diff --git a/build/hydra.nix b/build/hydra.nix
new file mode 100644
index 00000000000..595aad324ec
--- /dev/null
+++ b/build/hydra.nix
@@ -0,0 +1,186 @@
+{ inputs
+, binaryTarball
+, forAllCrossSystems
+, forAllSystems
+, lib
+, linux64BitSystems
+, nixpkgsFor
+, self
+}:
+let
+  inherit (inputs) nixpkgs nixpkgs-regression;
+  inherit (lib) fileset;
+
+  installScriptFor = tarballs:
+    nixpkgsFor.x86_64-linux.native.callPackage ../scripts/installer.nix {
+      inherit tarballs;
+    };
+
+  testNixVersions = pkgs: client: daemon:
+    pkgs.callPackage ../package.nix {
+      pname =
+        "nix-tests"
+        + lib.optionalString
+          (lib.versionAtLeast daemon.version "2.4pre20211005" &&
+           lib.versionAtLeast client.version "2.4pre20211005")
+          "-${client.version}-against-${daemon.version}";
+
+      inherit fileset;
+
+      test-client = client;
+      test-daemon = daemon;
+
+      doBuild = false;
+    };
+in
+{
+  # Binary package for various platforms.
+  build = forAllSystems (system: self.packages.${system}.nix);
+
+  shellInputs = forAllSystems (system: self.devShells.${system}.default.inputDerivation);
+
+  buildStatic = lib.genAttrs linux64BitSystems (system: self.packages.${system}.nix-static);
+
+  buildCross = forAllCrossSystems (crossSystem:
+    lib.genAttrs [ "x86_64-linux" ] (system: self.packages.${system}."nix-${crossSystem}"));
+
+  buildNoGc = forAllSystems (system:
+    self.packages.${system}.nix.override { enableGC = false; }
+  );
+
+  buildNoTests = forAllSystems (system:
+    self.packages.${system}.nix.override {
+      doCheck = false;
+      doInstallCheck = false;
+      installUnitTests = false;
+    }
+  );
+
+  # Toggles some settings for better coverage. Windows needs these
+  # library combinations, and Debian build Nix with GNU readline too.
+  buildReadlineNoMarkdown = forAllSystems (system:
+    self.packages.${system}.nix.override {
+      enableMarkdown = false;
+      readlineFlavor = "readline";
+    }
+  );
+
+  # Perl bindings for various platforms.
+  perlBindings = forAllSystems (system: nixpkgsFor.${system}.native.nix.perl-bindings);
+
+  # Binary tarball for various platforms, containing a Nix store
+  # with the closure of 'nix' package, and the second half of
+  # the installation script.
+  binaryTarball = forAllSystems (system: binaryTarball nixpkgsFor.${system}.native.nix nixpkgsFor.${system}.native);
+
+  binaryTarballCross = lib.genAttrs [ "x86_64-linux" ] (system:
+    forAllCrossSystems (crossSystem:
+      binaryTarball
+        self.packages.${system}."nix-${crossSystem}"
+        nixpkgsFor.${system}.cross.${crossSystem}));
+
+  # The first half of the installation script. This is uploaded
+  # to https://nixos.org/nix/install. It downloads the binary
+  # tarball for the user's system and calls the second half of the
+  # installation script.
+  installerScript = installScriptFor [
+    # Native
+    self.hydraJobs.binaryTarball."x86_64-linux"
+    self.hydraJobs.binaryTarball."i686-linux"
+    self.hydraJobs.binaryTarball."aarch64-linux"
+    self.hydraJobs.binaryTarball."x86_64-darwin"
+    self.hydraJobs.binaryTarball."aarch64-darwin"
+    # Cross
+    self.hydraJobs.binaryTarballCross."x86_64-linux"."armv6l-unknown-linux-gnueabihf"
+    self.hydraJobs.binaryTarballCross."x86_64-linux"."armv7l-unknown-linux-gnueabihf"
+    self.hydraJobs.binaryTarballCross."x86_64-linux"."riscv64-unknown-linux-gnu"
+  ];
+  installerScriptForGHA = installScriptFor [
+    # Native
+    self.hydraJobs.binaryTarball."x86_64-linux"
+    self.hydraJobs.binaryTarball."x86_64-darwin"
+    # Cross
+    self.hydraJobs.binaryTarballCross."x86_64-linux"."armv6l-unknown-linux-gnueabihf"
+    self.hydraJobs.binaryTarballCross."x86_64-linux"."armv7l-unknown-linux-gnueabihf"
+    self.hydraJobs.binaryTarballCross."x86_64-linux"."riscv64-unknown-linux-gnu"
+  ];
+
+  # docker image with Nix inside
+  dockerImage = lib.genAttrs linux64BitSystems (system: self.packages.${system}.dockerImage);
+
+  # Line coverage analysis.
