diff --git a/Makefile b/Makefile
index 31b54b93d20..42c1ffcd396 100644
--- a/Makefile
+++ b/Makefile
@@ -29,6 +29,7 @@ makefiles += \
   tests/local.mk \
   tests/ca/local.mk \
   tests/dyn-drv/local.mk \
+  tests/git-hashing/local.mk \
   tests/test-libstoreconsumer/local.mk \
   tests/plugins/local.mk
 else
diff --git a/src/libexpr/primops.cc b/src/libexpr/primops.cc
index cd9a05bb29d..4212a717a96 100644
--- a/src/libexpr/primops.cc
+++ b/src/libexpr/primops.cc
@@ -1111,7 +1111,10 @@ drvName, Bindings * attrs, Value & v)
         auto handleHashMode = [&](const std::string_view s) {
             if (s == "recursive") ingestionMethod = FileIngestionMethod::Recursive;
             else if (s == "flat") ingestionMethod = FileIngestionMethod::Flat;
-            else if (s == "text") {
+            else if (s == "flat") {
+                experimentalFeatureSettings.require(Xp::GitHashing);
+                ingestionMethod = FileIngestionMethod::Flat;
+            } else if (s == "text") {
                 experimentalFeatureSettings.require(Xp::DynamicDerivations);
                 ingestionMethod = TextIngestionMethod {};
             } else
diff --git a/src/libexpr/primops/fetchTree.cc b/src/libexpr/primops/fetchTree.cc
index f040a35109a..93656ca043e 100644
--- a/src/libexpr/primops/fetchTree.cc
+++ b/src/libexpr/primops/fetchTree.cc
@@ -30,9 +30,13 @@ void emitTreeAttrs(
 
     // FIXME: support arbitrary input attributes.
 
-    auto narHash = input.getNarHash();
-    assert(narHash);
-    attrs.alloc("narHash").mkString(narHash->to_string(SRI, true));
+    if (auto narHash = input.getNarHash()) {
+        attrs.alloc("narHash").mkString(narHash->to_string(SRI, true));
+    } else if (auto treeHash = input.getTreeHash()) {
+        attrs.alloc("treeHash").mkString(treeHash->to_string(SRI, true));
+    } else
+        /* Must have either tree hash or NAR hash */
+        assert(false);
 
     if (input.getType() == "git")
         attrs.alloc("submodules").mkBool(
@@ -50,6 +54,11 @@ void emitTreeAttrs(
             attrs.alloc("shortRev").mkString(emptyHash.gitShortRev());
         }
 
+        if (auto treeHash = input.getTreeHash()) {
+            attrs.alloc("treeHash").mkString(treeHash->gitRev());
+            attrs.alloc("shortTreeHash").mkString(treeHash->gitRev());
+        }
+
         if (auto revCount = input.getRevCount())
             attrs.alloc("revCount").mkInt(*revCount);
         else if (emptyRevFallback)
diff --git a/src/libfetchers/fetchers.cc b/src/libfetchers/fetchers.cc
index e683b9f804a..a3963640d83 100644
--- a/src/libfetchers/fetchers.cc
+++ b/src/libfetchers/fetchers.cc
@@ -25,6 +25,8 @@ static void fixupInput(Input & input)
     input.getRef();
     if (input.getRev())
         input.locked = true;
+    if (input.getTreeHash())
+        input.locked = true;
     input.getRevCount();
     input.getLastModified();
     if (input.getNarHash())
@@ -89,7 +91,7 @@ Attrs Input::toAttrs() const
 
 bool Input::hasAllInfo() const
 {
-    return getNarHash() && scheme && scheme->hasAllInfo(*this);
+    return scheme && scheme->hasAllInfo(*this);
 }
 
 bool Input::operator ==(const Input & other) const
@@ -213,14 +215,19 @@ std::string Input::getName() const
 
 StorePath Input::computeStorePath(Store & store) const
 {
-    auto narHash = getNarHash();
-    if (!narHash)
-        throw Error("cannot compute store path for unlocked input '%s'", to_string());
-    return store.makeFixedOutputPath(getName(), FixedOutputInfo {
-        .method = FileIngestionMethod::Recursive,
-        .hash = *narHash,
-        .references = {},
-    });
+    if (auto treeHash = getTreeHash())
+        return store.makeFixedOutputPath(getName(), FixedOutputInfo {
+            .method = FileIngestionMethod::Git,
+            .hash = *treeHash,
+            .references = {},
+        });
+    if (auto narHash = getNarHash())
+        return store.makeFixedOutputPath(getName(), FixedOutputInfo {
+            .method = FileIngestionMethod::Recursive,
+            .hash = *narHash,
+            .references = {},
+        });
+    throw Error("cannot compute store path for unlocked input '%s'", to_string());
 }
 
 std::string Input::getType() const
@@ -262,6 +269,15 @@ std::optional<Hash> Input::getRev() const
     return hash;
 }
 
+std::optional<Hash> Input::getTreeHash() const
+{
+    if (auto s = maybeGetStrAttr(attrs, "treeHash")) {
+        experimentalFeatureSettings.require(Xp::GitHashing);
+        return Hash::parseAny(*s, htSHA1);
+    }
+    return {};
+}
+
 std::optional<uint64_t> Input::getRevCount() const
 {
     if (auto n = maybeGetIntAttr(attrs, "revCount"))
diff --git a/src/libfetchers/fetchers.hh b/src/libfetchers/fetchers.hh
index 6e10e95134f..e7af5f9a8d1 100644
--- a/src/libfetchers/fetchers.hh
+++ b/src/libfetchers/fetchers.hh
@@ -110,6 +110,7 @@ public:
     std::optional<Hash> getNarHash() const;
     std::optional<std::string> getRef() const;
     std::optional<Hash> getRev() const;
+    std::optional<Hash> getTreeHash() const;
     std::optional<uint64_t> getRevCount() const;
     std::optional<time_t> getLastModified() const;
 };
diff --git a/src/libfetchers/git.cc b/src/libfetchers/git.cc
index f8d89ab2fcd..5036bf511e7 100644
--- a/src/libfetchers/git.cc
+++ b/src/libfetchers/git.cc
@@ -3,6 +3,7 @@
 #include "globals.hh"
 #include "tarfile.hh"
 #include "store-api.hh"
+#include "git.hh"
 #include "url-parts.hh"
 #include "pathlocks.hh"
 #include "util.hh"
@@ -200,7 +201,7 @@ WorkdirInfo getWorkdirInfo(const Input & input, const Path & workdir)
     return WorkdirInfo { .clean = clean, .hasHead = hasHead };
 }
 
-std::pair<StorePath, Input> fetchFromWorkdir(ref<Store> store, Input & input, const Path & workdir, const WorkdirInfo & workdirInfo)
+std::pair<StorePath, Input> fetchFromWorkdir(ref<Store> store, Input & input, const Path & workdir, const WorkdirInfo & workdirInfo, FileIngestionMethod ingestionMethod)
 {
     const bool submodules = maybeGetBoolAttr(input.attrs, "submodules").value_or(false);
     auto gitDir = ".git";
@@ -272,7 +273,7 @@ struct GitInputScheme : InputScheme
         attrs.emplace("type", "git");
 
         for (auto & [name, value] : url.query) {
-            if (name == "rev" || name == "ref")
+            if (name == "rev" || name == "ref" || name == "treeHash" || name == "gitIngestion")
                 attrs.emplace(name, value);
             else if (name == "shallow" || name == "submodules" || name == "allRefs")
                 attrs.emplace(name, Explicit<bool> { value == "1" });
@@ -290,7 +291,7 @@ struct GitInputScheme : InputScheme
         if (maybeGetStrAttr(attrs, "type") != "git") return {};
 
         for (auto & [name, value] : attrs)
-            if (name != "type" && name != "url" && name != "ref" && name != "rev" && name != "shallow" && name != "submodules" && name != "lastModified" && name != "revCount" && name != "narHash" && name != "allRefs" && name != "name" && name != "dirtyRev" && name != "dirtyShortRev")
+            if (name != "type" && name != "url" && name != "ref" && name != "rev" && name != "shallow" && name != "submodules" && name != "gitIngestion" && name != "treeHash"  && name != "lastModified" && name != "revCount" && name != "narHash" && name != "allRefs" && name != "name" && name != "dirtyRev" && name != "dirtyShortRev")
                 throw Error("unsupported Git input attribute '%s'", name);
 
         parseURL(getStrAttr(attrs, "url"));
@@ -313,6 +314,9 @@ struct GitInputScheme : InputScheme
         auto url = parseURL(getStrAttr(input.attrs, "url"));
         if (url.scheme != "git") url.scheme = "git+" + url.scheme;
         if (auto rev = input.getRev()) url.query.insert_or_assign("rev", rev->gitRev());
+        if (auto treeHash = input.getTreeHash()) url.query.insert_or_assign("treeHash", treeHash->gitRev());
+        if (maybeGetBoolAttr(input.attrs, "gitIngestion").value_or((bool) input.getTreeHash()))
+            url.query.insert_or_assign("gitIngestion", "1");
         if (auto ref = input.getRef()) url.query.insert_or_assign("ref", *ref);
         if (maybeGetBoolAttr(input.attrs, "shallow").value_or(false))
             url.query.insert_or_assign("shallow", "1");
@@ -323,11 +327,18 @@ struct GitInputScheme : InputScheme
     {
         bool maybeDirty = !input.getRef();
         bool shallow = maybeGetBoolAttr(input.attrs, "shallow").value_or(false);
-        return
+        bool submodules = maybeGetBoolAttr(input.attrs, "submodules").value_or(false);
+        /* FIXME just requiring tree hash is necessary for substitutions to
+           work for now, but breaks eval purity. Need a better solution before
+           upstreaming. */
+        return (input.getTreeHash() && !submodules) || (
             maybeGetIntAttr(input.attrs, "lastModified")
-            && (shallow || maybeDirty || maybeGetIntAttr(input.attrs, "revCount"));
+            && (shallow || maybeDirty || maybeGetIntAttr(input.attrs, "revCount"))
+            && input.getNarHash());
     }
 
