diff --git a/lib/tests/modules.sh b/lib/tests/modules.sh
index 49fc8bcbafc4..aba3f08122f5 100755
--- a/lib/tests/modules.sh
+++ b/lib/tests/modules.sh
@@ -62,17 +62,17 @@ checkConfigError() {
 
 # Check boolean option.
 checkConfigOutput "false" config.enable ./declare-enable.nix
-checkConfigError 'The option .* does not exist. Definition values:\n- In .*: true' config.enable ./define-enable.nix
+checkConfigError 'The option .* does not exist. Definition values:\n\s*- In .*: true' config.enable ./define-enable.nix
 
 # Check integer types.
 # unsigned
 checkConfigOutput "42" config.value ./declare-int-unsigned-value.nix ./define-value-int-positive.nix
-checkConfigError 'A definition for option .* is not of type.*unsigned integer.*. Definition values:\n- In .*: -23' config.value ./declare-int-unsigned-value.nix ./define-value-int-negative.nix
+checkConfigError 'A definition for option .* is not of type.*unsigned integer.*. Definition values:\n\s*- In .*: -23' config.value ./declare-int-unsigned-value.nix ./define-value-int-negative.nix
 # positive
-checkConfigError 'A definition for option .* is not of type.*positive integer.*. Definition values:\n- In .*: 0' config.value ./declare-int-positive-value.nix ./define-value-int-zero.nix
+checkConfigError 'A definition for option .* is not of type.*positive integer.*. Definition values:\n\s*- In .*: 0' config.value ./declare-int-positive-value.nix ./define-value-int-zero.nix
 # between
 checkConfigOutput "42" config.value ./declare-int-between-value.nix ./define-value-int-positive.nix
-checkConfigError 'A definition for option .* is not of type.*between.*-21 and 43.*inclusive.*. Definition values:\n- In .*: -23' config.value ./declare-int-between-value.nix ./define-value-int-negative.nix
+checkConfigError 'A definition for option .* is not of type.*between.*-21 and 43.*inclusive.*. Definition values:\n\s*- In .*: -23' config.value ./declare-int-between-value.nix ./define-value-int-negative.nix
 
 # Check either types
 # types.either
@@ -125,7 +125,7 @@ checkConfigOutput 'true' "$@" ./define-enable.nix ./define-attrsOfSub-foo-enable
 set -- config.enable ./define-enable.nix ./declare-enable.nix
 checkConfigOutput "true" "$@"
 checkConfigOutput "false" "$@" ./disable-define-enable.nix
-checkConfigError "The option .*enable.* does not exist. Definition values:\n- In .*: true" "$@" ./disable-declare-enable.nix
+checkConfigError "The option .*enable.* does not exist. Definition values:\n\s*- In .*: true" "$@" ./disable-declare-enable.nix
 checkConfigError "attribute .*enable.* in selection path .*config.enable.* not found" "$@" ./disable-define-enable.nix ./disable-declare-enable.nix
 checkConfigError "attribute .*enable.* in selection path .*config.enable.* not found" "$@" ./disable-enable-modules.nix
 
@@ -142,18 +142,18 @@ checkConfigError 'infinite recursion encountered' "$@"
 
 # Check _module.check.
 set -- config.enable ./declare-enable.nix ./define-enable.nix ./define-attrsOfSub-foo.nix
-checkConfigError 'The option .* does not exist. Definition values:\n- In .*' "$@"
+checkConfigError 'The option .* does not exist. Definition values:\n\s*- In .*' "$@"
 checkConfigOutput "true" "$@" ./define-module-check.nix
 
 # Check coerced value.
 checkConfigOutput "\"42\"" config.value ./declare-coerced-value.nix
 checkConfigOutput "\"24\"" config.value ./declare-coerced-value.nix ./define-value-string.nix
-checkConfigError 'A definition for option .* is not.*string or signed integer convertible to it.*. Definition values:\n- In .*: \[ \]' config.value ./declare-coerced-value.nix ./define-value-list.nix
+checkConfigError 'A definition for option .* is not.*string or signed integer convertible to it.*. Definition values:\n\s*- In .*: \[ \]' config.value ./declare-coerced-value.nix ./define-value-list.nix
 
