Valve broke Windows XP compatibility for Portal 2 back in 2011. v4560 was the last version.

For Portal 2 v4560 on Windows XP you'll need to use the skidrow crack. You can also use just the client.dll and server.dll files from the skidrow crack with SmartSteamEmu.

I've never tried newer builds of Portal 2 with Windows XP w/onecoreAPI or API wrappers so that may be another option, the above is for vanilla XP. Portal 2 v4560 does work on Windows 2000 w/BWC with the crack though.

HL2 + EP1 + EP2 + Source + Lost Coast last I checked v5377866 (9/2019) was the last for XP.
Portal v1910503 (12/2014)

Not valve but for Black Mesa (not the standalone mod) 12/26/2019 was the last working ver ver. I faintly remember being able to use the bms folder from newer versions with the 12/26/2019 binaries on XP.

DosFreak wrote on 2023-12-03, 20:26:

Valve broke Windows XP compatibility for Portal 2 back in 2011. v4560 was the last version.

Ah, that's a shame. I assume it's gonna be a PITA to find, being as old as it is?
Regarding One Core API, I've tried to get it working on my machine earlier, and it just flat out didn't work, so I assume it wouldn't have any effect on Portal 2...

Interestingly, there seem to be people out there that did get the game working with newer builds, such as:

https://steamcommunity.com/app/620/discussion … 45825904129080/
"What happens to this game when Steam breaks on XP?" - Posted to Portal 2's community page in 2018

https://www.youtube.com/watch?v=IaDmhUlhkhU
"Gaming on Windows XP in 2019" - Portal 2 is one of the games featured here

DosFreak wrote on 2023-12-03, 20:26:

Not valve but for Black Mesa (not the standalone mod) 12/26/2019 was the last working ver.

This is not true, the latest Steam release (downloaded 2 weeks ago, again via SteamCMD) works just fine. The only issue is with the new UI, running the game with -oldgameui parameter is without any issues.

I don't currently have the version number available for BMS, all I have are the files I've saved for when I last tested and when I last tested that version worked and newer versions did not. Same with other HL2 engine based games due to Valve updates. So either what you've downloaded is an older version or the BMS team was able to fix what Valve broke.

Just because something is downloaded in 2023 or read in a forum in 2023 doesn't mean the files you downloaded are from 2023 or that people in that forum were using the latest version as of that time that they posted.......

DosFreak wrote on 2023-12-03, 20:48:

or the BMS team was able to fix what Valve broke.

Black Mesa was never affected by the HL2 updates, since it's source branch is entirely separate. As I said, the game only crashes when using the new UI, which can be disabled via -oldgameui

Think we have different opinions of working and not working and issues and without issues but if that switch works consistently on newer versions of BMS to get the game working on Windows XP then good to know.

For Portal 2 versions newer than v4560 you can see if you have any luck with the Goldberg Steam emulator, be sure to copy the ws2_32.dll and ws2_base.dll from OneCoreAPI into the same directory as the goldberg steam_api.dll file or you can use a fork of Goldberg for XP which is based off of an older version of Goldberg https://gitlab.com/this_isnotme/winxp-goldberg-emulator.
I use Goldberg on Portal 2 for Vista and above. Last tested with build v7293.