diff --git a/src/nix/diff-closures.cc b/src/nix/diff-closures.cc
new file mode 100644
index 000000000..df0b26ab1
--- /dev/null
+++ b/src/nix/diff-closures.cc
@@ -0,0 +1,134 @@
+#include "command.hh"
+#include "shared.hh"
+#include "store-api.hh"
+#include "common-args.hh"
+#include "names.hh"
+
+#include <regex>
+
+using namespace nix;
+
+struct Info
+{
+    std::string outputName;
+};
+
+// name -> version -> store paths
+typedef std::map<std::string, std::map<std::string, std::map<StorePath, Info>>> GroupedPaths;
+
+GroupedPaths getClosureInfo(ref<Store> store, const StorePath & toplevel)
+{
+    StorePathSet closure;
+    store->computeFSClosure({toplevel}, closure);
+
+    GroupedPaths groupedPaths;
+
+    for (auto & path : closure) {
+        /* Strip the output name. Unfortunately this is ambiguous (we
+           can't distinguish between output names like "bin" and
+           version suffixes like "unstable"). */
+        static std::regex regex("(.*)-([a-z]+|lib32|lib64)");
+        std::smatch match;
+        std::string name(path.name());
+        std::string outputName;
+        if (std::regex_match(name, match, regex)) {
+            name = match[1];
+            outputName = match[2];
+        }
+
+        DrvName drvName(name);
+        groupedPaths[drvName.name][drvName.version].emplace(path, Info { .outputName = outputName });
+    }
+
+    return groupedPaths;
+}
+
+std::string showVersions(const std::set<std::string> & versions)
+{
+    if (versions.empty()) return "∅";
+    std::set<std::string> versions2;
+    for (auto & version : versions)
+        versions2.insert(version.empty() ? "ε" : version);
+    return concatStringsSep(", ", versions2);
+}
+
+struct CmdDiffClosures : SourceExprCommand
+{
+    std::string _before, _after;
+
+    CmdDiffClosures()
+    {
+        expectArg("before", &_before);
+        expectArg("after", &_after);
+    }
+
+    std::string description() override
+    {
+        return "show what packages and versions were added and removed between two closures";
+    }
+
+    Category category() override { return catSecondary; }
+
+    Examples examples() override
+    {
+        return {
+            {
+                "To show what got added and removed between two versions of the NixOS system profile:",
+                "nix diff-closures /nix/var/nix/profiles/system-655-link /nix/var/nix/profiles/system-658-link",
+            },
+        };
+    }
+
+    void run(ref<Store> store) override
+    {
+        auto before = parseInstallable(*this, store, _before, false);
+        auto beforePath = toStorePath(store, Build, before);
+        auto after = parseInstallable(*this, store, _after, false);
+        auto afterPath = toStorePath(store, NoBuild, after);
+
+        auto beforeClosure = getClosureInfo(store, beforePath);
+        auto afterClosure = getClosureInfo(store, afterPath);
+
+        std::set<std::string> allNames;
+        for (auto & [name, _] : beforeClosure) allNames.insert(name);
+        for (auto & [name, _] : afterClosure) allNames.insert(name);
+
+        for (auto & name : allNames) {
+            auto & beforeVersions = beforeClosure[name];
+            auto & afterVersions = afterClosure[name];
+
+            auto totalSize = [&](const std::map<std::string, std::map<StorePath, Info>> & versions)
+            {
+                uint64_t sum = 0;
+                for (auto & [_, paths] : versions)
+                    for (auto & [path, _] : paths)
+                        sum += store->queryPathInfo(path)->narSize;
+                return sum;
+            };
+
+            auto beforeSize = totalSize(beforeVersions);
+            auto afterSize = totalSize(afterVersions);
+            auto sizeDelta = (int64_t) afterSize - (int64_t) beforeSize;
+            auto showDelta = abs(sizeDelta) >= 8 * 1024;
+
+            std::set<std::string> removed, unchanged;
+            for (auto & [version, _] : beforeVersions)
+                if (!afterVersions.count(version)) removed.insert(version); else unchanged.insert(version);
+
+            std::set<std::string> added;
+            for (auto & [version, _] : afterVersions)
+                if (!beforeVersions.count(version)) added.insert(version);
+
+            if (showDelta || !removed.empty() || !added.empty()) {
+                std::vector<std::string> items;
+                if (!removed.empty() || !added.empty())
+                    items.push_back(fmt("%s → %s", showVersions(removed), showVersions(added)));
+                if (showDelta)
+                    items.push_back(fmt("%s%+.1f KiB" ANSI_NORMAL, sizeDelta > 0 ? ANSI_RED : ANSI_GREEN, sizeDelta / 1024.0));
+                std::cout << fmt("%s: %s\n", name, concatStringsSep(", ", items));
+            }
+        }
+    }
+};
+
+static auto r1 = registerCommand<CmdDiffClosures>("diff-closures");