+    /* FIXME no overriding the tree hash / flake registry support for tree
+       hashes, for now. */
     Input applyOverrides(
         const Input & input,
         std::optional<std::string> ref,
@@ -364,7 +375,7 @@ struct GitInputScheme : InputScheme
     std::optional<Path> getSourcePath(const Input & input) override
     {
         auto url = parseURL(getStrAttr(input.attrs, "url"));
-        if (url.scheme == "file" && !input.getRef() && !input.getRev())
+        if (url.scheme == "file" && !input.getRef() && !input.getRev() && !input.getTreeHash())
             return url.path;
         return {};
     }
@@ -412,6 +423,11 @@ struct GitInputScheme : InputScheme
         if (submodules) cacheType += "-submodules";
         if (allRefs) cacheType += "-all-refs";
 
+        auto ingestionMethod =
+            maybeGetBoolAttr(input.attrs, "gitIngestion").value_or((bool) input.getTreeHash())
+            ? FileIngestionMethod::Git
+            : FileIngestionMethod::Recursive;
+
         auto checkHashType = [&](const std::optional<Hash> & hash)
         {
             if (hash.has_value() && !(hash->type == htSHA1 || hash->type == htSHA256))
@@ -420,20 +436,32 @@ struct GitInputScheme : InputScheme
 
         auto getLockedAttrs = [&]()
         {
-            checkHashType(input.getRev());
-
-            return Attrs({
+            Attrs attrs({
                 {"type", cacheType},
                 {"name", name},
-                {"rev", input.getRev()->gitRev()},
             });
+            if (auto optH = input.getTreeHash()) {
+                auto h = *std::move(optH);
+                checkHashType(h);
+                attrs.insert_or_assign("treeHash", h.gitRev());
+            }
+            if (auto optH = input.getRev()) {
+                auto h = *std::move(optH);
+                checkHashType(h);
+                attrs.insert_or_assign("rev", h.gitRev());
+            }
+            if (maybeGetBoolAttr(input.attrs, "gitIngestion").value_or((bool) input.getTreeHash()))
+                attrs.insert_or_assign("gitIngestion", true);
+            return attrs;
         };
 
         auto makeResult = [&](const Attrs & infoAttrs, StorePath && storePath)
             -> std::pair<StorePath, Input>
         {
-            assert(input.getRev());
+            assert(input.getRev() || input.getTreeHash());
+            /* If was originally set, that original value must be preserved. */
             assert(!_input.getRev() || _input.getRev() == input.getRev());
+            assert(!_input.getTreeHash() || _input.getTreeHash() == input.getTreeHash());
             if (!shallow)
                 input.attrs.insert_or_assign("revCount", getIntAttr(infoAttrs, "revCount"));
             input.attrs.insert_or_assign("lastModified", getIntAttr(infoAttrs, "lastModified"));
@@ -450,10 +478,10 @@ struct GitInputScheme : InputScheme
 
         /* If this is a local directory and no ref or revision is given,
            allow fetching directly from a dirty workdir. */
-        if (!input.getRef() && !input.getRev() && isLocal) {
+        if (!input.getRef() && !input.getRev() && !input.getTreeHash() && isLocal) {
             auto workdirInfo = getWorkdirInfo(input, actualUrl);
             if (!workdirInfo.clean) {
-                return fetchFromWorkdir(store, input, actualUrl, workdirInfo);
+                return fetchFromWorkdir(store, input, actualUrl, workdirInfo, ingestionMethod);
             }
         }
 
@@ -462,6 +490,8 @@ struct GitInputScheme : InputScheme
             {"name", name},
             {"url", actualUrl},
         });
+        if (ingestionMethod == FileIngestionMethod::Git)
+            unlockedAttrs.insert_or_assign("gitIngestion", true);
 
         Path repoDir;
 
@@ -476,9 +506,14 @@ struct GitInputScheme : InputScheme
                 unlockedAttrs.insert_or_assign("ref", *head);
             }
 
-            if (!input.getRev())
-                input.attrs.insert_or_assign("rev",
-                    Hash::parseAny(chomp(runProgram("git", true, { "-C", actualUrl, "--git-dir", gitDir, "rev-parse", *input.getRef() })), htSHA1).gitRev());
+            if (!input.getRev() && !input.getTreeHash()) {
+                auto getHash = [&](std::string rev) {
+                    return Hash::parseAny(chomp(runProgram("git", true, { "-C", actualUrl, "--git-dir", gitDir, "rev-parse", rev })), htSHA1).gitRev();
+                };
+                input.attrs.insert_or_assign("rev", getHash(*input.getRef()));
+                if (experimentalFeatureSettings.isEnabled(Xp::GitHashing))
+                    input.attrs.insert_or_assign("treeHash", getHash(*input.getRef() + ":"));
+            }
 
             repoDir = actualUrl;
         } else {
@@ -498,11 +533,33 @@ struct GitInputScheme : InputScheme
             }
 
             if (auto res = getCache()->lookup(store, unlockedAttrs)) {
-                auto rev2 = Hash::parseAny(getStrAttr(res->first, "rev"), htSHA1);
-                if (!input.getRev() || input.getRev() == rev2) {
-                    input.attrs.insert_or_assign("rev", rev2.gitRev());
-                    return makeResult(res->first, std::move(res->second));
+                bool found = false;
+
+                if (std::optional revS = maybeGetStrAttr(res->first, "rev")) {
+                    auto rev2 = Hash::parseAny(*revS, htSHA1);
+                    if (!input.getRev() || input.getRev() == rev2) {
+                        input.attrs.insert_or_assign("rev", rev2.gitRev());
+                        found = true;
+                    }
                 }
+
+                if (experimentalFeatureSettings.isEnabled(Xp::GitHashing)) {
+                    if (std::optional treeHashS = maybeGetStrAttr(res->first, "treeHash")) {
+                        auto treeHash2 = Hash::parseNonSRIUnprefixed(*treeHashS, htSHA1);
+                        if (!input.getTreeHash() || input.getTreeHash() == treeHash2) {
+                            input.attrs.insert_or_assign("treeHash", treeHash2.gitRev());
+                            found = true;
+                        }
+                    }
+                }
+
+                bool correctIngestion =
+                    maybeGetBoolAttr(input.attrs, "gitIngestion").value_or(false)
+                    ? ingestionMethod == FileIngestionMethod::Git
+                    : ingestionMethod == FileIngestionMethod::Recursive;
+
+                if (correctIngestion && found)
+                    return makeResult(res->first, std::move(res->second));
             }
 
             Path cacheDir = getCachePath(actualUrl);
@@ -524,11 +581,12 @@ struct GitInputScheme : InputScheme
             bool doFetch;
             time_t now = time(0);
 
-            /* If a rev was specified, we need to fetch if it's not in the
-               repo. */
-            if (input.getRev()) {
+            /* If a rev or treeHash is specified, we need to fetch if
+               it's not in the repo. */
+            if (input.getRev() || input.getTreeHash()) {
                 try {
-                    runProgram("git", true, { "-C", repoDir, "--git-dir", gitDir, "cat-file", "-e", input.getRev()->gitRev() });
+                    auto fetchHash = input.getTreeHash() ? input.getTreeHash() : input.getRev();
+                    runProgram("git", true, { "-C", repoDir, "--git-dir", gitDir, "cat-file", "-e", fetchHash->gitRev() });
                     doFetch = false;
                 } catch (ExecError & e) {
                     if (WIFEXITED(e.status)) {
@@ -575,12 +633,23 @@ struct GitInputScheme : InputScheme
                     warn("could not update cached head '%s' for '%s'", *input.getRef(), actualUrl);
             }
 
-            if (!input.getRev())
-                input.attrs.insert_or_assign("rev", Hash::parseAny(chomp(readFile(localRefFile)), htSHA1).gitRev());
+            if (!input.getRev() && !input.getTreeHash()) {
+                auto rev = Hash::parseAny(chomp(readFile(localRefFile)), htSHA1).gitRev();
+                input.attrs.insert_or_assign("rev", rev);
+                if (experimentalFeatureSettings.isEnabled(Xp::GitHashing))
+                    input.attrs.insert_or_assign("treeHash",
+                        Hash::parseAny(chomp(runProgram("git", true, { "-C", repoDir, "rev-parse", rev + ":" })), htSHA1).gitRev());
+            }
 
             // cache dir lock is removed at scope end; we will only use read-only operations on specific revisions in the remainder
         }
 
+        if (input.getTreeHash()) {
+            auto type = chomp(runProgram("git", true, { "-C", repoDir, "--git-dir", gitDir, "cat-file", "-t", input.getTreeHash()->gitRev() }));
+            if (type != "tree")
+                throw Error("Need a tree object, found '%s' object in %s", type, input.getTreeHash()->gitRev());
+        }
+
         bool isShallow = chomp(runProgram("git", true, { "-C", repoDir, "--git-dir", gitDir, "rev-parse", "--is-shallow-repository" })) == "true";
 
         if (isShallow && !shallow)
@@ -588,7 +657,10 @@ struct GitInputScheme : InputScheme
 
         // FIXME: check whether rev is an ancestor of ref.
 
