diff --git a/pkgs/by-name/ne/nexusmods-app/package.nix b/pkgs/by-name/ne/nexusmods-app/package.nix
index 15f282dc61e9..58688dc64611 100644
--- a/pkgs/by-name/ne/nexusmods-app/package.nix
+++ b/pkgs/by-name/ne/nexusmods-app/package.nix
@@ -5,7 +5,6 @@
   desktop-file-utils,
   dotnetCorePackages,
   fetchFromGitHub,
-  fetchurl,
   imagemagick,
   lib,
   xdg-utils,
@@ -35,12 +34,6 @@ buildDotnetModule (finalAttrs: {
 
   gameHashes = callPackage ./game-hashes { };
 
-  gamesJson = fetchurl {
-    name = "games.json";
-    url = "https://web.archive.org/web/20251221212501id_/https://data.nexusmods.com/file/nexus-data/games.json";
-    hash = "sha256-OVy6b/n6n2/TdzfHCWDOTw2yai87ieki21fEp1IGamY=";
-  };
-
   enableParallelBuilding = false;
 
   # If the whole solution is published, there seems to be a race condition where
@@ -73,9 +66,9 @@ buildDotnetModule (finalAttrs: {
     substituteInPlace src/NexusMods.Games.FileHashes/NexusMods.Games.FileHashes.csproj \
       --replace-fail '$(BaseIntermediateOutputPath)games_hashes_db.zip' "$gameHashes"
 
-    # Use a pinned version of the nexus API's games.json data
+    # Use a vendored version of the nexus API's games.json data
     substituteInPlace src/NexusMods.Networking.NexusWebApi/NexusMods.Networking.NexusWebApi.csproj \
-      --replace-fail '$(BaseIntermediateOutputPath)games.json' "$gamesJson"
+      --replace-fail '$(BaseIntermediateOutputPath)games.json' ${./vendored/games.json}
 
     ${lib.optionalString finalAttrs.doCheck ''
       # For some reason these tests fail (intermittently?) with a zero timestamp
diff --git a/pkgs/by-name/ne/nexusmods-app/update-games-json.sh b/pkgs/by-name/ne/nexusmods-app/update-games-json.sh
deleted file mode 100755
index 17e15cc452f8..000000000000
--- a/pkgs/by-name/ne/nexusmods-app/update-games-json.sh
+++ /dev/null
@@ -1,78 +0,0 @@
-#!/usr/bin/env nix-shell
-#! nix-shell -i bash -p bash curl common-updater-scripts
-
-set -eu -o pipefail
-
-# Set a default attrpath to allow running this update script directly
-export UPDATE_NIX_ATTR_PATH="${UPDATE_NIX_ATTR_PATH:-"nexusmods-app"}"
-
-save_url=https://web.archive.org/save
-json_url=https://data.nexusmods.com/file/nexus-data/games.json
-self=$(realpath "$0")
-dir=$(dirname "$self")
-curl_args=(
-  "$save_url/$json_url"
-
-  --silent
-  --fail
-  --location # follow redirects
-  --head # we only need headers
-  --output /dev/null # discard body
-  --write-out '%{url_effective}'
-
-  # Format --data-urlencode as GET query params
-  --get
-  # Instruct IA not to crawl linked content
-  --data-urlencode capture_all=0
-  # Only create a snapshot if older than 1 day
-  --data-urlencode if_not_archived_within=86400
-)
-cd "$dir"/../../../../
-
-# Ask the Internet Archive to save a snapshot of `games.json`
-# We capture its 'HTTP 302 Found' redirect location
-echo "Fetching games.json Internet Archive URL" >&2
-url=$(curl "${curl_args[@]}")
-
-# Use raw replay mode to avoid rewritten links in the JSON content
-url=$(
-  sed -E 's|^https://web\.archive\.org/web/([0-9]+)/|https://web.archive.org/web/\1id_/|' \
-    <<<"$url"
-)
-
-# The query parameters are only used in the snapshot request,
-# but remain in the redirected URL. Strip them:
-url="${url%%\?*}"
-
-current_url=$(
-  nix-instantiate --eval --raw \
-    --attr "$UPDATE_NIX_ATTR_PATH.gamesJson.url"
-)
-if [ "$current_url" = "$url" ]; then
-  echo "games.json has no changes" >&2
-  exit
-fi
-
-echo "Downloading and hashing games.json" >&2
-hash=$(
-  nix --extra-experimental-features nix-command \
-    hash convert --hash-algo sha256 --to sri \
-    "$(nix-prefetch-url "$url" --type sha256)"
-)
-
-# `update-source-version` needs the package version,
-# even though we're updating the games.json source
-package_version=$(
-  nix-instantiate --eval --raw \
-    --attr "$UPDATE_NIX_ATTR_PATH.version"
-)
-
-echo "Updating games.json source" >&2
-update-source-version \
-  "$UPDATE_NIX_ATTR_PATH" \
-  "$package_version" \
-  "$hash" \
-  "$url" \
-  --ignore-same-version \
-  --source-key=gamesJson \
-  --file="$dir"/package.nix
diff --git a/pkgs/by-name/ne/nexusmods-app/update.sh b/pkgs/by-name/ne/nexusmods-app/update.sh
index 05ff0144d6f4..8f9e74304345 100755
--- a/pkgs/by-name/ne/nexusmods-app/update.sh
+++ b/pkgs/by-name/ne/nexusmods-app/update.sh
@@ -10,28 +10,15 @@ self=$(realpath "$0")
 dir=$(dirname "$self")
 cd "$dir"/../../../../
 
