diff --git a/doc/manual/rl-next/deprecated-derivation-types.md b/doc/manual/rl-next/deprecated-derivation-types.md
new file mode 100644
index 000000000..011c9e2bc
--- /dev/null
+++ b/doc/manual/rl-next/deprecated-derivation-types.md
@@ -0,0 +1,16 @@
+---
+synopsis: Deprecation of CA derivations, dynamic derivations, and impure derivations
+issues: [fj#815]
+cls: []
+significance: significant
+category: Miscellany
+credits: []
+---
+
+Content-addressed derivations are now deprecated and slated for removal in Lix 2.94.
+We're doing this because the CA derivation system has been a known cause of problems
+and inconsistencies, is unmaintained, habitually makes improving the store code very
+difficult (or blocks such improvements outright), and is beset by a number of design
+flaws that in our opinion cannot be fixed without a full reimplementation from zero.
+Dynamic derivations and impure derivations are built on the CA derivation framework,
+and owing to this they too are deprecated and slated for removal in another release.
diff --git a/lix/libutil/config.cc b/lix/libutil/config.cc
index 55ecdcaf7..713b1b964 100644
--- a/lix/libutil/config.cc
+++ b/lix/libutil/config.cc
@@ -10,6 +10,7 @@
 #include "lix/libutil/strings.hh"
 
 #include "lix/libutil/config-impl.hh"
+#include <mutex>
 
 namespace nix {
 
@@ -343,11 +344,31 @@ template<> std::string BaseSetting<StringSet>::to_string() const
 
 template<> ExperimentalFeatures BaseSetting<ExperimentalFeatures>::parse(const std::string & str, const ApplyConfigOptions & options) const
 {
+    auto warnDeprecated294 = [](std::once_flag & flag, std::string_view thing) {
+        std::call_once(flag, [&] {
+            warn(
+                "The %s experimental feature is deprecated and will be removed in Lix 2.94. "
+                "See https://git.lix.systems/lix-project/lix/issues/815 for more details.",
+                thing
+            );
+        });
+    };
+
     ExperimentalFeatures res{};
     for (auto & s : tokenizeString<StringSet>(str)) {
-        if (auto thisXpFeature = parseExperimentalFeature(s); thisXpFeature)
+        if (auto thisXpFeature = parseExperimentalFeature(s); thisXpFeature) {
+            if (*thisXpFeature == Xp::CaDerivations) {
+                static std::once_flag warned;
+                warnDeprecated294(warned, s);
+            } else if (*thisXpFeature == Xp::DynamicDerivations) {
+                static std::once_flag warned;
+                warnDeprecated294(warned, s);
+            } else if (*thisXpFeature == Xp::ImpureDerivations) {
+                static std::once_flag warned;
+                warnDeprecated294(warned, s);
+            }
             res = res | thisXpFeature.value();
-        else
+        } else
             warn("unknown experimental feature '%s'", s);
     }
     return res;