-        printTalkative("using revision %s of repo '%s'", input.getRev()->gitRev(), actualUrl);
+        if (auto rev = input.getRev())
+            printTalkative("using revision %s of repo '%s'", rev->gitRev(), actualUrl);
+        if (auto treeHash = input.getTreeHash())
+            printTalkative("using tree %s of repo '%s'", treeHash->gitRev(), actualUrl);
 
         /* Now that we know the ref, check again whether we have it in
            the store. */
@@ -599,10 +671,20 @@ struct GitInputScheme : InputScheme
         AutoDelete delTmpDir(tmpDir, true);
         PathFilter filter = defaultPathFilter;
 
+        auto [fetchHash, fetchHashType] = input.getTreeHash()
+            ? (std::pair { input.getTreeHash().value(), true })
+            : (std::pair { input.getRev().value(), false });
+
         auto result = runProgram(RunOptions {
             .program = "git",
-            .args = { "-C", repoDir, "--git-dir", gitDir, "cat-file", "commit", input.getRev()->gitRev() },
-            .mergeStderrToStdout = true
+            .args = {
+                "-C", repoDir,
+                "--git-dir", gitDir,
+                "cat-file",
+                fetchHashType ? "tree" : "commit",
+                fetchHash.gitRev(),
+            },
+            .mergeStderrToStdout = true,
         });
         if (WEXITSTATUS(result.first) == 128
             && result.second.find("bad file") != std::string::npos)
@@ -612,13 +694,18 @@ struct GitInputScheme : InputScheme
                 "Please make sure that the " ANSI_BOLD "rev" ANSI_NORMAL " exists on the "
                 ANSI_BOLD "ref" ANSI_NORMAL " you've specified or add " ANSI_BOLD
                 "allRefs = true;" ANSI_NORMAL " to " ANSI_BOLD "fetchGit" ANSI_NORMAL ".",
-                input.getRev()->gitRev(),
+                fetchHash.gitRev(),
                 *input.getRef(),
                 actualUrl
             );
         }
 
         if (submodules) {
+            if (input.getTreeHash())
+                throw Error("Cannot fetch specific tree hashes if there are submodules");
+            if (ingestionMethod == FileIngestionMethod::Git)
+                warn("Nix's computed git tree hash will be different when submodules are converted to regular directories");
+
             Path tmpGitDir = createTempDir();
             AutoDelete delTmpGitDir(tmpGitDir, true);
 
@@ -633,7 +720,7 @@ struct GitInputScheme : InputScheme
                         "--update-head-ok", "--", repoDir, "refs/*:refs/*" }, {}, true);
             }
 
-            runProgram("git", true, { "-C", tmpDir, "checkout", "--quiet", input.getRev()->gitRev() });
+            runProgram("git", true, { "-C", tmpDir, "checkout", "--quiet", input.getTreeHash() ? input.getTreeHash()->gitRev() : input.getRev()->gitRev() });
 
             /* Ensure that we use the correct origin for fetching
                submodules. This matters for submodules with relative
@@ -662,12 +749,13 @@ struct GitInputScheme : InputScheme
 
             filter = isNotDotGitDirectory;
         } else {
+            auto & fetchHash_ = fetchHash; // Work-around clang restriction.
             // FIXME: should pipe this, or find some better way to extract a
             // revision.
             auto source = sinkToSource([&](Sink & sink) {
                 runProgram2({
                     .program = "git",
-                    .args = { "-C", repoDir, "--git-dir", gitDir, "archive", input.getRev()->gitRev() },
+                    .args = { "-C", repoDir, "--git-dir", gitDir, "archive", fetchHash_.gitRev() },
                     .standardOut = &sink
                 });
             });
@@ -675,20 +763,39 @@ struct GitInputScheme : InputScheme
             unpackTarfile(*source, tmpDir);
         }
 
-        auto storePath = store->addToStore(name, tmpDir, FileIngestionMethod::Recursive, htSHA256, filter);
+        auto storePath = store->addToStore(name, tmpDir, ingestionMethod, ingestionMethod == FileIngestionMethod::Git ? htSHA1 : htSHA256, filter);
 
-        auto lastModified = std::stoull(runProgram("git", true, { "-C", repoDir, "--git-dir", gitDir, "log", "-1", "--format=%ct", "--no-show-signature", input.getRev()->gitRev() }));
+        // verify treeHash is what we actually obtained in the nix store
+        if (auto treeHash = input.getTreeHash()) {
+            auto path = store->toRealPath(store->printStorePath(storePath));
+            auto gotHash = dumpGitHash(htSHA1, path);
+            if (gotHash != input.getTreeHash())
+                throw Error("Git hash mismatch in input '%s' (%s), expected '%s', got '%s'",
+                    input.to_string(), path, treeHash->gitRev(), gotHash.gitRev());
+        }
 
-        Attrs infoAttrs({
-            {"rev", input.getRev()->gitRev()},
-            {"lastModified", lastModified},
-        });
+        Attrs infoAttrs({});
+
+        if (auto rev = input.getRev()) {
+            infoAttrs.insert_or_assign("rev", rev->gitRev());
+            auto lastModified = std::stoull(runProgram("git", true, { "-C", repoDir, "--git-dir", gitDir, "log", "-1", "--format=%ct", "--no-show-signature", rev->gitRev() }));
+            infoAttrs.insert_or_assign("lastModified", lastModified);
+        } else
+            infoAttrs.insert_or_assign("lastModified", (uint64_t) 0);
 
-        if (!shallow)
-            infoAttrs.insert_or_assign("revCount",
-                std::stoull(runProgram("git", true, { "-C", repoDir, "--git-dir", gitDir, "rev-list", "--count", input.getRev()->gitRev() })));
+        if (experimentalFeatureSettings.isEnabled(Xp::GitHashing))
+            if (auto treeHash = input.getTreeHash())
+                infoAttrs.insert_or_assign("treeHash", treeHash->gitRev());
+
+        if (!shallow) {
+            if (auto rev = input.getRev())
+                infoAttrs.insert_or_assign("revCount",
+                    std::stoull(runProgram("git", true, { "-C", repoDir, "--git-dir", gitDir, "rev-list", "--count", rev->gitRev() })));
+            else
+                infoAttrs.insert_or_assign("revCount", (uint64_t) 0);
+        }
 
-        if (!_input.getRev())
+        if (!_input.getRev() && !_input.getTreeHash())
             getCache()->add(
                 store,
                 unlockedAttrs,
diff --git a/src/libfetchers/github.cc b/src/libfetchers/github.cc
index 291f457f0d3..4fa4f3e07b2 100644
--- a/src/libfetchers/github.cc
+++ b/src/libfetchers/github.cc
@@ -134,7 +134,7 @@ struct GitArchiveInputScheme : InputScheme
 
     bool hasAllInfo(const Input & input) const override
     {
-        return input.getRev() && maybeGetIntAttr(input.attrs, "lastModified");
+        return input.getNarHash() && input.getRev() && maybeGetIntAttr(input.attrs, "lastModified");
     }
 
     Input applyOverrides(
diff --git a/src/libfetchers/mercurial.cc b/src/libfetchers/mercurial.cc
index 51fd1ed428b..74cb9c36380 100644
--- a/src/libfetchers/mercurial.cc
+++ b/src/libfetchers/mercurial.cc
@@ -102,7 +102,8 @@ struct MercurialInputScheme : InputScheme
     {
         // FIXME: ugly, need to distinguish between dirty and clean
         // default trees.
-        return input.getRef() == "default" || maybeGetIntAttr(input.attrs, "revCount");
+        return input.getNarHash()
+            && (input.getRef() == "default" || maybeGetIntAttr(input.attrs, "revCount"));
     }
 
     Input applyOverrides(
diff --git a/src/libfetchers/path.cc b/src/libfetchers/path.cc
index 01f1be97822..10670bb4ac5 100644
--- a/src/libfetchers/path.cc
+++ b/src/libfetchers/path.cc
@@ -68,7 +68,7 @@ struct PathInputScheme : InputScheme
 
     bool hasAllInfo(const Input & input) const override
     {
-        return true;
+        return (bool) input.getNarHash();
     }
 
     std::optional<Path> getSourcePath(const Input & input) override
diff --git a/src/libstore/binary-cache-store.cc b/src/libstore/binary-cache-store.cc
index b4fea693f5b..df7f63fbd9f 100644
--- a/src/libstore/binary-cache-store.cc
+++ b/src/libstore/binary-cache-store.cc
@@ -411,10 +411,15 @@ StorePath BinaryCacheStore::addToStore(
        implementation of this method in terms of addToStoreFromDump. */
 
