Hi! We've been talking about these on the discord / in streams for a while, and I'm just mirroring some things that have been figured out for people who aren't in the discord.
1) 1.53 adds the new fastest truck. This version has the slowest physics so far, but the new fastest truck is faster in almost all city-city IGT categories, only exception being Edinburgh-London. This is the newly-added Volvo truck; it has higher horsepower, slightly lower weight, and has its powerband in a higher point in the rev range, all of this meaning its true top speed is 10-12km/h faster than the previous fastest truck. This truck changes nothing for challenges, all capital cities, deliveries, and city-city RTA runs as far as has been tested, as the physics in 1.53 are too much slower in slow sections for RTA runs, and you're unlikely to pull the optimal version of any truck in quick jobs.
2) Greece DLC (1.53.x onwards) adds new routing options for Istanbul-Aberdeen RTA. New routes for this category using the Greece DLC have decimated the length of the WR, making the optimal form of Istanbul-Aberdeen RTA accessible to more runners.
3) Menu layout changes make traffic despawning take longer. The graphics options have had their layout changed, and the only options which trigger a loading screen in the top page of the options lead to longer reloads and make objectionable changes to your graphics, and larger discrepancies in performance, as compared to vegetation detail. Vegetation detail has been moved to the bottom of the graphics options. This is extremely minor, and only really affects how badly IGT runs suck to run optimally.
4) Used truck dealership added. This does not appear to affect any regular category, but may affect bingos & meme speedruns.
5) Physics changes continue to make speedruns slower and more technically-difficult on newer versions.
6) Unintended launches & high-damage taps continue to be more and more common on newer versions. I'd like to remind players that getting an unintended launch usually kills your run, and often invalidates it, unless you reload a save made before the launch. I would also like to remind players that loading a save mid-run is not allowed in IGT, as it is considered a segmentation.
If I've remembered everything, all of this sums up to: most city-city IGT WRs are nearly-free for skilled runners at the time of writing (Mar 30 2025), if you can stomach finishing a run. The optimal way of playing city-city IGT is now more accessible. Finishing an optimally-played IGT run is also now significantly harder, and city-city IGT grinds are also now more soul-crushing.
We do have a couple of posts in the Guides section as well around versions but they are a bit out of date https://www.speedrun.com/ets2/guides I'm not sure what restrictions there are on people editing existing guides, but if need be I can try to update them with this information and future posts in this thread.