+  coverage = nixpkgsFor.x86_64-linux.native.nix.override {
+    pname = "nix-coverage";
+    withCoverageChecks = true;
+  };
+
+  # API docs for Nix's unstable internal C++ interfaces.
+  internal-api-docs = nixpkgsFor.x86_64-linux.native.callPackage ../package.nix {
+    inherit fileset;
+    doBuild = false;
+    enableInternalAPIDocs = true;
+  };
+
+  # API docs for Nix's C bindings.
+  external-api-docs = nixpkgsFor.x86_64-linux.native.callPackage ../package.nix {
+    inherit fileset;
+    doBuild = false;
+    enableExternalAPIDocs = true;
+  };
+
+  # System tests.
+  tests = import ../tests/nixos { inherit lib nixpkgs nixpkgsFor; } // {
+
+    # Make sure that nix-env still produces the exact same result
+    # on a particular version of Nixpkgs.
+    evalNixpkgs =
+      let
+        inherit (nixpkgsFor.x86_64-linux.native) runCommand nix;
+      in
+      runCommand "eval-nixos" { buildInputs = [ nix ]; }
+        ''
+          type -p nix-env
+          # Note: we're filtering out nixos-install-tools because https://github.com/NixOS/nixpkgs/pull/153594#issuecomment-1020530593.
+          (
+            set -x
+            time nix-env --store dummy:// -f ${nixpkgs-regression} -qaP --drv-path | sort | grep -v nixos-install-tools > packages
+            [[ $(sha1sum < packages | cut -c1-40) = e01b031fc9785a572a38be6bc473957e3b6faad7 ]]
+          )
+          mkdir $out
+        '';
+
+    nixpkgsLibTests =
+      forAllSystems (system:
+        import (nixpkgs + "/lib/tests/release.nix")
+          {
+            pkgs = nixpkgsFor.${system}.native;
+            nixVersions = [ self.packages.${system}.nix ];
+          }
+      );
+  };
+
+  metrics.nixpkgs = import "${nixpkgs-regression}/pkgs/top-level/metrics.nix" {
+    pkgs = nixpkgsFor.x86_64-linux.native;
+    nixpkgs = nixpkgs-regression;
+  };
+
+  installTests = forAllSystems (system:
+    let pkgs = nixpkgsFor.${system}.native; in
+    pkgs.runCommand "install-tests"
+      {
+        againstSelf = testNixVersions pkgs pkgs.nix pkgs.pkgs.nix;
+        againstCurrentUnstable =
+          # FIXME: temporarily disable this on macOS because of #3605.