     HashSink sink { hashAlgo };
-    if (method == FileIngestionMethod::Recursive) {
+    switch (method) {
+    case FileIngestionMethod::Recursive:
         dumpPath(srcPath, sink, filter);
-    } else {
+        break;
+    case FileIngestionMethod::Flat:
         readFile(srcPath, sink);
+        break;
+    case FileIngestionMethod::Git:
+        throw Error("cannot add to binary cache store using the git file ingestion method");
     }
     auto h = sink.finish().first;
 
diff --git a/src/libstore/build/local-derivation-goal.cc b/src/libstore/build/local-derivation-goal.cc
index 64b55ca6ac2..9883321efeb 100644
--- a/src/libstore/build/local-derivation-goal.cc
+++ b/src/libstore/build/local-derivation-goal.cc
@@ -8,6 +8,7 @@
 #include "finally.hh"
 #include "util.hh"
 #include "archive.hh"
+#include "git.hh"
 #include "compression.hh"
 #include "daemon.hh"
 #include "topo-sort.hh"
@@ -2480,23 +2481,34 @@ SingleDrvOutputs LocalDerivationGoal::registerOutputs()
             rewriteOutput(outputRewrites);
             /* FIXME optimize and deduplicate with addToStore */
             std::string oldHashPart { scratchPath->hashPart() };
-            HashModuloSink caSink { outputHash.hashType, oldHashPart };
+            Hash got { outputHash.hashType }; // Dummy value
             std::visit(overloaded {
                 [&](const TextIngestionMethod &) {
+                    HashModuloSink caSink { outputHash.hashType, oldHashPart };
                     readFile(actualPath, caSink);
+                    got = caSink.finish().first;
                 },
                 [&](const FileIngestionMethod & m2) {
                     switch (m2) {
-                    case FileIngestionMethod::Recursive:
+                    case FileIngestionMethod::Recursive: {
+                        HashModuloSink caSink { outputHash.hashType, oldHashPart };
                         dumpPath(actualPath, caSink);
+                        got = caSink.finish().first;
                         break;
-                    case FileIngestionMethod::Flat:
+                    }
+                    case FileIngestionMethod::Flat: {
+                        HashModuloSink caSink { outputHash.hashType, oldHashPart };
                         readFile(actualPath, caSink);
+                        got = caSink.finish().first;
+                        break;
+                    }
+                    case FileIngestionMethod::Git: {
+                        got = dumpGitHash(outputHash.hashType, (Path) tmpDir + "/tmp");
                         break;
                     }
+                    }
                 },
             }, outputHash.method.raw);
-            auto got = caSink.finish().first;
 
             auto optCA = ContentAddressWithReferences::fromPartsOpt(
                 outputHash.method,
diff --git a/src/libstore/content-address.cc b/src/libstore/content-address.cc
index e290a8d387e..d7f4267d75f 100644
--- a/src/libstore/content-address.cc
+++ b/src/libstore/content-address.cc
@@ -11,6 +11,9 @@ std::string makeFileIngestionPrefix(FileIngestionMethod m)
         return "";
     case FileIngestionMethod::Recursive:
         return "r:";
+    case FileIngestionMethod::Git:
+        experimentalFeatureSettings.require(Xp::GitHashing);
+        return "git:";
     default:
         throw Error("impossible, caught both cases");
     }
@@ -32,6 +35,10 @@ ContentAddressMethod ContentAddressMethod::parsePrefix(std::string_view & m)
     ContentAddressMethod method = FileIngestionMethod::Flat;
     if (splitPrefix(m, "r:"))
         method = FileIngestionMethod::Recursive;
+    if (splitPrefix(m, "git:")) {
+        experimentalFeatureSettings.require(Xp::GitHashing);
+        method = FileIngestionMethod::Git;
+    }
     else if (splitPrefix(m, "text:"))
         method = TextIngestionMethod {};
     return method;
@@ -99,6 +106,10 @@ static std::pair<ContentAddressMethod, HashType> parseContentAddressMethodPrefix
         auto method = FileIngestionMethod::Flat;
         if (splitPrefix(rest, "r:"))
             method = FileIngestionMethod::Recursive;
+        if (splitPrefix(rest, "git:")) {
+            experimentalFeatureSettings.require(Xp::GitHashing);
+            method = FileIngestionMethod::Git;
+        }
         HashType hashType = parseHashType_();
         return {
             std::move(method),
diff --git a/src/libstore/content-address.hh b/src/libstore/content-address.hh
index c4d619bdc63..5d92cd575f9 100644
--- a/src/libstore/content-address.hh
+++ b/src/libstore/content-address.hh
@@ -39,12 +39,26 @@ enum struct FileIngestionMethod : uint8_t {
     /**
      * Flat-file hashing. Directly ingest the contents of a single file
      */
-    Flat = false,
+    Flat,
+
     /**
      * Recursive (or NAR) hashing. Serializes the file-system object in Nix
      * Archive format and ingest that
      */
-    Recursive = true
+    Recursive,
+
+    /**
+     * Git hashing. In particular files are hashed as git "blobs", and
+     * directories are hashed as git "trees".
+     *
+     * @note Git's data model is slightly different, in that a plain
+     * fail doesn't have an executable bit, directory entries do
+     * instead. We decide treat a bare file as non-executable by fiat,
+     * as we do with `FileIngestionMethod::Flat` which also lacks this
+     * information. Thus, Git can encode some but all of Nix's "File
+     * System Objects", and this sort of hashing is likewise partial.
+     */
+    Git,
 };
 
 /**
diff --git a/src/libstore/daemon.cc b/src/libstore/daemon.cc
index 8cbf6f044fa..af6d6d69b68 100644
--- a/src/libstore/daemon.cc
+++ b/src/libstore/daemon.cc
@@ -13,6 +13,7 @@
 #include "archive.hh"
 #include "derivations.hh"
 #include "args.hh"
+#include "git.hh"
 
 namespace nix::daemon {
 
@@ -462,13 +463,17 @@ static void performOp(TunnelLogger * logger, ref<Store> store,
                     TeeSource savedNARSource(from, saved);
                     ParseSink sink; /* null sink; just parse the NAR */
                     parseDump(sink, savedNARSource);
-                } else {
+                } else if (method == FileIngestionMethod::Flat) {
                     /* Incrementally parse the NAR file, stripping the
                        metadata, and streaming the sole file we expect into
                        `saved`. */
                     RetrieveRegularNARSink savedRegular { saved };
                     parseDump(savedRegular, from);
                     if (!savedRegular.regular) throw Error("regular file expected");
+                } else {
+                    /* Should have validated above that no other file ingestion
+                       method was used. */
+                    assert(false);
                 }
             });
             logger->startWork();
diff --git a/src/libstore/local-store.cc b/src/libstore/local-store.cc
index 17b4ecc7312..659bcf213b9 100644
--- a/src/libstore/local-store.cc
+++ b/src/libstore/local-store.cc
@@ -1,5 +1,6 @@
 #include "local-store.hh"
 #include "globals.hh"
+#include "git.hh"
 #include "archive.hh"
 #include "pathlocks.hh"
 #include "worker-protocol.hh"
@@ -1322,10 +1323,22 @@ StorePath LocalStore::addToStoreFromDump(Source & source0, std::string_view name
         delTempDir = std::make_unique<AutoDelete>(tempDir);
         tempPath = tempDir + "/x";
 
-        if (method == FileIngestionMethod::Recursive)
-            restorePath(tempPath, bothSource);
-        else
+        switch (method) {
+        case FileIngestionMethod::Flat:
             writeFile(tempPath, bothSource);
+            break;
+        case FileIngestionMethod::Recursive:
+            restorePath(tempPath, bothSource);
+            break;
+        case FileIngestionMethod::Git:
+            restoreGit(tempPath, bothSource, [&](Hash childHash) {
+                return this->Store::toRealPath(this->makeFixedOutputPath("git", FixedOutputInfo {
+                    .method = FileIngestionMethod::Git,
+                    .hash = childHash,
+                }));
+            });
+            break;
+        }
 
         dump.clear();
     }
@@ -1364,10 +1377,22 @@ StorePath LocalStore::addToStoreFromDump(Source & source0, std::string_view name
             if (inMemory) {
                 StringSource dumpSource { dump };
                 /* Restore from the NAR in memory. */
-                if (method == FileIngestionMethod::Recursive)
-                    restorePath(realPath, dumpSource);
-                else
+                switch (method) {
+                case FileIngestionMethod::Flat:
                     writeFile(realPath, dumpSource);
+                    break;
+                case FileIngestionMethod::Recursive:
+                    restorePath(realPath, dumpSource);
+                    break;
+                case FileIngestionMethod::Git:
+                    restoreGit(realPath, dumpSource, [&](Hash childHash) {
+                        return this->Store::toRealPath(this->makeFixedOutputPath("git", FixedOutputInfo {
+                            .method = FileIngestionMethod::Git,
+                            .hash = childHash,
+                        }));
+                    });
+                    break;
+                }
             } else {
                 /* Move the temporary path we restored above. */
                 moveFile(tempPath, realPath);
@@ -1866,25 +1891,37 @@ ContentAddress LocalStore::hashCAPath(
     const std::string_view pathHash
 )
 {
-    HashModuloSink caSink ( hashType, std::string(pathHash) );
+    Hash hash { htSHA256 }; // throwaway def to appease C++
     std::visit(overloaded {
         [&](const TextIngestionMethod &) {
+            HashModuloSink caSink ( hashType, std::string(pathHash) );
             readFile(path, caSink);
+            hash = caSink.finish().first;
         },
         [&](const FileIngestionMethod & m2) {
             switch (m2) {
-            case FileIngestionMethod::Recursive:
+            case FileIngestionMethod::Recursive: {
+                HashModuloSink caSink ( hashType, std::string(pathHash) );
                 dumpPath(path, caSink);
+                hash = caSink.finish().first;
                 break;
-            case FileIngestionMethod::Flat:
+            }
+            case FileIngestionMethod::Flat: {
+                HashModuloSink caSink ( hashType, std::string(pathHash) );
                 readFile(path, caSink);
+                hash = caSink.finish().first;
                 break;
             }
+            case FileIngestionMethod::Git: {
+                hash = dumpGitHash(hashType, path);
+                break;
+            }
+            }
         },
     }, method.raw);
     return ContentAddress {
         .method = method,
-        .hash = caSink.finish().first,
+        .hash = std::move(hash),
     };
 }
 
diff --git a/src/libstore/nar-accessor.cc b/src/libstore/nar-accessor.cc
index f0dfcb19b77..3cdd6b64513 100644
--- a/src/libstore/nar-accessor.cc
+++ b/src/libstore/nar-accessor.cc
@@ -69,9 +69,10 @@ struct NarAccessor : public FSAccessor
             createMember(path, {FSAccessor::Type::tDirectory, false, 0, 0});
         }
 