-current_version=$(
-  nix-instantiate --eval --raw \
-    --attr "$UPDATE_NIX_ATTR_PATH.version"
-)
+# Update vendored files
+"$dir"/vendored/update.sh
+
+# Update game_hashes_db
+UPDATE_NIX_ATTR_PATH="$UPDATE_NIX_ATTR_PATH.gameHashes" \
+  "$dir"/game-hashes/update.sh
 
 url=$(
   nix-instantiate --eval --raw \
     --attr "$UPDATE_NIX_ATTR_PATH.meta.homepage"
 )
-
 nix-update --url "$url"
-
-new_version=$(
-  nix-instantiate --eval --raw \
-    --attr "$UPDATE_NIX_ATTR_PATH.version"
-)
-
-if [ "$current_version" != "$new_version" ]; then
-  # Update games.json
-  "$dir"/update-games-json.sh
-
-  # Update game_hashes_db
-  UPDATE_NIX_ATTR_PATH="$UPDATE_NIX_ATTR_PATH.gameHashes" \
-    "$dir"/game-hashes/update.sh
-fi
diff --git a/pkgs/by-name/ne/nexusmods-app/vendored/README.md b/pkgs/by-name/ne/nexusmods-app/vendored/README.md
new file mode 100644
index 000000000000..f92cbf87e634
--- /dev/null
+++ b/pkgs/by-name/ne/nexusmods-app/vendored/README.md
@@ -0,0 +1,31 @@
+This directory contains a vendored copy of `games.json`, along with tooling to generate it.
+
+## Purpose
+
+The games data is fetched at runtime by NexusMods.App, however it is also included at build time for two reasons:
+
+1. It allows tests to run against real data.
+2. It is used as cached data, speeding up the app's initial run.
+
+It is not vital for the file to contain all games, however ideally it should contain all games _supported_ by this version of NexusMods.App.
+That way the initial run's cached data is more useful.
+
+If this file grows too large, because we are including too many games, we can patch the `csproj` build spec so that `games.json` is not used at build time.
+We would also need to patch or disable any tests that rely on it.
+
+## Generating
+
+`games.json` is generated automatically by `update.sh`, using data from [nexusmods' API][url] and the games listed in `game-ids.nix`.
+
+To add a new game to `games.json`:
+- Inspect the [nexusmods endpoint][url] to find the game's name and ID
+- Add the name and ID to `game-ids.nix`
+- Run `update.sh`
+- Commit the result
+
+> [!Note]
+> Running `update.sh` may also update the existing games, so you may wish to create two separate commits using `git add --patch`.
+> One for updating the existing data and another for adding the new game.
+
+[url]: https://data.nexusmods.com/file/nexus-data/games.json
+
diff --git a/pkgs/by-name/ne/nexusmods-app/vendored/game-ids.nix b/pkgs/by-name/ne/nexusmods-app/vendored/game-ids.nix
new file mode 100644
index 000000000000..764658cd596d
--- /dev/null
+++ b/pkgs/by-name/ne/nexusmods-app/vendored/game-ids.nix
@@ -0,0 +1,12 @@
+# This file lists games to be included in the vendored games.json file.
+# It is not critical to include all games, other than those referenced by the test suite.
+# Ideally, all games supported by the app will be included, as this can improve first-run performance.
+{
+  # keep-sorted start case=no numeric=yes
+  "Baldur's Gate 3" = 3474;
+  "Cyberpunk 2077" = 3333;
+  "Mount & Blade II: Bannerlord" = 3174;
+  "Skyrim Special Edition" = 1704;
+  "Stardew Valley" = 1303;
+  # keep-sorted end
+}
diff --git a/pkgs/by-name/ne/nexusmods-app/vendored/games.json b/pkgs/by-name/ne/nexusmods-app/vendored/games.json
new file mode 100644
index 000000000000..6d7b4767e012
--- /dev/null
+++ b/pkgs/by-name/ne/nexusmods-app/vendored/games.json
@@ -0,0 +1,72 @@
+[
+  {
+    "id": 1303,
+    "name": "Stardew Valley",
+    "name_lower": "stardew valley",
+    "forum_url": "https://forums.nexusmods.com/games/19-stardew-valley/",
