diff --git a/doc/manual/rl-next/remove-xp-derivations.md b/doc/manual/rl-next/remove-xp-derivations.md
new file mode 100644
index 000000000..4d6b6ce2c
--- /dev/null
+++ b/doc/manual/rl-next/remove-xp-derivations.md
@@ -0,0 +1,14 @@
+---
+synopsis: Remove impure derivations
+issues: [fj#815]
+cls: [3210]
+significance: significant
+category: "Breaking Changes"
+credits: [horrors]
+---
+
+The `impure-derivations` experimental feature has been removed. New impure
+derivations cannot be created from this point forward, and existing impure store
+derivations canot be read or built any more. Derivation outputs created by
+building an impure derivation are still valid until garbage collected; existing
+impure store derivations can only be garbage collected.
diff --git a/lix/libexpr/fetchurl.nix b/lix/libexpr/fetchurl.nix
index 50007c738..670114058 100644
--- a/lix/libexpr/fetchurl.nix
+++ b/lix/libexpr/fetchurl.nix
@@ -34,6 +34,7 @@
   executable ? false,
   unpack ? false,
   name ? baseNameOf (toString url),
+  # still translates to __impure to trigger derivationStrict error checks.
   impure ? false,
 }:
 
diff --git a/lix/libutil/config.cc b/lix/libutil/config.cc
index 713b1b964..8e5912081 100644
--- a/lix/libutil/config.cc
+++ b/lix/libutil/config.cc
@@ -364,8 +364,7 @@ template<> ExperimentalFeatures BaseSetting<ExperimentalFeatures>::parse(const s
                 static std::once_flag warned;
                 warnDeprecated294(warned, s);
             } else if (*thisXpFeature == Xp::ImpureDerivations) {
-                static std::once_flag warned;
-                warnDeprecated294(warned, s);
+                throw Error("impure derivations are no longer supported");
             }
             res = res | thisXpFeature.value();
         } else
diff --git a/tests/functional/impure-derivations.nix b/tests/functional/impure-derivations.nix
index 98547e6c1..4514cbe50 100644
--- a/tests/functional/impure-derivations.nix
+++ b/tests/functional/impure-derivations.nix
@@ -2,22 +2,6 @@ with import ./config.nix;
 
 rec {
 
-  impure = mkDerivation {
-    name = "impure";
-    outputs = [ "out" "stuff" ];
-    buildCommand =
-      ''
-        echo impure
-        x=$(< $TEST_ROOT/counter)
-        mkdir $out $stuff
-        echo $x > $out/n
-        ln -s $out/n $stuff/bla
-        printf $((x + 1)) > $TEST_ROOT/counter
-      '';
-    __impure = true;
-    impureEnvVars = [ "TEST_ROOT" ];
-  };
-
   impureOnImpure = mkDerivation {
     name = "impure-on-impure";
     buildCommand =
diff --git a/tests/functional/impure-derivations.sh b/tests/functional/impure-derivations.sh
deleted file mode 100644
index 38be4234e..000000000
--- a/tests/functional/impure-derivations.sh
+++ /dev/null
@@ -1,65 +0,0 @@
-source common.sh
-
-requireDaemonNewerThan "2.8pre20220311"
-
-enableFeatures "ca-derivations impure-derivations"
-restartDaemon
-
-clearStore
-
-# Basic test of impure derivations: building one a second time should not use the previous result.
-printf 0 > $TEST_ROOT/counter
-
-# `nix derivation add` with impure derivations work
-drvPath=$(nix-instantiate ./impure-derivations.nix -A impure)
-nix derivation show $drvPath | jq .[] > $TEST_HOME/impure-drv.json
-drvPath2=$(nix derivation add < $TEST_HOME/impure-drv.json)
-[[ "$drvPath" = "$drvPath2" ]]
-
-# But only with the experimental feature!
-expectStderr 1 nix derivation add < $TEST_HOME/impure-drv.json --experimental-features nix-command | grepQuiet "experimental Lix feature 'impure-derivations' is disabled"
-
-nix build --dry-run --json --file ./impure-derivations.nix impure.all
-json=$(nix build -L --no-link --json --file ./impure-derivations.nix impure.all)
-path1=$(echo $json | jq -r .[].outputs.out)
-path1_stuff=$(echo $json | jq -r .[].outputs.stuff)
-[[ $(< $path1/n) = 0 ]]
-[[ $(< $path1_stuff/bla) = 0 ]]
-
-[[ $(nix path-info --json $path1 | jq .[].ca) =~ fixed:r:sha256: ]]
-
-path2=$(nix build -L --no-link --json --file ./impure-derivations.nix impure | jq -r .[].outputs.out)
-[[ $(< $path2/n) = 1 ]]
-
-# Test impure derivations that depend on impure derivations.
-path3=$(nix build -L --no-link --json --file ./impure-derivations.nix impureOnImpure | jq -r .[].outputs.out)
-[[ $(< $path3/n) = X2 ]]
-
-path4=$(nix build -L --no-link --json --file ./impure-derivations.nix impureOnImpure | jq -r .[].outputs.out)
-[[ $(< $path4/n) = X3 ]]
-
-# Test that (self-)references work.
-[[ $(< $path4/symlink/bla) = 3 ]]
-[[ $(< $path4/self/n) = X3 ]]
-
-# Input-addressed derivations cannot depend on impure derivations directly.
-(! nix build -L --no-link --json --file ./impure-derivations.nix inputAddressed 2>&1) | grep 'depends on impure derivation'
-
-drvPath=$(nix eval --json --file ./impure-derivations.nix impure.drvPath | jq -r .)
-[[ $(nix derivation show $drvPath | jq ".[\"$drvPath\"].outputs.out.impure") = true ]]
-[[ $(nix derivation show $drvPath | jq ".[\"$drvPath\"].outputs.stuff.impure") = true ]]
-
-# Fixed-output derivations *can* depend on impure derivations.
-path5=$(nix build -L --no-link --json --file ./impure-derivations.nix contentAddressed | jq -r .[].outputs.out)
-[[ $(< $path5) = X ]]
-[[ $(< $TEST_ROOT/counter) = 5 ]]
-
-# And they should not be rebuilt.
-path5=$(nix build -L --no-link --json --file ./impure-derivations.nix contentAddressed | jq -r .[].outputs.out)
-[[ $(< $path5) = X ]]
-[[ $(< $TEST_ROOT/counter) = 5 ]]
-
-# Input-addressed derivations can depend on fixed-output derivations that depend on impure derivations.
-path6=$(nix build -L --no-link --json --file ./impure-derivations.nix inputAddressedAfterCA | jq -r .[].outputs.out)
-[[ $(< $path6) = X ]]
-[[ $(< $TEST_ROOT/counter) = 5 ]]
diff --git a/tests/functional/meson.build b/tests/functional/meson.build
index 2c3f843d3..621a4c134 100644
--- a/tests/functional/meson.build
+++ b/tests/functional/meson.build
@@ -186,7 +186,6 @@ functional_tests_scripts = [
   'fetchClosure.sh',
   'completions.sh',
   'flakes/show.sh',
-  'impure-derivations.sh',
   'path-from-hash-part.sh',
   'toString-path.sh',
   'read-only-store.sh',
diff --git a/tests/unit/libexpr/error_traces.cc b/tests/unit/libexpr/error_traces.cc
index 84c1b8733..f3163437c 100644
--- a/tests/unit/libexpr/error_traces.cc
+++ b/tests/unit/libexpr/error_traces.cc
@@ -1290,16 +1290,6 @@ namespace nix {
                       HintFmt("expected a Boolean but found %s: %s", "a string", "\"true\""),
                       HintFmt("while evaluating the attribute '__contentAddressed' of derivation 'foo'"));
 