-        void createRegularFile(const Path & path) override
+        void createRegularFile(const Path & path, bool executable = false) override
         {
             createMember(path, {FSAccessor::Type::tRegular, false, 0, 0});
+            if (executable) isExecutable();
         }
 
         void closeRegularFile() override
diff --git a/src/libstore/remote-store.cc b/src/libstore/remote-store.cc
index a639346d1ad..6f4cdb5e454 100644
--- a/src/libstore/remote-store.cc
+++ b/src/libstore/remote-store.cc
@@ -13,6 +13,7 @@
 #include "derivations.hh"
 #include "pool.hh"
 #include "finally.hh"
+#include "git.hh"
 #include "logging.hh"
 #include "callback.hh"
 #include "filetransfer.hh"
diff --git a/src/libstore/store-api.cc b/src/libstore/store-api.cc
index 28689e100e2..5ea2219bd71 100644
--- a/src/libstore/store-api.cc
+++ b/src/libstore/store-api.cc
@@ -10,6 +10,7 @@
 #include "references.hh"
 #include "archive.hh"
 #include "callback.hh"
+#include "git.hh"
 #include "remote-store.hh"
 
 #include <nlohmann/json.hpp>
@@ -114,8 +115,8 @@ StorePath Store::followLinksToStorePath(std::string_view path) const
        for paths copied by addToStore() or produced by fixed-output
        derivations:
          the string "fixed:out:<rec><algo>:<hash>:", where
-           <rec> = "r:" for recursive (path) hashes, or "" for flat
-             (file) hashes
+           <rec> = "r:" for recursive (path) hashes, "git:" for git
+             paths, or "" for flat (file) hashes
            <algo> = "md5", "sha1" or "sha256"
            <hash> = base-16 representation of the path or flat hash of
              the contents of the path (or expected contents of the
@@ -184,6 +185,9 @@ static std::string makeType(
 
 StorePath Store::makeFixedOutputPath(std::string_view name, const FixedOutputInfo & info) const
 {
+    if (info.method == FileIngestionMethod::Git && info.hash.type != htSHA1)
+        throw Error("Git file ingestion must use sha1 hash");
+
     if (info.hash.type == htSHA256 && info.method == FileIngestionMethod::Recursive) {
         return makeStorePath(makeType(*this, "source", info.references), info.hash, name);
     } else {
@@ -228,9 +232,22 @@ StorePath Store::makeFixedOutputPathFromCA(std::string_view name, const ContentA
 std::pair<StorePath, Hash> Store::computeStorePathForPath(std::string_view name,
     const Path & srcPath, FileIngestionMethod method, HashType hashAlgo, PathFilter & filter) const
 {
-    Hash h = method == FileIngestionMethod::Recursive
-        ? hashPath(hashAlgo, srcPath, filter).first
-        : hashFile(hashAlgo, srcPath);
+    Hash h { htSHA256 }; // throwaway def to appease C++
+    switch (method) {
+    case FileIngestionMethod::Recursive: {
+        h = hashPath(hashAlgo, srcPath, filter).first;
+        break;
+    }
+    case FileIngestionMethod::Git: {
+        h = hashGit(hashAlgo, srcPath, filter).first;
+        break;
+    }
+    case FileIngestionMethod::Flat: {
+        h = hashFile(hashAlgo, srcPath);
+        break;
+    }
+    }
+
     FixedOutputInfo caInfo {
         .method = method,
         .hash = h,
@@ -263,10 +280,29 @@ StorePath Store::addToStore(
 {
     Path srcPath(absPath(_srcPath));
     auto source = sinkToSource([&](Sink & sink) {
-        if (method == FileIngestionMethod::Recursive)
+        switch (method) {
+        case FileIngestionMethod::Recursive: {
             dumpPath(srcPath, sink, filter);
-        else
+            break;
+        }
+        case FileIngestionMethod::Git: {
+            // recursively add to store if path is a directory
+
+            struct stat st;
+            if (lstat(srcPath.c_str(), &st))
+                throw SysError("getting attributes of path '%1%'", srcPath);
+            if (S_ISDIR(st.st_mode))
+                for (auto & i : readDirectory(srcPath))
+                    addToStore("git", srcPath + "/" + i.name, method, hashAlgo, filter, repair);
+
+            dumpGit(hashAlgo, srcPath, sink, filter);
+            break;
+        }
+        case FileIngestionMethod::Flat: {
             readFile(srcPath, sink);
+            break;
+        }
+        }
     });
     return addToStoreFromDump(*source, name, method, hashAlgo, repair, references);
 }
@@ -430,6 +466,8 @@ ValidPathInfo Store::addToStoreSlow(std::string_view name, const Path & srcPath,
 
     auto hash = method == FileIngestionMethod::Recursive && hashAlgo == htSHA256
         ? narHash
+        : method == FileIngestionMethod::Git
+        ? hashGit(hashAlgo, srcPath).first
         : caHashSink.finish().first;
 
     if (expectedCAHash && expectedCAHash != hash)
diff --git a/src/libutil/archive.cc b/src/libutil/archive.cc
index 268a798d900..4e3ed4a7534 100644
--- a/src/libutil/archive.cc
+++ b/src/libutil/archive.cc
@@ -302,71 +302,6 @@ void parseDump(ParseSink & sink, Source & source)
 }
 
 
-struct RestoreSink : ParseSink
-{
-    Path dstPath;
-    AutoCloseFD fd;
-
-    void createDirectory(const Path & path) override
-    {
-        Path p = dstPath + path;
-        if (mkdir(p.c_str(), 0777) == -1)
-            throw SysError("creating directory '%1%'", p);
-    };
-
-    void createRegularFile(const Path & path) override
-    {
-        Path p = dstPath + path;
-        fd = open(p.c_str(), O_CREAT | O_EXCL | O_WRONLY | O_CLOEXEC, 0666);
-        if (!fd) throw SysError("creating file '%1%'", p);
-    }
-
-    void closeRegularFile() override
-    {
-        /* Call close explicitly to make sure the error is checked */
-        fd.close();
-    }
-
-    void isExecutable() override
-    {
-        struct stat st;
-        if (fstat(fd.get(), &st) == -1)
-            throw SysError("fstat");
-        if (fchmod(fd.get(), st.st_mode | (S_IXUSR | S_IXGRP | S_IXOTH)) == -1)
-            throw SysError("fchmod");
-    }
-
-    void preallocateContents(uint64_t len) override
-    {
-        if (!archiveSettings.preallocateContents)
-            return;
-
-#if HAVE_POSIX_FALLOCATE
-        if (len) {
-            errno = posix_fallocate(fd.get(), 0, len);
-            /* Note that EINVAL may indicate that the underlying
-               filesystem doesn't support preallocation (e.g. on
-               OpenSolaris).  Since preallocation is just an
-               optimisation, ignore it. */
-            if (errno && errno != EINVAL && errno != EOPNOTSUPP && errno != ENOSYS)
-                throw SysError("preallocating file of %1% bytes", len);
-        }
-#endif
-    }
-
-    void receiveContents(std::string_view data) override
-    {
-        writeFull(fd.get(), data);
-    }
-
-    void createSymlink(const Path & path, const std::string & target) override
-    {
-        Path p = dstPath + path;
-        nix::createSymlink(target, p);
-    }
-};
-
-
 void restorePath(const Path & path, Source & source)
 {
     RestoreSink sink;
diff --git a/src/libutil/experimental-features.cc b/src/libutil/experimental-features.cc
index 782331283ca..4f2ae03c46c 100644
--- a/src/libutil/experimental-features.cc
+++ b/src/libutil/experimental-features.cc
@@ -12,7 +12,7 @@ struct ExperimentalFeatureDetails
     std::string_view description;
 };
 
