I submitted the report, FB20260459

Update: after many attempts I have gotten it to work by doing the following: Disable system integrity protection (boot into recovery > terminal > csrutil disable) Run sudo rm -rf /System/Library/AssetsV2/com_apple_MobileAsset_MetalToolchain/ Enable system integrity protection (boot into recovery > terminal > csrutil enable) Install the toolchain Manually mount the file at /System/Library/AssetsV2/com_apple_MobileAsset_MetalToolchain/*.asset/AssetData/Restore/*.dmg As soon as I mount it, it works. Unmounting it makes it not work again. If any engineers would want to look into why that's happening, I'd be happy to help them debug this.

I'm also having issues on Xcode 26 RC. I somehow managed to get it to compile, though unsure what or how, but after a reboot it went back to being broken. I'm also unable to run sudo rm -rf /System/Library/AssetsV2/com_apple_MobileAsset_MetalToolchain/, it errors saying Operation not permitted. The folder contains two .asset folders if that's anything noteworthy.

I'm having the same issue on iOS 17.2. While the workaround does work, it's not feasible for my usecase. Would be great if Apple could fix this