diff --git a/nixos/modules/virtualisation/xen-boot-builder.sh b/nixos/modules/virtualisation/xen-boot-builder.sh
index 3fe689297864..95e363850359 100755
--- a/nixos/modules/virtualisation/xen-boot-builder.sh
+++ b/nixos/modules/virtualisation/xen-boot-builder.sh
@@ -45,28 +45,9 @@ for gen in "${gens[@]}"; do
     bootspecFile="$(sed -nr 's/^options init=(.*)\/init.*$/\1/p' "$gen")/boot.json"
     [ "$1" = "debug" ] && echo -e "\e[1;34mxenBootBuilder:\e[0m processing bootspec file $bootspecFile"
 
-    # We do nothing if the Bootspec for the current $gen does not contain the Xen
-    # extension, which is added as a configuration attribute below.
-    # We determine this by checking for the v1 or v2 bootspec extension,
-    # and setting the appropriate attributes based on version
-    xenSpecVer=""
-    xenParamVar=""
-    xenEfiPath=""
-    if grep -sq '"org.xenproject.bootspec.v1"' "$bootspecFile"; then
-        xenSpecVer="v1"
-        xenParamVar="xenParams"
-        xenEfiPath="xen"
-    fi
-    # We prefer the v2 extension, so if both are present somehow,
-    # we will use the v2 attributes
+    # Check for a valid Xen v2 spec being detected
     if grep -sq '"org.xenproject.bootspec.v2"' "$bootspecFile"; then
-        xenSpecVer="v2"
-        xenParamVar="params"
-        xenEfiPath="efiPath"
-    fi
-    # Check for a valid Xen spec being detected
-    if [ -n "$xenSpecVer" ]; then
-        [ "$1" = "debug" ] && echo -e "                \e[1;32msuccess:\e[0m found $xenSpecVer Xen entries in $gen."
+        [ "$1" = "debug" ] && echo -e "                \e[1;32msuccess:\e[0m found v2 Xen entries in $gen."
 
         # TODO: Support DeviceTree booting. Xen has some special handling for DeviceTree
         # attributes, which will need to be translated in a boot script similar to this
@@ -82,7 +63,7 @@ for gen in "${gens[@]}"; do
         # the corresponding nixos generation, substituting `nixos` with `xen`:
         # `xen-$profile-generation-$number-specialisation-$specialisation.{cfg,conf}`
         xenGen=$(echo "$gen" | sed 's_/loader/entries/nixos_/loader/entries/xen_g;s_^.*/xen_xen_g;s_.conf$__g')
-        bootParams=$(jq -re ".\"org.xenproject.bootspec.$xenSpecVer\".$xenParamVar | join(\" \")" "$bootspecFile")
+        bootParams=$(jq -re ".\"org.xenproject.bootspec.v2\".params | join(\" \")" "$bootspecFile")
         kernel=$(jq -re '."org.nixos.bootspec.v1".kernel | sub("^/nix/store/"; "") | sub("/bzImage"; "-bzImage.efi")' "$bootspecFile")
         kernelParams=$(jq -re '."org.nixos.bootspec.v1".kernelParams | join(" ")' "$bootspecFile")
         initrd=$(jq -re '."org.nixos.bootspec.v1".initrd | sub("^/nix/store/"; "") | sub("/initrd"; "-initrd.efi")' "$bootspecFile")
@@ -109,7 +90,7 @@ EOF
         # Create Xen UKI for $generation. Most of this is lifted from
         # https://xenbits.xenproject.org/docs/unstable/misc/efi.html.
         [ "$1" = "debug" ] && echo -e "\e[1;34mxenBootBuilder:\e[0m making Xen UKI..."
-        xenEfi=$(jq -re ".\"org.xenproject.bootspec.$xenSpecVer\".$xenEfiPath" "$bootspecFile")
+        xenEfi=$(jq -re ".\"org.xenproject.bootspec.v2\".efiPath" "$bootspecFile")
         finalSection=$(objdump --header --wide "$xenEfi" | tail -n +6 | sort --key="4,4" | tail -n 1 | grep -Eo '\.[a-z]*')
         padding=$(objdump --header --section="$finalSection" "$xenEfi" | awk -v section="$finalSection" '$0 ~ section { printf("0x%016x\n", and(strtonum("0x"$3) + strtonum("0x"$4) + 0xfff, compl(0xfff)))};')
         [ "$1" = "debug" ] && echo "               - padding: $padding"
@@ -132,13 +113,16 @@ sort-key $sortKey
 EOF
         [ "$1" = "debug" ] && echo -e "done."
 
