The newer stronger pirates are a feature of the new Diplomacy expansion.  Probably very few of us can answer to your satisfaction right now.  I myself plan to get Diplomacy in a few days when I have the time to play it.

What I can tell you is that in the original game and Entrenchment, pirates were considered weak fodder that weren't worth much consideration.  If anything, being attacked by them was a good thing since it allowed your capital ships to level up.  One of the features of the Diplomacy expansion pack was that pirates would get stronger and scale better with the game.  What seems to be the problem here is that pirates are scaling indefinitely and don't appear to stop improving, even after the human player has long since maxed out his fleet size and upgrades. 

There are several ways to beat pirates, but first thing it's important to understand their three huge weaknesses.  The first, and most glaring, is that they don't have shields.  Even units with small amounts of shields get a special bonus called "shield mitigation", which in effect is a 60% damage reduction.  Pirates don't have this, so they usually take more than twice as much damage as your units would take.  Their second weakness is that they will charge your defenses directly, running into very obvious death-traps.  The third weakness is that they lack a versatile fleet, neither having carriers nor support cruisers of any type.

Faced with a pirate fleet like you describe, I'd probably have three or four different defenses on hand:

1. A minefield would work wonders, whittling away a lot of their units in the first few seconds of the attack.
2. A big starbase with some repair support and enough upgrades should be able to hold unless they came with massive numbers of units.
3. Use support cruisers to disable or limit the pirates.  The guardian, subverter, and subjugator would be ideal, but hoshikos should also work.  
4. Just bite the bullet and assault the pirate base directly to end the threat for good. 

One thing I will say is that ten hour games are extraordinarily rare.  I've never played a game that ran past seven hours, personally, and I've played massive multistar games.

Haha good luck with that in Diplomacy!

To the OP:  The thing you are doing wrong is not winning the pirate bidding war.  If you fail you need to put up a strong defence or lose 1 planet, not the end of the world.  The Pirates have been beefed up to make them an actual element to the game countered by more than just a few hangers and gauss cannons.

Researching Auxilary Government can help

Well... Pirates ARE strong.

I've send following force vs pirate base:

10 capships (4 Kortuls, 2 Skinatras, 2 Vulkoras, 1 Jarrasul, 1 Marauder, all on lvl 5-7)

~50 Asilants

~25 Enforcers

~25 Overseers

~10 subverters

1 Migrator to deploy starbase

I also had:

- ALL battle-oriented artifacts (weapon buff, shield buff, hull regen buff, AM buff)

- ALL Vasari upgrades

- ALL Vasari Pacts active

- ALL Advent Pacts active

- Pirate system was under my culture

I've entered Pirate base gravwell...

There were only two pirate groups in gravwell (other were on mission)...

I've moved to border of gravwell to evade gauss cannons...

Then first group come...

More then Half on my fleet (excluding caps, they all were alive) died before second group engaged me.

Rest died just after second fleet arrived (note how "long" take passing Gravwell)...

Pirates casualties? ~40% of first group, ~5% of second group. No single gauss turret was destroyed (My plan was engaging them ater destroying enemy fleet - which didn't happen)

Well... I think Pirates are little too strong.

It need further tests, but I bet 2000+ supply fleet of fully developwed empire with all upgrades, all artifacts, all Pacts etc. etc. will not be able to take single lategame pirate base (Note pirate base I tried to destroy was not fully developed and there were only 2 pirate groups in their system...). So... It is probably OP.

I wouldn't be a fan of "infinite building" for them but I like uberpirates--simply turn the pirats active option off if they are too much?  I do like the idea of a "weak pirate" option--we could call it the "wimp setting" 

What was the pirate fleet ?! I don't have diplomacy yet and it is hard to imagine a fleet that can beat you so badly ! Was it something like 100 Kodiaks at 4k HP ?

Attacking a Pirate base can be suicide in Diplomacy. The pirates do have another weakness: Small Ships. Easily killed/mained by a Mazra missle barrage. However you really need 2 barrages, preferably from 2 Mazras to keep your losses low.

It was custom scenario with 4 pirate bases total (i had so many artifacts for a reason), and game took ~5 hours. Anyway, I had ~120 ships including 10 capships and starbase and all upgrades, artifacts, vasari pacts and advent pacts for this fleet. This fleet failed vs ~50 pirate ships... second 50 ships group just finished the job. And these pirate ships still werent on highest level...

So: I outnumbered pirate group ~2.5 times and I had almost all boosts for my ships in entire game... AND I LOST TO THIS GROUP.

Why the hell these guys don't just conquer the entire galaxy?

These pirates sound like real Buttpirates.

Darvin I understand that you are trying to bring solutions to this problem, but we are not looking for way around this, we want IC to fix the damn pirates. They are not the freaking Antarans from Master of Orion II. They are PIRATES, low level ships that are suppose to be RAIDERS and a nuisance at best, not the bringer of death/destroyer of worlds that they are right now!

I did not want to be part of the playtesters for diplomacy (like I was in Entrenchment) because I wanted to be suprised! Well guess I have to be careful what I wish for...

I wont make the same mistake twice and next time I will make sure IC hears what I have to say before the next game/expansion is released. Who playtested this???

Me.

Maybe the pirates in your neck of the woods, but over here its a way of life.

Ok on a serious note. They are not that bad. It just takes a mentality change, IMHO. Many of yall were use to use to using a few ships and/or a SB and not lose anything. Or playing a map and never losing a planet. But with all that said, I do think the rate of upgrading for the pirates is a bit high. Its brutal. And most people dont like brutal. *shrugs*

Im liking the fact I can rely on the pirates killing things. Even a Vicious AI.

I agree with this... However, I'm not sure the pirates will ever STOP increasing in strength. While there is a cap to how powerful my fleet can get it appears the pirates just keep leveling up based on some timed increment. I watched the replay just to watch the rate of increase in the pirate strength and it appeared to function on a timed basis rather than money, etc. I would actually be fine if the pirate strength was based on the money thrown at it like the pirate mission seems to imply.

Like I said in this thread and the other, it was fun, just not very believable. If you plan on playing a LONG game, you will want to take out the pirate base(s) before they get uber powerful. Otherwise they are still fairly easy to deal with with the right strategy and structures.