-constexpr std::array<ExperimentalFeatureDetails, 14> xpFeatureDetails = {{
+constexpr std::array<ExperimentalFeatureDetails, 15> xpFeatureDetails = {{
     {
         .tag = Xp::CaDerivations,
         .name = "ca-derivations",
@@ -70,6 +70,14 @@ constexpr std::array<ExperimentalFeatureDetails, 14> xpFeatureDetails = {{
             [`nix`](@docroot@/command-ref/new-cli/nix.md) for details.
         )",
     },
+    {
+        .tag = Xp::GitHashing,
+        .name = "git-hashing",
+        .description = R"(
+            Allow creating (content-addressed) store objects which are hashed via Git's hashing algorithm.
+            These store objects will not be understandable by older versions of Nix.
+        )",
+    },
     {
         .tag = Xp::RecursiveNix,
         .name = "recursive-nix",
diff --git a/src/libutil/experimental-features.hh b/src/libutil/experimental-features.hh
index add592ae624..f0e09a41f12 100644
--- a/src/libutil/experimental-features.hh
+++ b/src/libutil/experimental-features.hh
@@ -21,6 +21,7 @@ enum struct ExperimentalFeature
     ImpureDerivations,
     Flakes,
     NixCommand,
+    GitHashing,
     RecursiveNix,
     NoUrlLiterals,
     FetchClosure,
diff --git a/src/libutil/fs-sink.cc b/src/libutil/fs-sink.cc
new file mode 100644
index 00000000000..978b676ba4e
--- /dev/null
+++ b/src/libutil/fs-sink.cc
@@ -0,0 +1,104 @@
+#include <fcntl.h>
+
+#include "config.hh"
+#include "fs-sink.hh"
+
+namespace nix {
+
+
+struct RestoreSinkSettings : Config
+{
+    Setting<bool> preallocateContents{this, true, "preallocate-contents",
+        "Whether to preallocate files when writing objects with known size."};
+};
+
+static RestoreSinkSettings restoreSinkSettings;
+
+static GlobalConfig::Register r1(&restoreSinkSettings);
+
+
+void RestoreSink::createDirectory(const Path & path)
+{
+    Path p = dstPath + path;
+    if (mkdir(p.c_str(), 0777) == -1)
+        throw SysError("creating directory '%1%'", p);
+};
+
+void RestoreSink::createRegularFile(const Path & path, bool executable)
+{
+    Path p = dstPath + path;
+    fd = open(p.c_str(), O_CREAT | O_EXCL | O_WRONLY | O_CLOEXEC, executable ? 0777 : 0666);
+    if (!fd) throw SysError("creating file '%1%'", p);
+}
+
+void RestoreSink::closeRegularFile()
+{
+    /* Call close explicitly to make sure the error is checked */
+    fd.close();
+}
+
+void RestoreSink::isExecutable()
+{
+    struct stat st;
+    if (fstat(fd.get(), &st) == -1)
+        throw SysError("fstat");
+    if (fchmod(fd.get(), st.st_mode | (S_IXUSR | S_IXGRP | S_IXOTH)) == -1)
+        throw SysError("fchmod");
+}
+
+void RestoreSink::preallocateContents(uint64_t len)
+{
+    if (!restoreSinkSettings.preallocateContents)
+        return;
+
+#ifdef HAVE_POSIX_FALLOCATE
+    if (len) {
+        errno = posix_fallocate(fd.get(), 0, len);
+        /* Note that EINVAL may indicate that the underlying
+           filesystem doesn't support preallocation (e.g. on
+           OpenSolaris).  Since preallocation is just an
+           optimisation, ignore it. */
+        if (errno && errno != EINVAL && errno != EOPNOTSUPP && errno != ENOSYS)
+            throw SysError("preallocating file of %1% bytes", len);
+    }
+#endif
+}
+
+void RestoreSink::receiveContents(std::string_view data)
+{
+    writeFull(fd.get(), data);
+}
+
+void RestoreSink::createSymlink(const Path & path, const std::string & target)
+{
+    Path p = dstPath + path;
+    nix::createSymlink(target, p);
+}
+
+void RestoreSink::copyFile(const Path & source)
+{
+    FdSink sink(fd.get());
+    readFile(source, sink);
+}
+
+void RestoreSink::copyDirectory(const Path & source, const Path & destination)
+{
+    Path p = dstPath + destination;
+    createDirectory(destination);
+    for (auto & i : readDirectory(source)) {
+        struct stat st;
+        Path entry = source + "/" + i.name;
+        if (lstat(entry.c_str(), &st))
+            throw SysError("getting attributes of path '%1%'", entry);
+        if (S_ISREG(st.st_mode)) {
+            createRegularFile(destination + "/" + i.name, st.st_mode & S_IXUSR);
+            copyFile(entry);
+        } else if (S_ISDIR(st.st_mode))
+            copyDirectory(entry, destination + "/" + i.name);
+        else
+            throw Error("Unknown file: %s", entry);
+    }
+}
+
+
+}
diff --git a/src/libutil/fs-sink.hh b/src/libutil/fs-sink.hh
index ed6484e6111..afd41c9cc3b 100644
--- a/src/libutil/fs-sink.hh
+++ b/src/libutil/fs-sink.hh
@@ -13,13 +13,37 @@ struct ParseSink
 {
     virtual void createDirectory(const Path & path) { };
 
-    virtual void createRegularFile(const Path & path) { };
+    virtual void createRegularFile(const Path & path, bool executable = false) { };
     virtual void closeRegularFile() { };
     virtual void isExecutable() { };
     virtual void preallocateContents(uint64_t size) { };
     virtual void receiveContents(std::string_view data) { };
 
     virtual void createSymlink(const Path & path, const std::string & target) { };
+
+    virtual void copyFile(const Path & source) { };
+    virtual void copyDirectory(const Path & source, const Path & destination) { };
+};
+
+struct RestoreSink : ParseSink
+{
+    Path dstPath;
+    AutoCloseFD fd;
+
+
+    void createDirectory(const Path & path) override;
+
+    void createRegularFile(const Path & path, bool executable = false) override;
+    void closeRegularFile() override;
+    void isExecutable() override;
+    void preallocateContents(uint64_t size) override;
+    void receiveContents(std::string_view data) override;
+
+    void createSymlink(const Path & path, const std::string & target) override;
+
+    void copyFile(const Path & source) override;
+    void copyDirectory(const Path & source, const Path & destination) override;
 };
 
+
 }
diff --git a/src/libutil/git.cc b/src/libutil/git.cc
index f35c2fdb75c..7dbea3552f0 100644
--- a/src/libutil/git.cc
+++ b/src/libutil/git.cc
@@ -1,8 +1,239 @@
-#include "git.hh"
+#include <cerrno>
+#include <algorithm>
+#include <vector>
+#include <map>
 
