I am 200 years in. I've had a 50-year "running" battle with the Invaders, which I was finally about to unlock my next-gen engine and laser tech to finally be able to dominate.... and then the galaxy got out-of-context'ed ;p.
By that statement though, I can infer that their tech level --IS-- advancing? That's good to know, I guess I know to go with more than 100 tech labs in my next game ;p.
(difficulty was 100%, tech was set to 50%)
Yes. Swarm tech advances with game time, since they generate throughout the game rather than having a fixed tech level at game start like Precursors or Invaders. A swarm generated after 200 years will be much higher-tech than a Swarm generated after 10 years for example.
AFAIK this is a unique mechanic as the only other spoiler race which advances in tech is the Raiders, who generate at game start and advance tech by their own unique mechanics. I'm not sure, but the Rakhas may also generate with advanced tech later in the game since they spawn in uniquely per system like the Swarm does, but I don't know since I usually avoid playing with Rakhas on.