 # Check coerced value with unsound coercion
 checkConfigOutput "12" config.value ./declare-coerced-value-unsound.nix
-checkConfigError 'A definition for option .* is not of type .*. Definition values:\n- In .*: "1000"' config.value ./declare-coerced-value-unsound.nix ./define-value-string-bigint.nix
-checkConfigError 'unrecognised JSON value' config.value ./declare-coerced-value-unsound.nix ./define-value-string-arbitrary.nix
+checkConfigError 'A definition for option .* is not of type .*. Definition values:\n\s*- In .*: "1000"' config.value ./declare-coerced-value-unsound.nix ./define-value-string-bigint.nix
+checkConfigError 'json.exception.parse_error' config.value ./declare-coerced-value-unsound.nix ./define-value-string-arbitrary.nix
 
 # Check mkAliasOptionModule.
 checkConfigOutput "true" config.enable ./alias-with-priority.nix
@@ -169,7 +169,7 @@ checkConfigOutput "foo" config.submodule.foo ./declare-submoduleWith-special.nix
 ## shorthandOnlyDefines config behaves as expected
 checkConfigOutput "true" config.submodule.config ./declare-submoduleWith-shorthand.nix ./define-submoduleWith-shorthand.nix
 checkConfigError 'is not of type `boolean' config.submodule.config ./declare-submoduleWith-shorthand.nix ./define-submoduleWith-noshorthand.nix
-checkConfigError "You're trying to declare a value of type \`bool'\nrather than an attribute-set for the option" config.submodule.config ./declare-submoduleWith-noshorthand.nix ./define-submoduleWith-shorthand.nix
+checkConfigError "You're trying to declare a value of type \`bool'\n\s*rather than an attribute-set for the option" config.submodule.config ./declare-submoduleWith-noshorthand.nix ./define-submoduleWith-shorthand.nix
 checkConfigOutput "true" config.submodule.config ./declare-submoduleWith-noshorthand.nix ./define-submoduleWith-noshorthand.nix
 
 ## submoduleWith should merge all modules in one swoop
@@ -193,7 +193,7 @@ checkConfigOutput "true" config.submodule.enable ./declare-submoduleWith-path.ni
 checkConfigOutput "true" config.enable ./disable-recursive/main.nix
 checkConfigOutput "true" config.enable ./disable-recursive/{main.nix,disable-foo.nix}
 checkConfigOutput "true" config.enable ./disable-recursive/{main.nix,disable-bar.nix}
-checkConfigError 'The option .* does not exist. Definition values:\n- In .*: true' config.enable ./disable-recursive/{main.nix,disable-foo.nix,disable-bar.nix}
+checkConfigError 'The option .* does not exist. Definition values:\n\s*- In .*: true' config.enable ./disable-recursive/{main.nix,disable-foo.nix,disable-bar.nix}
 
 # Check that imports can depend on derivations
 checkConfigOutput "true" config.enable ./import-from-store.nix
@@ -277,7 +277,7 @@ checkConfigOutput baz config.value.nested.bar.baz ./types-anything/mk-mods.nix
 ## types.functionTo
 checkConfigOutput "input is input" config.result ./functionTo/trivial.nix
 checkConfigOutput "a b" config.result ./functionTo/merging-list.nix
-checkConfigError 'A definition for option .fun.\[function body\]. is not of type .string.. Definition values:\n- In .*wrong-type.nix' config.result ./functionTo/wrong-type.nix
+checkConfigError 'A definition for option .fun.\[function body\]. is not of type .string.. Definition values:\n\s*- In .*wrong-type.nix' config.result ./functionTo/wrong-type.nix
 checkConfigOutput "b a" config.result ./functionTo/list-order.nix
 checkConfigOutput "a c" config.result ./functionTo/merging-attrs.nix
 
