An Outside Context Problem was the sort of thing most civilisations encountered just once, and which they tended to encounter rather in the same way a sentence encountered a full stop.

The Excession is something from an older universe. While its intentions and background are somewhat unclear it is easily the most powerful ship/vessel we see in the Culture series.

Weapons

• Creates a massive Gridfire Incursion. At a minimum it was at least going to be 30 light years long (Sleeper came to a halt 30 LY from its position after the Excession had stopped the Incursion). And at a minimum was expanding at ~.2 LY/s or 6700000c (it would have taken 140 seconds to reach Sleeper and Sleeper was further than 30 light years away. It also would have destroyed Sleeper's fleet which at least by the time it stopped was arrayed in a light radius around Sleeper..

  • An older Culture General System Vehicle (think like a flying city that can carry millions to billions of people though in this context more of a flying military base/shipyard as it is configured for war) combination of Gridfire and CAM (Collapsed Anti-Matter) destroys Vavatch which is a fourteen million kilometer diameter ring. The reason why I include this as it is literally the only time we actually see Gridfire hit something in the series
  • Despite being capable of dealing with getting hit by a supernova (if handled properly) a Culture General Contact Unit (a Ship, sort of the Culture's equivalent of the USS Enterprise from Star Trek) compares them getting hit by it to an ancient rocket falling into the sun or a wooden ship getting hit by an atomic blast.
  • A Culture Human who had moments before been connected to a Ship's sensors makes the comparison that as a burning log is to a nuclear weapon, a fusion bomb is to the Gridfire. Hard to know exactly how accurate this is though.

• It is speculated that it might be possible for the Excession to cover the entire universe in Gridfire. Though obviously that doesn't happen.

• Damages an old Culture Ship's engine by unknown means without them noticing.

  • Probably damages a different (much more advanced) ship's engine.

Subversion/Mental Manipulation

• Takes over a Drone then uses that Drone to take over a Ship.

• Easily overwhelms and takes over an Elencher Ship.

  • Elench comparable to Culture.
  • Said ship's mind was taken over in less than a second.

• Implied to have messed with the human crew, drones and Problem Child (AI) so that after a century or so almost all the humans have auto-euthanized and the drones/AI have disappeared.

• Somehow gets GCU Grey Area's Mindstate before it is destroyed by falling into the Grid.

Speed/Mobility

• The Excession grabs a GCU then moves it over 30 light years away in under a picosecond as well as moves "near the speed of hyperlight". It also retreats fast enough the GCU's sensors can't track it. That means it is either just moving ridiculously fast or it exceeds the speed of hyperspace light.

  • Hyper light speed is variable ranging from taking a few minutes to go several light decades.
  • To allowing for a real time link between things 20,000 light years apart.

• Messes with a Culture Ship Displacement (there version of teleportation) wormholes after it tries to destroy a drone that was flying back from the Excession.

• With the ability to link between both sides of the grid the Excession is able to move between universes.

• Like Culture ships should be able to move in four dimensions though other than grabbing GCU Fate Amenable To Change (who was in hyperspace at the time) we don't ever really see it move.

Durability

• The Excession never gets touched in the entire novel. So beyond speculating that because it is considered to be "a level of power orders of magnitude beyond what any known Involved currently possesses." it is probably more durable than any ship from one of the Involved (The Culture being one of the Involved) I don't have much.

• It is able to selectively bends signals around itself so that they do not reach it and it appears they continue going past it as if it wasn't there. This ought to be able to apply to things like lasers? But it again is speculation.

• Though in the initial analysis of it by the Culture it might be made out of antimatter which would make it "vulnerable" to mutual antihalation with normal matter. Though it does mass 8e11 tons so it might take a fair amount.

Miscellaneous

• No effect on space time.

• Completely blocks an old (well before the first book in the series) Culture ship's sensors. Possibly over 50 trillion years old and also moves a trillion year old star.

• A Drone speculates that it might be possible if the Excession were to travel to a very young universe it could shape its primary characteristics how ever it wants.

• Prevents GCU Fate Amenable To Change from pushing off the Gird (effectively rendering it without engines) and also loops any signals it sends out back to itself.

• It creates a 30 LY exclusion zone around it where attempting to enter interferes with a Culture Ship's engines.