+          if system == "x86_64-linux"
+          then testNixVersions pkgs pkgs.nix pkgs.nixUnstable
+          else null;
+        # Disabled because the latest stable version doesn't handle
+        # `NIX_DAEMON_SOCKET_PATH` which is required for the tests to work
+        # againstLatestStable = testNixVersions pkgs pkgs.nix pkgs.nixStable;
+      } "touch $out");
+
+  installerTests = import ../tests/installer {
+    binaryTarballs = self.hydraJobs.binaryTarball;
+    inherit nixpkgsFor;
+  };
+}
diff --git a/flake.nix b/flake.nix
index 6356eedc0eb..6fb159d6e54 100644
--- a/flake.nix
+++ b/flake.nix
@@ -104,28 +104,6 @@
           cross = forAllCrossSystems (crossSystem: make-pkgs crossSystem "stdenv");
         });
 
-      installScriptFor = tarballs:
-        nixpkgsFor.x86_64-linux.native.callPackage ./scripts/installer.nix {
-          inherit tarballs;
-        };
-
-      testNixVersions = pkgs: client: daemon:
-        pkgs.callPackage ./package.nix {
-          pname =
-            "nix-tests"
-            + lib.optionalString
-              (lib.versionAtLeast daemon.version "2.4pre20211005" &&
-               lib.versionAtLeast client.version "2.4pre20211005")
-              "-${client.version}-against-${daemon.version}";
-
-          inherit fileset;
-
-          test-client = client;
-          test-daemon = daemon;
-
-          doBuild = false;
-        };
-
       binaryTarball = nix: pkgs: pkgs.callPackage ./scripts/binary-tarball.nix {
         inherit nix;
       };
@@ -232,156 +210,17 @@
       # 'nix.perl-bindings' packages.
       overlays.default = overlayFor (p: p.stdenv);
 
-      hydraJobs = {
-
-        # Binary package for various platforms.
-        build = forAllSystems (system: self.packages.${system}.nix);
-
-        shellInputs = forAllSystems (system: self.devShells.${system}.default.inputDerivation);
-
-        buildStatic = lib.genAttrs linux64BitSystems (system: self.packages.${system}.nix-static);
-
-        buildCross = forAllCrossSystems (crossSystem:
-          lib.genAttrs ["x86_64-linux"] (system: self.packages.${system}."nix-${crossSystem}"));
-
-        buildNoGc = forAllSystems (system:
-          self.packages.${system}.nix.override { enableGC = false; }
-        );
-
-        buildNoTests = forAllSystems (system:
-          self.packages.${system}.nix.override {
-            doCheck = false;
-            doInstallCheck = false;
-            installUnitTests = false;
-          }
-        );
-
-        # Toggles some settings for better coverage. Windows needs these
-        # library combinations, and Debian build Nix with GNU readline too.
-        buildReadlineNoMarkdown = forAllSystems (system:
-          self.packages.${system}.nix.override {
-            enableMarkdown = false;
-            readlineFlavor = "readline";
-          }
-        );
-
-        # Perl bindings for various platforms.
-        perlBindings = forAllSystems (system: nixpkgsFor.${system}.native.nix.perl-bindings);
-
-        # Binary tarball for various platforms, containing a Nix store
-        # with the closure of 'nix' package, and the second half of
-        # the installation script.
-        binaryTarball = forAllSystems (system: binaryTarball nixpkgsFor.${system}.native.nix nixpkgsFor.${system}.native);
-
-        binaryTarballCross = lib.genAttrs ["x86_64-linux"] (system:
-          forAllCrossSystems (crossSystem:
-            binaryTarball
-              self.packages.${system}."nix-${crossSystem}"
-              nixpkgsFor.${system}.cross.${crossSystem}));
-
-        # The first half of the installation script. This is uploaded
-        # to https://nixos.org/nix/install. It downloads the binary
-        # tarball for the user's system and calls the second half of the
-        # installation script.
-        installerScript = installScriptFor [
-          # Native
-          self.hydraJobs.binaryTarball."x86_64-linux"
-          self.hydraJobs.binaryTarball."i686-linux"
-          self.hydraJobs.binaryTarball."aarch64-linux"
-          self.hydraJobs.binaryTarball."x86_64-darwin"
-          self.hydraJobs.binaryTarball."aarch64-darwin"
-          # Cross
-          self.hydraJobs.binaryTarballCross."x86_64-linux"."armv6l-unknown-linux-gnueabihf"
-          self.hydraJobs.binaryTarballCross."x86_64-linux"."armv7l-unknown-linux-gnueabihf"
-          self.hydraJobs.binaryTarballCross."x86_64-linux"."riscv64-unknown-linux-gnu"
-        ];
-        installerScriptForGHA = installScriptFor [
-          # Native
-          self.hydraJobs.binaryTarball."x86_64-linux"
-          self.hydraJobs.binaryTarball."x86_64-darwin"
-          # Cross
-          self.hydraJobs.binaryTarballCross."x86_64-linux"."armv6l-unknown-linux-gnueabihf"
-          self.hydraJobs.binaryTarballCross."x86_64-linux"."armv7l-unknown-linux-gnueabihf"
-          self.hydraJobs.binaryTarballCross."x86_64-linux"."riscv64-unknown-linux-gnu"
-        ];
-
-        # docker image with Nix inside
-        dockerImage = lib.genAttrs linux64BitSystems (system: self.packages.${system}.dockerImage);
-
-        # Line coverage analysis.