diff --git a/lib/tests/release.nix b/lib/tests/release.nix
index 77e0e1af7555..815841e0a8f3 100644
--- a/lib/tests/release.nix
+++ b/lib/tests/release.nix
@@ -23,6 +23,10 @@ pkgs.runCommand "nixpkgs-lib-tests" {
     export NIX_STORE_DIR=$TEST_ROOT/store
     export PAGER=cat
     cacheDir=$TEST_ROOT/binary-cache
+
+    mkdir -p $NIX_CONF_DIR
+    echo "experimental-features = nix-command" >> $NIX_CONF_DIR/nix.conf
+
     nix-store --init
 
     cp -r ${../.} lib
diff --git a/lib/tests/sources.sh b/lib/tests/sources.sh
index 71fee719cb21..1f63cac5005a 100755
--- a/lib/tests/sources.sh
+++ b/lib/tests/sources.sh
@@ -26,7 +26,7 @@ touch {README.md,module.o,foo.bar}
 # nix-instantiate doesn't write out the source, only computing the hash, so
 # this uses the experimental nix command instead.
 
-dir="$(nix eval --raw '(with import <nixpkgs/lib>; "${
+dir="$(nix eval --impure --raw --expr '(with import <nixpkgs/lib>; "${
   cleanSource ./.
 }")')"
 (cd $dir; find) | sort -f | diff -U10 - <(cat <<EOF
@@ -37,7 +37,7 @@ EOF
 ) || die "cleanSource 1"
 
 
-dir="$(nix eval --raw '(with import <nixpkgs/lib>; "${
+dir="$(nix eval --impure --raw --expr '(with import <nixpkgs/lib>; "${
   cleanSourceWith { src = '"$work"'; filter = path: type: ! hasSuffix ".bar" path; }
 }")')"
 (cd $dir; find) | sort -f | diff -U10 - <(cat <<EOF
@@ -47,7 +47,7 @@ dir="$(nix eval --raw '(with import <nixpkgs/lib>; "${
 EOF
 ) || die "cleanSourceWith 1"
 
-dir="$(nix eval --raw '(with import <nixpkgs/lib>; "${
+dir="$(nix eval --impure --raw --expr '(with import <nixpkgs/lib>; "${
   cleanSourceWith { src = cleanSource '"$work"'; filter = path: type: ! hasSuffix ".bar" path; }
 }")')"
 (cd $dir; find) | sort -f | diff -U10 - <(cat <<EOF
diff --git a/nixos/doc/manual/from_md/release-notes/rl-2111.section.xml b/nixos/doc/manual/from_md/release-notes/rl-2111.section.xml
index d7dfcb5381cc..d0521f2db4df 100644
--- a/nixos/doc/manual/from_md/release-notes/rl-2111.section.xml
+++ b/nixos/doc/manual/from_md/release-notes/rl-2111.section.xml
@@ -15,6 +15,15 @@
   <section xml:id="sec-release-21.11-highlights">
     <title>Highlights</title>
     <itemizedlist>
+      <listitem>
+        <para>
+          Nix has been updated to version 2.4, reference its
+          <link xlink:href="https://discourse.nixos.org/t/nix-2-4-released/15822">release
+          notes</link> for more information on what has changed. The
+          previous version of Nix, 2.3.16, remains available for the
+          time being in the <literal>nix_2_3</literal> package.
+        </para>
+      </listitem>
       <listitem>
         <para>
           <literal>iptables</literal> now uses
diff --git a/nixos/doc/manual/release-notes/rl-2111.section.md b/nixos/doc/manual/release-notes/rl-2111.section.md
index 1c737542e7d2..d957cf4ac0e0 100644
--- a/nixos/doc/manual/release-notes/rl-2111.section.md
+++ b/nixos/doc/manual/release-notes/rl-2111.section.md
@@ -6,6 +6,8 @@ In addition to numerous new and upgraded packages, this release has the followin
 
 ## Highlights {#sec-release-21.11-highlights}
 
+- Nix has been updated to version 2.4, reference its [release notes](https://discourse.nixos.org/t/nix-2-4-released/15822) for more information on what has changed. The previous version of Nix, 2.3.16, remains available for the time being in the `nix_2_3` package.
+
 - `iptables` now uses `nf_tables` backend.
 
