I am having the same issue when trying to download Metal Toolchain. Here is the info which Xcode shows after getting the error: Failed fetching catalog for assetType (com.apple.MobileAsset.MetalToolchain), serverParameters ({ RequestedBuild = 17A5295f; }) Domain: DVTDownloadsUtilitiesErrorDomain Code: -1 User Info: { DVTErrorCreationDateKey = "2025-08-07 10:56:28 +0000"; } -- Failed fetching catalog for assetType (com.apple.MobileAsset.MetalToolchain), serverParameters ({ RequestedBuild = 17A5295f; }) Domain: DVTDownloadsUtilitiesErrorDomain Code: -1 -- Download failed due to not being able to find the host. (Catalog download for com.apple.MobileAsset.MetalToolchain) Domain: com.apple.MobileAssetError.Download Code: 59 User Info: { checkConfiguration = 1; } -- System Information macOS Version 15.6 (Build 24G84) Xcode 26.0 (24198.5) (Build 17A5295f) Timestamp: 2025-08-07T13:56:28+03:00

I had a similar problem. In my case the behaviour of the isnan() was changed by the -ffast-math compiler flag. See clang.llvm.org/docs/UsersManual.html#cmdoption-ffast-math where it is stated :  This option lets the compiler make aggressive, potentially-lossy assumptions about floating-point math. These include: ... Operands to floating-point operations are not equal to NaN and Inf, and