racial traits (which then requires modding every AI to take the traits), ala Colony Tech Mod of SE4. There was another way to do it sans the racial traits, by exploiting a bug in the colony tech assignment routine that ignored unique requirements, ala Colony Tech Mod 2. Not sure if #2 would work or not in SE5, but its worth a shot.

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But if you set them as a racial trait you wouldn't be able to trade colonisation techs at all, even if you wanted to, and there is already an option in game setup to forbid colonising other planet types than your own.

But what if you want to trade current techs?

I like getting the colony tech by stealing an enemy colony ship of a different tech, so trading them shouldn't be considered overpowered