 - PHP now defaults to PHP 8.0, updated from 7.4.
diff --git a/nixos/modules/installer/tools/nix-fallback-paths.nix b/nixos/modules/installer/tools/nix-fallback-paths.nix
index cb509b7340bd..065cea470fbb 100644
--- a/nixos/modules/installer/tools/nix-fallback-paths.nix
+++ b/nixos/modules/installer/tools/nix-fallback-paths.nix
@@ -1,7 +1,7 @@
 {
-  x86_64-linux = "/nix/store/nzp4m3cmm7wawk031byh8jg4cdzjq212-nix-2.3.16";
-  i686-linux = "/nix/store/zsaza9pwim617ak15fsc31lv65b9w3in-nix-2.3.16";
-  aarch64-linux = "/nix/store/7f6z40gyd405yd50qkyzwilnqw106bx8-nix-2.3.16";
-  x86_64-darwin = "/nix/store/c43kyri67ia8mibs0id5ara7gqwlkybf-nix-2.3.16";
-  aarch64-darwin = "/nix/store/6jwhak3cvsgnbqs540n27g8pxnk427fr-nix-2.3.16";
+  x86_64-linux = "/nix/store/hapw7q1fkjxvprnkcgw9ppczavg4daj2-nix-2.4";
+  i686-linux = "/nix/store/8qlvh8pp5j8wgrzj3is2jlbhgrwgsiy9-nix-2.4";
+  aarch64-linux = "/nix/store/h48lkygcqj4hdibbdnpl67q7ks6vkrd6-nix-2.4";
+  x86_64-darwin = "/nix/store/c3mvzszvyzakvcp9spnjvsb8m2bpjk7m-nix-2.4";
+  aarch64-darwin = "/nix/store/hbfqs62r0hga2yr4zi5kc7fzhf71bq9n-nix-2.4";
 }
diff --git a/pkgs/development/haskell-modules/configuration-nix.nix b/pkgs/development/haskell-modules/configuration-nix.nix
index 5fc968ccddeb..1418a8d6fe82 100644
--- a/pkgs/development/haskell-modules/configuration-nix.nix
+++ b/pkgs/development/haskell-modules/configuration-nix.nix
@@ -935,7 +935,11 @@ self: super: builtins.intersectAttrs super {
 
   rel8 = addTestToolDepend super.rel8 pkgs.postgresql;
 
-  cachix = generateOptparseApplicativeCompletion "cachix" super.cachix;
+  cachix = generateOptparseApplicativeCompletion "cachix" (super.cachix.override { nix = pkgs.nix_2_3; });
+
+  hercules-ci-agent = super.hercules-ci-agent.override { nix = pkgs.nix_2_3; };
+  hercules-ci-cnix-expr = super.hercules-ci-cnix-expr.override { nix = pkgs.nix_2_3; };
+  hercules-ci-cnix-store = super.hercules-ci-cnix-store.override { nix = pkgs.nix_2_3; };
 
   # Enable extra optimisations which increase build time, but also
   # later compiler performance, so we should do this for user's benefit.
diff --git a/pkgs/tools/package-management/nix/default.nix b/pkgs/tools/package-management/nix/default.nix
index 7df444177c5e..277ea30e202d 100644
--- a/pkgs/tools/package-management/nix/default.nix
+++ b/pkgs/tools/package-management/nix/default.nix
@@ -213,7 +213,7 @@ in rec {
 
   nix = nixStable;
 
