It's hard to say, but if I had to take a guess on one of them I would lean towards the latter because it's highly unlikely the ORR would change it's decision on a last minute basis. If they did then we'd probably ending up waiting beyond the end of the month to find out. Eurostar meanwhile would be able to fully replace their old fleet and have some new stock left over for Frankfurt and Geneva expansion that would fill up the extra depot space at Temple Mills.The question is: is this a last minute play by Eurostar to try and influence the decision, or is it a victory lap of sorts where Eurostar are trumpeting that they have been given the depot space?
Jon Worth has another great analysis on the fleet order posted in another thread that I will drop here. It should be noted that this analysis is based on ordering 30 units with the option for 20 more, an option which by the sounds of it will be taken up by Eurostar if they get the extra capacity. It would certainly be a huge publicity risk to announce an intention for 50 trains, some of which will run to London, only to later get a stern public "No" from the ORR.
I don't want to quote the entire analysis because I don't want to clutter the thread too much, but in short Jon theorises either a full PBA and PBKA replacement only (the most likely in his opinion), a PBA and 373 replacement, including potential redeployment of the 374 fleet, or an entire old fleet replacement which he says is possible, but would seriously reduce service and capacity over time and doesn't align with Eurostar's 2030 passenger goals.
Conclusion
The most obvious way for Eurostar to deploy 30 Avelia Horizon trains is to replace the entire ex-Thalys PBA and PBKA fleet. Any attempt to deploy the new trains to London from day one results in a much more complicated rolling stock situation, with a mix of three types of trains incompatible with each other to be used across all the routes.
If Eurostar ever orders the 20 additional 200m Avelia Horizon trains, those would then most obviously replace the 8 400m long 373 trains (as 16 Avelia Horizons are needed to replace 8 373s).
And the 8 “extra” Avelia Horizon trains (from 26 to 30 in the first tranche, from 16 to 20 in the second tranche) then would be used for route expansion.