-        ASSERT_TRACE2("derivationStrict { name = \"foo\"; builder = 1; system = 1; outputs = \"out\"; __impure = \"true\"; }",
-                      TypeError,
-                      HintFmt("expected a Boolean but found %s: %s", "a string", "\"true\""),
-                      HintFmt("while evaluating the attribute '__impure' of derivation 'foo'"));
-
-        ASSERT_TRACE2("derivationStrict { name = \"foo\"; builder = 1; system = 1; outputs = \"out\"; __impure = \"true\"; }",
-                      TypeError,
-                      HintFmt("expected a Boolean but found %s: %s", "a string", "\"true\""),
-                      HintFmt("while evaluating the attribute '__impure' of derivation 'foo'"));
-
         ASSERT_TRACE2("derivationStrict { name = \"foo\"; builder = 1; system = 1; outputs = \"out\"; args = \"foo\"; }",
                       TypeError,
                       HintFmt("expected a list but found %s: %s", "a string", "\"foo\""),
diff --git a/tests/unit/libstore/data/libstore/derivation/output-impure.json b/tests/unit/libstore/data/libstore/derivation/output-impure.json
deleted file mode 100644
index 62b61cdca..000000000
--- a/tests/unit/libstore/data/libstore/derivation/output-impure.json
+++ /dev/null
@@ -1,4 +0,0 @@
-{
-  "hashAlgo": "r:sha256",
-  "impure": true
-}
diff --git a/tests/unit/libstore/derivation.cc b/tests/unit/libstore/derivation.cc
index edcabef44..77a27f5e9 100644
--- a/tests/unit/libstore/derivation.cc
+++ b/tests/unit/libstore/derivation.cc
@@ -41,14 +41,6 @@ class DynDerivationTest : public DerivationTest
     }
 };
 
-class ImpureDerivationTest : public DerivationTest
-{
-    void SetUp() override
-    {
-        mockXpSettings.set("experimental-features", "impure-derivations");
-    }
-};
-
 TEST_F(DerivationTest, BadATerm_version) {
     ASSERT_THROW(
         parseDerivation(
@@ -154,13 +146,6 @@ TEST_JSON(DerivationTest, deferred,
     DerivationOutput::Deferred { },
     "drv-name", "output-name")
 
-TEST_JSON(ImpureDerivationTest, impure,
-    (DerivationOutput::Impure {
-        .method = FileIngestionMethod::Recursive,
-        .hashType = HashType::SHA256,
-    }),
-    "drv-name", "output-name")
-
 #undef TEST_JSON
 
 #define TEST_JSON(FIXTURE, NAME, VAL)                                     \