-  nixStable = nix_2_3;
+  nixStable = nix_2_4;
 
   nix_2_3 = callPackage common (rec {
     pname = "nix";
diff --git a/pkgs/top-level/aliases.nix b/pkgs/top-level/aliases.nix
index a320f6a29a29..399d424c59c0 100644
--- a/pkgs/top-level/aliases.nix
+++ b/pkgs/top-level/aliases.nix
@@ -590,7 +590,7 @@ mapAliases ({
   nginxUnstable = nginxMainline; # added 2018-04-25
   nilfs_utils = nilfs-utils; # added 2018-04-25
   nix-review = nixpkgs-review; # added 2019-12-22
-  nixFlakes = nix_2_4; # added 2021-05-21
+  nixFlakes = nixStable; # added 2021-05-21
   nmap_graphical = nmap-graphical;  # added 2017-01-19
   nmap-unfree = nmap; # added 2021-04-06
   nologin = shadow; # added 2018-04-25
diff --git a/pkgs/top-level/all-packages.nix b/pkgs/top-level/all-packages.nix
index 035c937afc88..e2a6f1fa42ee 100644
--- a/pkgs/top-level/all-packages.nix
+++ b/pkgs/top-level/all-packages.nix
@@ -18661,7 +18661,7 @@ with pkgs;
   nghttp2 = callPackage ../development/libraries/nghttp2 { };
   libnghttp2 = nghttp2.lib;
 
-  nix-plugins = callPackage ../development/libraries/nix-plugins {};
+  nix-plugins = callPackage ../development/libraries/nix-plugins { nix = nix_2_3; };
 
   nika-fonts = callPackage ../data/fonts/nika-fonts { };
 
@@ -32431,7 +32431,7 @@ with pkgs;
 
   nix-eval-jobs = callPackage ../tools/package-management/nix-eval-jobs { };
 
-  nix-doc = callPackage ../tools/package-management/nix-doc { };
+  nix-doc = callPackage ../tools/package-management/nix-doc { nix = nix_2_3; };
 
   nix-bundle = callPackage ../tools/package-management/nix-bundle { };
 
@@ -32453,7 +32453,7 @@ with pkgs;
 
   nix-linter = haskell.lib.justStaticExecutables (haskellPackages.nix-linter);
 
-  nixos-option = callPackage ../tools/nix/nixos-option { };
+  nixos-option = callPackage ../tools/nix/nixos-option { nix = nix_2_3; };
 
   nix-pin = callPackage ../tools/package-management/nix-pin { };
 
diff --git a/pkgs/top-level/nixpkgs-basic-release-checks.nix b/pkgs/top-level/nixpkgs-basic-release-checks.nix
index 777cce7e5e0c..350dd273fe2e 100644
--- a/pkgs/top-level/nixpkgs-basic-release-checks.nix
+++ b/pkgs/top-level/nixpkgs-basic-release-checks.nix
@@ -3,7 +3,8 @@
 pkgs.runCommand "nixpkgs-release-checks" { src = nixpkgs; buildInputs = [nix]; } ''
     set -o pipefail
 
-    export NIX_STATE_DIR=$TMPDIR
+    export NIX_STORE_DIR=$TMPDIR/store
+    export NIX_STATE_DIR=$TMPDIR/state
     export NIX_PATH=nixpkgs=$TMPDIR/barf.nix
     opts=(--option build-users-group "")
     nix-store --init
diff --git a/pkgs/top-level/python-packages.nix b/pkgs/top-level/python-packages.nix
index e38e93e1dc1d..b2cb8b9f631e 100644
--- a/pkgs/top-level/python-packages.nix
+++ b/pkgs/top-level/python-packages.nix
@@ -7492,6 +7492,7 @@ in {
   };
 
   pythonix = callPackage ../development/python-modules/pythonix {
+    nix = pkgs.nix_2_3;
     meson = pkgs.meson.override { python3 = self.python; };
   };