+    "nexusmods_url": "https://www.nexusmods.com/stardewvalley",
+    "genre": "Simulation",
+    "file_count": 145440,
+    "downloads": 642501970,
+    "domain_name": "stardewvalley",
+    "approved_date": 1457432329,
+    "mods": 26417,
+    "collections": 1958
+  },
+  {
+    "id": 1704,
+    "name": "Skyrim Special Edition",
+    "name_lower": "skyrim special edition",
+    "forum_url": "https://forums.nexusmods.com/games/6-skyrim/",
+    "nexusmods_url": "https://www.nexusmods.com/skyrimspecialedition",
+    "genre": "RPG",
+    "file_count": 671705,
+    "downloads": 9497429062,
+    "domain_name": "skyrimspecialedition",
+    "approved_date": 1477480498,
+    "mods": 120722,
+    "collections": 4886
+  },
+  {
+    "id": 3174,
+    "name": "Mount & Blade II: Bannerlord",
+    "name_lower": "mount & blade ii: bannerlord",
+    "forum_url": "https://forums.nexusmods.com/games/9-mount-blade-ii-bannerlord/",
+    "nexusmods_url": "https://www.nexusmods.com/mountandblade2bannerlord",
+    "genre": "Strategy",
+    "file_count": 51310,
+    "downloads": 118459993,
+    "domain_name": "mountandblade2bannerlord",
+    "approved_date": 1582898627,
+    "mods": 6455,
+    "collections": 294
+  },
+  {
+    "id": 3333,
+    "name": "Cyberpunk 2077",
+    "name_lower": "cyberpunk 2077",
+    "forum_url": "https://forums.nexusmods.com/games/1-cyberpunk-2077/",
+    "nexusmods_url": "https://www.nexusmods.com/cyberpunk2077",
+    "genre": "Action",
+    "file_count": 127687,
+    "downloads": 981788054,
+    "domain_name": "cyberpunk2077",
+    "approved_date": 1607433331,
+    "mods": 18464,
+    "collections": 1613
+  },
+  {
+    "id": 3474,
+    "name": "Baldur's Gate 3",
+    "name_lower": "baldur's gate 3",
+    "forum_url": "https://forums.nexusmods.com/games/2-baldurs-gate-3/",
+    "nexusmods_url": "https://www.nexusmods.com/baldursgate3",
+    "genre": "RPG",
+    "file_count": 107598,
+    "downloads": 366648874,
+    "domain_name": "baldursgate3",
+    "approved_date": 1602863114,
+    "mods": 15345,
+    "collections": 1725
+  }
+]
diff --git a/pkgs/by-name/ne/nexusmods-app/vendored/update.sh b/pkgs/by-name/ne/nexusmods-app/vendored/update.sh
new file mode 100755
index 000000000000..ac44e25fae48
--- /dev/null
+++ b/pkgs/by-name/ne/nexusmods-app/vendored/update.sh
@@ -0,0 +1,53 @@
+#!/usr/bin/env nix-shell
+#! nix-shell -i bash -p bash curl jq
+
+set -eu -o pipefail
+
+url='https://data.nexusmods.com/file/nexus-data/games.json'
+self=$(realpath "$0")
+dir=$(dirname "$self")
+tmp=$(mktemp)
+
+cd "$dir"/../../../../../
+
+ids=$(
+  nix-instantiate --eval --json \
+    --argstr file "$dir"/game-ids.nix \
+    --expr '{file}: builtins.attrValues (import file)'
+)
+
+echo "Fetching games data" >&2
+curl "$url" \
+  --silent \
+  --show-error \
+  --location |
+  jq --argjson ids "$ids" \
+    'map(select( .id | IN($ids[]) )) | sort_by(.id)' \
+    >"$tmp"
+
+echo "Validating result" >&2
+nix-instantiate --eval --strict \
+  --argstr idsNix "$dir"/game-ids.nix \
+  --argstr gamesJson "$tmp" \
+  --expr '
+    {
+      idsNix,
+      gamesJson,
+      lib ? import <nixpkgs/lib>,
+    }:
+    let
+      ids = import idsNix;
+      games = lib.importJSON gamesJson;
+    in
+    lib.forEach games (
+      { id, name, ... }:
+      lib.throwIfNot
+        (id == ids.${name})
+        "${name}: id ${toString id} does not match ${toString ids.${name}}"
+        null
+    )
+  ' \
+  >/dev/null
+
+echo "Installing games.json to $dir" >&2
+mv --force "$tmp" "$dir"/games.json