-        coverage = nixpkgsFor.x86_64-linux.native.nix.override {
-          pname = "nix-coverage";
-          withCoverageChecks = true;
-        };
-
-        # API docs for Nix's unstable internal C++ interfaces.
-        internal-api-docs = nixpkgsFor.x86_64-linux.native.callPackage ./package.nix {
-          inherit fileset;
-          doBuild = false;
-          enableInternalAPIDocs = true;
-        };
-
-        # API docs for Nix's C bindings.
-        external-api-docs = nixpkgsFor.x86_64-linux.native.callPackage ./package.nix {
-          inherit fileset;
-          doBuild = false;
-          enableExternalAPIDocs = true;
-        };
-
-        # System tests.
-        tests = import ./tests/nixos { inherit lib nixpkgs nixpkgsFor; } // {
-
-          # Make sure that nix-env still produces the exact same result
-          # on a particular version of Nixpkgs.
-          evalNixpkgs =
-            let
-              inherit (nixpkgsFor.x86_64-linux.native) runCommand nix;
-            in
-            runCommand "eval-nixos" { buildInputs = [ nix ]; }
-              ''
-                type -p nix-env
-                # Note: we're filtering out nixos-install-tools because https://github.com/NixOS/nixpkgs/pull/153594#issuecomment-1020530593.
-                (
-                  set -x
-                  time nix-env --store dummy:// -f ${nixpkgs-regression} -qaP --drv-path | sort | grep -v nixos-install-tools > packages
-                  [[ $(sha1sum < packages | cut -c1-40) = e01b031fc9785a572a38be6bc473957e3b6faad7 ]]
-                )
-                mkdir $out
-              '';
-
-          nixpkgsLibTests =
-            forAllSystems (system:
-              import (nixpkgs + "/lib/tests/release.nix")
-                { pkgs = nixpkgsFor.${system}.native;
-                  nixVersions = [ self.packages.${system}.nix ];
-                }
-            );
-        };
-
-        metrics.nixpkgs = import "${nixpkgs-regression}/pkgs/top-level/metrics.nix" {
-          pkgs = nixpkgsFor.x86_64-linux.native;
-          nixpkgs = nixpkgs-regression;
-        };
-
-        installTests = forAllSystems (system:
-          let pkgs = nixpkgsFor.${system}.native; in
-          pkgs.runCommand "install-tests" {
-            againstSelf = testNixVersions pkgs pkgs.nix pkgs.pkgs.nix;
-            againstCurrentUnstable =
-              # FIXME: temporarily disable this on macOS because of #3605.
-              if system == "x86_64-linux"
-              then testNixVersions pkgs pkgs.nix pkgs.nixUnstable
-              else null;
-            # Disabled because the latest stable version doesn't handle
-            # `NIX_DAEMON_SOCKET_PATH` which is required for the tests to work
-            # againstLatestStable = testNixVersions pkgs pkgs.nix pkgs.nixStable;
-          } "touch $out");
-
-        installerTests = import ./tests/installer {
-          binaryTarballs = self.hydraJobs.binaryTarball;
-          inherit nixpkgsFor;
-        };
-
+      hydraJobs = import ./build/hydra.nix {
+        inherit
+          inputs
+          binaryTarball
+          forAllCrossSystems
+          forAllSystems
+          lib
+          linux64BitSystems
+          nixpkgsFor
+          self
+          ;
       };
 
       checks = forAllSystems (system: {