Current AI Difficulty: Largest Map, FFA, Orbiting and Non-Orbiting Planets, 5 AI on Impossible Difficulty

Well, for one, impossible difficulty is meant to be impossible

Otherwise, your best chance at killing the ai, is by getting a superior economy, fast colonization, and then killing it's fleet with defence turrets, after which you can capture a few planets, and repeat the process.

Finally, it may be a good idea to play with other humans, to get to know valid strategies from other players. Make sure to check out our Saturday Event on Discord
Discord invite: https://discord.gg/sinsofasolarempire

Yes, it is possible.    I prefer to set resources, ship construction, and research speed to max.   But you didn't specify settings. Assuming everything is set to normal,  Here are some tips.  Practice until you can get 6-7 planets before the 20 minute mark.  The 'impossible' AI players have 3-4 planets at this stage, so you have a chance.

Very first thing, get your free capital ship (I prefer the Sova Carrier, but sometimes I go with the Akkan)

If loyalist, Don't build any frigates until your home garrison has 5 cobalts.  Use these and your capital ship to clear nearby planets.

If you went with the carrier, as soon as your garrison has finished producing get a colony ship

Colonize planets as fast as you can devoting resources first to eliminating underdevelopment. Then a research lab for volcanic and/or arctic colonization.  Don't bother upgrading the planets beyond the minimum to eliminate underdevelopment at this stage.  (About the time I have 5-6 planets I have enough resources to start upgrading more. 

Set garrisons to roam (under advanced planet actions)

Target the Javelis LRM Cruisers first then siege frigates.  Don't worry about the other ships, just colonize and move on, when you get more resources put up autocannon defense platforms to clear out the others. Don't bother killing or capturing derelict ships at this stage, just avoid their active range and build opposite them. 

Grab the planets with the least amount of defenses first

For level 1 research: (not necessarily in this order)

I like modular architecture and asteroid mercantile mandate. I almost never get persuasive offers and think focused exploration is even worse.

I like military grade specs, hull reinforcements, basic provisioning, advanced metallurgy, and shrikens.   I almost never get generators, radiation bomb, or jump computer.  Psidar usually comes later when I have abundant resources.

After you get garrisons, put up multiple light factories at strategic planets (the more you have the faster they produce)

Don't underestimate Autocannon Defense Platforms.  They are cheap, pack a punch and have decent HP.  They can also be spammed to create a distraction and keep a fleet from advancing. 

If you are fortunate enough to be near a NPC, get broadcast centers early to get tons of free resources.

With the current version, the Carriers are way overpowering, and on tier II to research.  Take advantage of this.

If the AI players cooperate, attack in the direction of your orbit.

The toughest game I ever played, my home planet was one asteroid away from an "impossible" AI's home planet.  The AI gets very territorial at close range.  But so do I.  I was lucky I had home planet victory on.  I got the planet between us first.  The garrison and defense platforms were enough to keep him at bay while I fast tracked a fleet of siege frigates and I quickly killed him.  Unfortunately, this distraction kept me from spreading out as much as I usually do, and the other AI captured much of the map. 

Keep in mind, it all boils down to resources.  The more you get the better.  The more efficiently you use them, the better.  The more you kill without costing you anything, the better. 

I prefer a challenge,  but man at impossible with 5 AI they good!  I like the fact that I'm struggling to even get a start on this diff as most games at highest diff are way too easy (StarCraft).

I never build defense turrets so maybe that part of why they overwhelm me.

I ended up playing a few games on nightmare and destroying all five AI, but it was a back and forth for a while.  They are getting smart attacking my planets when my fleet is gone.  Looks like they probe my outer planets to see if any fleets are there, then bring in a full fleet to destroy it if not.

I'll have to get in on the Saturday games here soon.

Good stuff.

Just a few responses from your questions:

All setting are normal and I've tried with and without orbiting planets.

1. I use a Sova to start off, 1x colony, 8x cobalts and take over my solar system with that

2. Max out commerce on each planet and start mining planet upgrade

3. Build a research station and get the planet research so I can colonize ice and volcanic

4a. Upgrade military research so I can increase supply to 1000 and start building cobalts en masse

4b. Alternative to creating a fleet... I get light factories on all planets and create garrison forces starting with the outer most planets

5. Start upgrading asteroid commerce and orbital structures discount

6.  Start upgrading military weapons and hulls

7. Die and start new game

Looks like I need to build defense turrets to fend them off maybe, but man they come with a ton of ships, including carriers.  The tech upgrades you propose are waaaaay past the point where I get killed.

Thanks!

Turrets are currently op, and are set to be nerfed. But while they are not, I recommend spamming them (the ones with advent icon).
So that is a huge thing.

Your list sounds pretty good, so I would expect it to be about how fast you perform with those tasks. 

Yeah I never used turrets in Sins 1, so I just ignored them in Sins 2.  Mistake obviously because I got through several assaults before succumbing to the AI.  Of course the little cheaters had to double team me to take me out, but we won't talk about that!

Everything's looking great.

During FFA I noticed in this version the AI sometimes has cease fire with other AI players....  They still always reject my offers so I think it's still not any option for human players.   Can somebody from development chime in and let us know if the AI has this ability or is it a bug when they don't attack each other?

When you're deciding which planets to upgrade, look a the costs and quick math ballpark the payback time.  Go with the ones that get the most bang for the buck.  Some games I'm struggling for credits, so I'll do commerce first.  But most games its the other two that I'm lacking so I usually go:

Home planet:  Mining 2, Commerce 3, Mining 3, then wait while expanding

Asteroids: Mining 1&2, Commerce 1, then wait while expanding

Volcanic: Mining 1&2, Commerce 1, Logistics 1, then wait while expanding

Ice:  Mining 1&2, Commerce 1&2, then wait while expanding

Desert:  Usually by the time I get to these it doesn't matter.  When it does I just focus on the resource I need the most.

In other words, I focus on the bare minimum to avoid penalties while in the rapid expansion phase.  After I've finished that phase, I have a better idea which resource the map isn't supplying and I'll focus one getting those.  The upgrades are quickly followed by Tier II research and orbital extraction. 

I try and time things so each planet has at least one thing in progress until it is topped off.  When I get distracted by combat and then realize I have resources, its more efficient to put one level on three different planets, not three levels on one planet.

I'm open to any other strategies, but this is the only one I've found so far that gets me the 6-7 planets by the 20 minute mark without being chewed up by underdevelopment. 

I have done the largest on ffa on all ai impossible and it seems too easy to me to be honest. But my economy is always on point so I can confirm strong economy = win against the AI.

I usually just steam roll them.