 #include <regex>
 
+#include <strings.h> // for strcasecmp
+
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <unistd.h>
+#include <dirent.h>
+#include <fcntl.h>
+
+#include "util.hh"
+#include "config.hh"
+#include "hash.hh"
+
+#include "git.hh"
+#include "serialise.hh"
+
+using namespace std::string_literals;
+
 namespace nix {
+
+static void parse(ParseSink & sink, Source & source, const Path & path, std::function<Path(Hash)> getChildPath);
+
+// Converts a Path to a ParseSink
+void restoreGit(const Path & path, Source & source, std::function<Path(Hash)> getChildPath)
+{
+    RestoreSink sink;
+    sink.dstPath = path;
+    parseGit(sink, source, getChildPath);
+}
+
+void parseGit(ParseSink & sink, Source & source, std::function<Path(Hash)> getChildPath)
+{
+    parse(sink, source, "", getChildPath);
+}
+
+static std::string getStringUntil(Source & source, char byte)
+{
+    std::string s;
+    char n[1];
+    source(std::string_view { n, 1 });
+    while (*n != byte) {
+        s += *n;
+        source(std::string_view { n, 1 });
+    }
+    return s;
+}
+
+static std::string getString(Source & source, int n)
+{
+    std::string v;
+    v.resize(n);
+    source(v);
+    return v;
+}
+
+static void parse(ParseSink & sink, Source & source, const Path & path, std::function<Path(Hash)> getChildPath)
+{
+    experimentalFeatureSettings.require(Xp::GitHashing);
+
+    auto type = getString(source, 5);
+
+    if (type == "blob ") {
+        sink.createRegularFile(path);
+
+        unsigned long long size = std::stoi(getStringUntil(source, 0));
+
+        sink.preallocateContents(size);
+
+        unsigned long long left = size;
+        std::string buf;
+        buf.reserve(65536);
+
+        while (left) {
+            checkInterrupt();
+            buf.resize(std::min((unsigned long long)buf.capacity(), left));
+            source(buf);
+            sink.receiveContents(buf);
+            left -= buf.size();
+        }
+    } else if (type == "tree ") {
+        unsigned long long size = std::stoi(getStringUntil(source, 0));
+        unsigned long long left = size;
+
+        sink.createDirectory(path);
+
+        while (left) {
+            std::string perms = getStringUntil(source, ' ');
+            left -= perms.size();
+            left -= 1;
+
+            int perm = std::stoi(perms);
+            if (perm != 100644 && perm != 100755 && perm != 644 && perm != 755 && perm != 40000)
+              throw Error("Unknown Git permission: %d", perm);
+
+            std::string name = getStringUntil(source, 0);
+            left -= name.size();
+            left -= 1;
+
+            std::string hashs = getString(source, 20);
+            left -= 20;
+
+            Hash hash(htSHA1);
+            std::copy(hashs.begin(), hashs.end(), hash.hash);
+
+            Path entry0 = getChildPath(hash);
+            Path entry = absPath(entry0);
+
+            struct stat st;
+            if (lstat(entry.c_str(), &st))
+                throw SysError("getting attributes of path '%1%'", entry);
+
+            if (S_ISREG(st.st_mode)) {
+                if (perm == 40000)
+                    throw SysError("file is a file but expected to be a directory '%1%'", entry);
+
+                sink.createRegularFile(path + "/" + name, perm == 100755 || perm == 755);
+
+                sink.copyFile(entry);
+            } else if (S_ISDIR(st.st_mode)) {
+                if (perm != 40000)
+                    throw SysError("file is a directory but expected to be a file '%1%'", entry);
+
+                sink.copyDirectory(entry0, path + "/" + name);
+            } else throw Error("file '%1%' has an unsupported type", entry);
+        }
+    } else throw Error("input doesn't look like a Git object");
+}
+
+// TODO stream file into sink, rather than reading into vector
+GitMode dumpGitBlob(const Path & path, const struct stat st, Sink & sink)
+{
+    experimentalFeatureSettings.require(Xp::GitHashing);
+
+    auto s = fmt("blob %d\0%s"s, std::to_string(st.st_size), readFile(path));
+
+    std::string v;
+    std::copy(s.begin(), s.end(), std::back_inserter(v));
+    sink(v);
+    return st.st_mode & S_IXUSR
+        ? GitMode::Executable
+        : GitMode::Regular;
+}
+
+GitMode dumpGitTree(const GitTree & entries, Sink & sink)
+{
+    experimentalFeatureSettings.require(Xp::GitHashing);
+
+    std::vector<uint8_t> v1;
+
+    for (auto & i : entries) {
+        unsigned int mode;
+        switch (i.second.first) {
+        case GitMode::Directory: mode = 40000; break;
+        case GitMode::Executable: mode = 100755; break;
+        case GitMode::Regular: mode = 100644; break;
+        }
+        auto name = i.first;
+        if (i.second.first == GitMode::Directory)
+            name.pop_back();
+        auto s1 = fmt("%d %s", mode, name);
+        std::copy(s1.begin(), s1.end(), std::back_inserter(v1));
+        v1.push_back(0);
+        std::copy(i.second.second.hash, i.second.second.hash + 20, std::back_inserter(v1));
+    }
+
+    std::string v2;
+    auto s2 = fmt("tree %d"s, v1.size());
+    std::copy(s2.begin(), s2.end(), std::back_inserter(v2));
+    v2.push_back(0);
+    std::copy(v1.begin(), v1.end(), std::back_inserter(v2));
+
+    sink(v2);
+
+    return GitMode::Directory;
+}
+
+static std::pair<GitMode, Hash> dumpGitHashInternal(HashType ht, const Path & path, PathFilter & filter);
+
+static GitMode dumpGitInternal(HashType ht, const Path & path, Sink & sink, PathFilter & filter)
+{
+    struct stat st;
+    GitMode perm;
+    if (lstat(path.c_str(), &st))
+        throw SysError("getting attributes of path '%1%'", path);
+
+    if (S_ISREG(st.st_mode))
+        perm = dumpGitBlob(path, st, sink);
+    else if (S_ISDIR(st.st_mode)) {
+        GitTree entries;
+        for (auto & i : readDirectory(path))
+            if (filter(path + "/" + i.name)) {
+                auto result = dumpGitHashInternal(ht, path + "/" + i.name, filter);
+
+                // correctly observe git order, see
+                // https://github.com/mirage/irmin/issues/352
+                auto name = i.name;
+                if (result.first == GitMode::Directory)
+                    name += "/";
+
+                entries.insert_or_assign(name, result);
+            }
+        perm = dumpGitTree(entries, sink);
+    } else throw Error("file '%1%' has an unsupported type", path);
+
+    return perm;
+}
+
+
+static std::pair<GitMode, Hash> dumpGitHashInternal(HashType ht, const Path & path, PathFilter & filter)
+{
+    auto hashSink = new HashSink(ht);
+    auto perm = dumpGitInternal(ht, path, *hashSink, filter);
+    auto hash = hashSink->finish().first;
+    return std::pair { perm, hash };
+}
+
+Hash dumpGitHash(HashType ht, const Path & path, PathFilter & filter)
+{
+    experimentalFeatureSettings.require(Xp::GitHashing);
+
+    return dumpGitHashInternal(ht, path, filter).second;
+}
+
+void dumpGit(HashType ht, const Path & path, Sink & sink, PathFilter & filter)
+{
+    experimentalFeatureSettings.require(Xp::GitHashing);
+
+    dumpGitInternal(ht, path, sink, filter);
+}
+
 namespace git {
 
 std::optional<LsRemoteRefLine> parseLsRemoteLine(std::string_view line)
@@ -22,4 +253,5 @@ std::optional<LsRemoteRefLine> parseLsRemoteLine(std::string_view line)
 }
 
 }
+
 }
diff --git a/src/libutil/git.hh b/src/libutil/git.hh
index bf2b9a2869a..7563cb95750 100644
--- a/src/libutil/git.hh
+++ b/src/libutil/git.hh
@@ -5,8 +5,36 @@
 #include <string_view>
 #include <optional>
 
+#include "types.hh"
+#include "serialise.hh"
+#include "hash.hh"
+#include "fs-sink.hh"
+
 namespace nix {
 
+enum struct GitMode {
+    Directory,
+    Executable,
+    Regular,
+};
+
+void restoreGit(const Path & path, Source & source, std::function<Path(Hash)> getChildPath);
+
+void parseGit(ParseSink & sink, Source & source, std::function<Path(Hash)> getChildPath);
+
+// Dumps a single file to a sink
+GitMode dumpGitBlob(const Path & path, const struct stat st, Sink & sink);
+
+typedef std::map<std::string, std::pair<GitMode, Hash>> GitTree;
+
+// Dumps a representation of a git tree to a sink
+GitMode dumpGitTree(const GitTree & entries, Sink & sink);
+
+// Recursively dumps path, hashing as we go
+Hash dumpGitHash(HashType ht, const Path & path, PathFilter & filter = defaultPathFilter);
+
+void dumpGit(HashType ht, const Path & path, Sink & sink, PathFilter & filter = defaultPathFilter);
+
 namespace git {
 
 /**
diff --git a/src/libutil/hash.cc b/src/libutil/hash.cc
index 2c36d9d9498..f04c6b9041d 100644
--- a/src/libutil/hash.cc
+++ b/src/libutil/hash.cc
@@ -8,6 +8,7 @@
 #include "args.hh"
 #include "hash.hh"
 #include "archive.hh"
+#include "git.hh"
 #include "split.hh"
 #include "util.hh"
 
@@ -375,6 +376,13 @@ HashResult hashPath(
     return sink.finish();
 }
 
+HashResult hashGit(
+    HashType ht, const Path & path, PathFilter & filter)
+{
+    HashSink sink(ht);
+    dumpGit(ht, path, sink, filter);
+    return sink.finish();
+}
 
 Hash compressHash(const Hash & hash, unsigned int newSize)
 {
diff --git a/src/libutil/hash.hh b/src/libutil/hash.hh
index ae3ee40f4e3..0d4abd72b8f 100644
--- a/src/libutil/hash.hh
+++ b/src/libutil/hash.hh
@@ -145,18 +145,28 @@ std::string printHash16or32(const Hash & hash);
 Hash hashString(HashType ht, std::string_view s);
 
 /**
- * Compute the hash of the given file.
+ * Compute the hash of the given file, hashing its contents directly.
+ *
+ * (Metadata, such as the executable permission bit, is ignored.)
  */
 Hash hashFile(HashType ht, const Path & path);
 
 /**
- * Compute the hash of the given path.  The hash is defined as
- * (essentially) hashString(ht, dumpPath(path)).
+ * Compute the hash of the given path, serializing as a Nix Archive and
+ * then hashing that.
+ *
+ * The hash is defined as (essentially) hashString(ht, dumpPath(path)).
  */
 typedef std::pair<Hash, uint64_t> HashResult;
 HashResult hashPath(HashType ht, const Path & path,
     PathFilter & filter = defaultPathFilter);
 
+/**
+ * Compute the git blob/tree hash of the given path.
+ */
+HashResult hashGit(HashType ht, const Path & path,
+    PathFilter & filter = defaultPathFilter);
+
 /**
  * Compress a hash to the specified number of bytes by cyclically
  * XORing bytes together.
diff --git a/src/libutil/serialise.cc b/src/libutil/serialise.cc
index 3d5121a19fa..e5205ce79f0 100644
--- a/src/libutil/serialise.cc
+++ b/src/libutil/serialise.cc
@@ -74,6 +74,10 @@ void Source::operator () (char * data, size_t len)
     }
 }
 
+void Source::operator () (std::string_view data)
+{
+    (*this)((char *)data.data(), data.size());
+}
 
 void Source::drainInto(Sink & sink)
 {
diff --git a/src/libutil/serialise.hh b/src/libutil/serialise.hh
index 333c254ea8e..71c40c83a7d 100644
--- a/src/libutil/serialise.hh
+++ b/src/libutil/serialise.hh
@@ -72,6 +72,7 @@ struct Source
      * an error if it is not going to be available.
      */
     void operator () (char * data, size_t len);
+    void operator () (std::string_view data);
 
     /**
      * Store up to ‘len’ in the buffer pointed to by ‘data’, and
diff --git a/src/nix/add-to-store.cc b/src/nix/add-to-store.cc
index 39e5cc99dd2..f3e9249d2bb 100644
--- a/src/nix/add-to-store.cc
+++ b/src/nix/add-to-store.cc
@@ -2,6 +2,7 @@
 #include "common-args.hh"
 #include "store-api.hh"
 #include "archive.hh"
+#include "git.hh"
 
 using namespace nix;
 