-    # Sometimes, garbage collection weirdness causes a generation to still exist in
-    # the loader entries, but its Bootspec file was deleted. We consider such a
-    # generation to be invalid, but we don't write extra code to handle this
-    # situation, as supressing grep's error messages above is quite enough, and the
-    # error message below is still technically correct, as no Xen can be found in
-    # something that does not exist.
+        # Since NixOS 26.05, org.xenproject.bootspec.v1 is unsupported.
+    elif grep -sq '"org.xenproject.bootspec.v1"' "$bootspecFile"; then
+        [ "$1" = "debug" ] && echo -e "\n\e[1;33mwarning:\e[0m $gen has a \e[1;34morg.xenproject.bootspec.v1\e[0m Bootspec entry. This boot builder only supports v2 entries, so this generation will be ignored, and will \e[1;31mfail to boot\e[0m."
     else
+        # Sometimes, garbage collection weirdness causes a generation to still exist in
+        # the loader entries, but its Bootspec file was deleted. We consider such a
+        # generation to be invalid, but we don't write extra code to handle this
+        # situation, as supressing grep's error messages above is quite enough, and the
+        # error message below is still technically correct, as no Xen can be found in
+        # something that does not exist.
         [ "$1" = "debug" ] && echo -e "                \e[1;33mwarning:\e[0m \e[1;31mno Xen found\e[0m in $gen."
     fi
 done
@@ -153,7 +137,7 @@ mapfile -t postGenerations < <(find "$efiMountPoint"/loader/entries -type f -nam
 if ((${#postGenerations[@]} == 0)); then
     case "$1" in
         "default" | "info") echo "none found." && echo -e "If you believe this is an error, set the \e[1;34mvirtualisation.xen.boot.builderVerbosity\e[0m option to \e[1;34m\"debug\"\e[0m and rebuild to print debug logs." ;;
-        "debug") echo -e "\e[1;34mxenBootBuilder:\e[0m wrote \e[1;31mno generations\e[0m. Most likely, there were no generations with a valid \e[1;34morg.xenproject.bootspec.v1\e[0m or \e[1;34morg.xenproject.bootspec.v2\e[0m entry." ;;
+        "debug") echo -e "\e[1;34mxenBootBuilder:\e[0m wrote \e[1;31mno generations\e[0m. Most likely, there were no generations with a valid \e[1;34morg.xenproject.bootspec.v2\e[0m entry." ;;
     esac
 
 # If the script is successful, change the default boot, say "done.", write a
diff --git a/nixos/modules/virtualisation/xen-dom0.nix b/nixos/modules/virtualisation/xen-dom0.nix
index 92e40f77b82a..11fd5d705760 100644
--- a/nixos/modules/virtualisation/xen-dom0.nix
+++ b/nixos/modules/virtualisation/xen-dom0.nix
@@ -741,22 +741,14 @@ in
 
       # Xen Bootspec extension. This extension allows NixOS bootloaders to
       # fetch the dom0 kernel paths and access the `cfg.boot.params` option.
-      bootspec.extensions = {
-        # Bootspec extension v1 is deprecated, and will be removed in 26.05
-        # It is present for backwards compatibility
-        "org.xenproject.bootspec.v1" = {
-          xen = cfg.boot.efi.path;
-          xenParams = cfg.boot.params;
-        };
-        # Bootspec extension v2 includes more detail,
-        # including supporting multiboot, and is the current supported
-        # bootspec extension
-        "org.xenproject.bootspec.v2" = {
-          efiPath = cfg.boot.efi.path;
-          multibootPath = cfg.boot.bios.path;
-          version = cfg.package.version;
-          params = cfg.boot.params;
-        };
+      # Bootspec extension v2 includes more detail,
+      # including supporting multiboot, and is the current supported
+      # bootspec extension
+      bootspec.extensions."org.xenproject.bootspec.v2" = {
+        efiPath = cfg.boot.efi.path;
+        multibootPath = cfg.boot.bios.path;
+        version = cfg.package.version;
+        params = cfg.boot.params;
       };
 
       # See the `xenBootBuilder` script in the main `let...in` statement of this file.