@@ -34,11 +35,22 @@ struct CmdAddToStore : MixDryRun, StoreCommand
 
         auto narHash = hashString(htSHA256, sink.s);
 
-        Hash hash = narHash;
-        if (ingestionMethod == FileIngestionMethod::Flat) {
+        Hash hash { htSHA256 }; // throwaway def to appease C++
+        switch (ingestionMethod) {
+        case FileIngestionMethod::Recursive: {
+            hash = narHash;
+            break;
+        }
+        case FileIngestionMethod::Flat: {
             HashSink hsink(htSHA256);
             readFile(path, hsink);
             hash = hsink.finish().first;
+            break;
+        }
+        case FileIngestionMethod::Git: {
+            hash = dumpGitHash(htSHA1, path);
+            break;
+        }
         }
 
         ValidPathInfo info {
@@ -102,5 +114,26 @@ struct CmdAddPath : CmdAddToStore
     }
 };
 
+struct CmdAddGit : CmdAddToStore
+{
+    CmdAddGit()
+    {
+        ingestionMethod = FileIngestionMethod::Git;
+    }
+
+    std::string description() override
+    {
+        return "add a path to the Nix store";
+    }
+
+    std::string doc() override
+    {
+        return
+          #include "add-path.md"
+          ;
+    }
+};
+
 static auto rCmdAddFile = registerCommand2<CmdAddFile>({"store", "add-file"});
 static auto rCmdAddPath = registerCommand2<CmdAddPath>({"store", "add-path"});
+static auto rCmdAddGit = registerCommand2<CmdAddGit>({"store", "add-git"});
diff --git a/src/nix/hash.cc b/src/nix/hash.cc
index 9feca934557..368227ab628 100644
--- a/src/nix/hash.cc
+++ b/src/nix/hash.cc
@@ -5,6 +5,7 @@
 #include "shared.hh"
 #include "references.hh"
 #include "archive.hh"
+#include "git.hh"
 
 using namespace nix;
 
@@ -65,9 +66,11 @@ struct CmdHashBase : Command
     {
         switch (mode) {
         case FileIngestionMethod::Flat:
-            return  "print cryptographic hash of a regular file";
+            return "print cryptographic hash of a regular file";
         case FileIngestionMethod::Recursive:
             return "print cryptographic hash of the NAR serialisation of a path";
+        case FileIngestionMethod::Git:
+            return "print cryptographic hash of the Git serialisation of a path";
         default:
             assert(false);
         };
@@ -84,15 +87,21 @@ struct CmdHashBase : Command
                 hashSink = std::make_unique<HashSink>(ht);
 
             switch (mode) {
-            case FileIngestionMethod::Flat:
+            case FileIngestionMethod::Flat: {
                 readFile(path, *hashSink);
                 break;
-            case FileIngestionMethod::Recursive:
+            }
+            case FileIngestionMethod::Recursive: {
                 dumpPath(path, *hashSink);
                 break;
             }
+            case FileIngestionMethod::Git:
+                dumpGit(ht, path, *hashSink);
+                break;
+            }
+
+            auto h = hashSink->finish().first;
 
-            Hash h = hashSink->finish().first;
             if (truncate && h.hashSize > 20) h = compressHash(h, 20);
             logger->cout(h.to_string(base, base == SRI));
         }
@@ -133,6 +142,7 @@ struct CmdHash : NixMultiCommand
         : MultiCommand({
                 {"file", []() { return make_ref<CmdHashBase>(FileIngestionMethod::Flat);; }},
                 {"path", []() { return make_ref<CmdHashBase>(FileIngestionMethod::Recursive); }},
+                {"git", []() { return make_ref<CmdHashBase>(FileIngestionMethod::Git); }},
                 {"to-base16", []() { return make_ref<CmdToBase>(Base16); }},
                 {"to-base32", []() { return make_ref<CmdToBase>(Base32); }},
                 {"to-base64", []() { return make_ref<CmdToBase>(Base64); }},
diff --git a/tests/git-hashing/common.sh b/tests/git-hashing/common.sh
new file mode 100644
index 00000000000..5de96e74f16
--- /dev/null
+++ b/tests/git-hashing/common.sh
@@ -0,0 +1,11 @@
+source ../common.sh
+
+clearStore
+clearCache
+
+# Need backend to support git-hashing too
+requireDaemonNewerThan "2.18.0pre20230908"
+
+enableFeatures "git-hashing"
+
+restartDaemon
diff --git a/tests/git-hashing/fetching.sh b/tests/git-hashing/fetching.sh
new file mode 100644
index 00000000000..06ffcb35296
--- /dev/null
+++ b/tests/git-hashing/fetching.sh
@@ -0,0 +1,41 @@
+source common.sh
+
+[[ -n $(type -p git) ]] || skipTest "no git"
+
+repo=$TEST_ROOT/git
+
+rm -rf $repo $TEST_HOME/.cache/nix
+
+git init $repo
+git -C $repo config user.email "foobar@example.com"
+git -C $repo config user.name "Foobar"
+
+echo utrecht > $repo/hello
+touch $repo/.gitignore
+git -C $repo add hello .gitignore
+git -C $repo commit -m 'Bla1'
+
+echo world > $repo/hello
+git -C $repo commit -m 'Bla2' -a
+
+treeHash=$(git -C $repo rev-parse HEAD:)
+
+# Fetch the default branch.
+path=$(nix eval --raw --expr "(builtins.fetchTree { type = \"git\"; url = file://$repo; treeHash = \"$treeHash\"; }).outPath")
+[[ $(cat $path/hello) = world ]]
+
+# Submodules cause error.
+(! nix eval --raw --expr "(builtins.fetchTree { type = \"git\"; url = file://$repo; treeHash = \"$treeHash\"; submodules = true; }).outPath")
+
+# Check that we can substitute it from other places.
+nix copy --to file://$cacheDir $path
+nix-store --delete $path
+path2=$(nix eval --raw --expr "(builtins.fetchTree { type = \"git\"; url = file:///no-such-repo; treeHash = \"$treeHash\"; }).outPath" --substituters file://$cacheDir --option substitute true)
+[ $path2 = $path ]
+
+# HEAD should be the same path and tree hash as tree
+nix eval --impure --expr "(builtins.fetchTree { type = \"git\"; url = file://$repo; ref = \"HEAD\"; gitIngestion = true; })"
+treeHash2=$(nix eval --impure --raw --expr "(builtins.fetchTree { type = \"git\"; url = file://$repo; ref = \"HEAD\"; gitIngestion = true; }).treeHash")
+[ $treeHash = $treeHash2 ]
+path3=$(nix eval --impure --raw --expr "(builtins.fetchTree { type = \"git\"; url = file://$repo; ref = \"HEAD\"; gitIngestion = true; }).outPath")
+[ $path3 = $path ]
diff --git a/tests/git-hashing/local.mk b/tests/git-hashing/local.mk
new file mode 100644
index 00000000000..8e8218ccec8
--- /dev/null
+++ b/tests/git-hashing/local.mk
@@ -0,0 +1,8 @@
+git-hashing-tests := \
+  $(d)/simple.sh \
+  $(d)/fetching.sh
+
+install-tests-groups += git-hashing
+
+clean-files += \
+  $(d)/config.nix
diff --git a/tests/git-hashing/simple.sh b/tests/git-hashing/simple.sh
new file mode 100644
index 00000000000..144a9a5d6a8
--- /dev/null
+++ b/tests/git-hashing/simple.sh
@@ -0,0 +1,36 @@
+source common.sh
+
+try () {
+    hash=$(nix hash git --base16 --type sha1 $TEST_ROOT/hash-path)
+    if test "$hash" != "$1"; then
+        echo "git hash, expected $1, got $hash"
+        exit 1
+    fi
+}
+
+rm -rf $TEST_ROOT/hash-path
+mkdir $TEST_ROOT/hash-path
+echo "Hello World" > $TEST_ROOT/hash-path/hello
+
+try "117c62a8c5e01758bd284126a6af69deab9dbbe2"
+
+rm -rf $TEST_ROOT/dummy1
+echo Hello World! > $TEST_ROOT/dummy1
+path1=$(nix store add-git $TEST_ROOT/dummy1)
+hash1=$(nix-store -q --hash $path1)
+test "$hash1" = "sha256:1brffhvj2c0z6x8qismd43m0iy8dsgfmy10bgg9w11szway2wp9v"
+
+rm -rf $TEST_ROOT/dummy2
+mkdir -p $TEST_ROOT/dummy2
+echo Hello World! > $TEST_ROOT/dummy2/hello
+path2=$(nix store add-git $TEST_ROOT/dummy2)
+hash2=$(nix-store -q --hash $path2)
+test "$hash2" = "sha256:1vhv7zxam7x277q0y0jcypm7hwhccbzss81vkdgf0ww5sm2am4y0"
+
+rm -rf $TEST_ROOT/dummy3
+mkdir -p $TEST_ROOT/dummy3
+mkdir -p $TEST_ROOT/dummy3/hello
+echo Hello World! > $TEST_ROOT/dummy3/hello/hello
+path3=$(nix store add-git $TEST_ROOT/dummy3)
+hash3=$(nix-store -q --hash $path3)
+test "$hash3" = "sha256:1i2x80840igikhbyy7nqf08ymx3a6n83x1fzyrxvddf0sdl5nqvp"