diff --git a/.gitignore b/.gitignore
index 5e56e471b3..612c0f6a0f 100644
--- a/.gitignore
+++ b/.gitignore
@@ -135,6 +135,7 @@
 /git-remote-ext
 /git-repack
 /git-replace
+/git-replay
 /git-request-pull
 /git-rerere
 /git-reset
diff --git a/Makefile b/Makefile
index 5776309365..05a504dc28 100644
--- a/Makefile
+++ b/Makefile
@@ -799,7 +799,6 @@ TEST_BUILTINS_OBJS += test-dump-split-index.o
 TEST_BUILTINS_OBJS += test-dump-untracked-cache.o
 TEST_BUILTINS_OBJS += test-env-helper.o
 TEST_BUILTINS_OBJS += test-example-decorate.o
-TEST_BUILTINS_OBJS += test-fast-rebase.o
 TEST_BUILTINS_OBJS += test-fsmonitor-client.o
 TEST_BUILTINS_OBJS += test-genrandom.o
 TEST_BUILTINS_OBJS += test-genzeros.o
@@ -1287,6 +1286,7 @@ BUILTIN_OBJS += builtin/remote-fd.o
 BUILTIN_OBJS += builtin/remote.o
 BUILTIN_OBJS += builtin/repack.o
 BUILTIN_OBJS += builtin/replace.o
+BUILTIN_OBJS += builtin/replay.o
 BUILTIN_OBJS += builtin/rerere.o
 BUILTIN_OBJS += builtin/reset.o
 BUILTIN_OBJS += builtin/rev-list.o
diff --git a/builtin.h b/builtin.h
index d560baa661..28280636da 100644
--- a/builtin.h
+++ b/builtin.h
@@ -211,6 +211,7 @@ int cmd_remote(int argc, const char **argv, const char *prefix);
 int cmd_remote_ext(int argc, const char **argv, const char *prefix);
 int cmd_remote_fd(int argc, const char **argv, const char *prefix);
 int cmd_repack(int argc, const char **argv, const char *prefix);
+int cmd_replay(int argc, const char **argv, const char *prefix);
 int cmd_rerere(int argc, const char **argv, const char *prefix);
 int cmd_reset(int argc, const char **argv, const char *prefix);
 int cmd_restore(int argc, const char **argv, const char *prefix);
diff --git a/t/helper/test-fast-rebase.c b/builtin/replay.c
similarity index 89%
rename from t/helper/test-fast-rebase.c
rename to builtin/replay.c
index 2bfab66b1b..e102749ab6 100644
--- a/t/helper/test-fast-rebase.c
+++ b/builtin/replay.c
@@ -1,17 +1,11 @@
 /*
- * "git fast-rebase" builtin command
- *
- * FAST: Forking Any Subprocesses (is) Taboo
- *
- * This is meant SOLELY as a demo of what is possible.  sequencer.c and
- * rebase.c should be refactored to use the ideas here, rather than attempting
- * to extend this file to replace those (unless Phillip or Dscho say that
- * refactoring is too hard and we need a clean slate, but I'm guessing that
- * refactoring is the better route).
+ * "git replay" builtin command
  */
 
 #define USE_THE_INDEX_VARIABLE
-#include "test-tool.h"
+#include "git-compat-util.h"
+
+#include "builtin.h"
 #include "cache-tree.h"
 #include "commit.h"
 #include "environment.h"
@@ -27,7 +21,8 @@
 #include "sequencer.h"
 #include "setup.h"
 #include "strvec.h"
-#include "tree.h"
+#include <oidset.h>
+#include <tree.h>
 
 static const char *short_commit_name(struct commit *commit)
 {
@@ -94,7 +89,7 @@ static struct commit *create_commit(struct tree *tree,
 	return (struct commit *)obj;
 }
 
-int cmd__fast_rebase(int argc, const char **argv)
+int cmd_replay(int argc, const char **argv, const char *prefix)
 {
 	struct commit *onto;
 	struct commit *last_commit = NULL, *last_picked_commit = NULL;
@@ -110,12 +105,6 @@ int cmd__fast_rebase(int argc, const char **argv)
 	struct strbuf branch_name = STRBUF_INIT;
 	int ret = 0;
 
-	/*
-	 * test-tool stuff doesn't set up the git directory by default; need to
-	 * do that manually.
-	 */
-	setup_git_directory();
-
 	if (argc == 2 && !strcmp(argv[1], "-h")) {
 		printf("Sorry, I am not a psychiatrist; I can not give you the help you need.  Oh, you meant usage...\n");
 		exit(129);
@@ -136,7 +125,7 @@ int cmd__fast_rebase(int argc, const char **argv)
 	if (repo_read_index(the_repository) < 0)
 		BUG("Could not read index");
 
-	repo_init_revisions(the_repository, &revs, NULL);
+	repo_init_revisions(the_repository, &revs, prefix);
 	revs.verbose_header = 1;
 	revs.max_parents = 1;
 	revs.cherry_mark = 1;
diff --git a/command-list.txt b/command-list.txt
index 54b2a50f5f..d74836ab21 100644
--- a/command-list.txt
+++ b/command-list.txt
@@ -160,6 +160,7 @@ git-reflog                              ancillarymanipulators           complete
 git-remote                              ancillarymanipulators           complete
 git-repack                              ancillarymanipulators           complete
 git-replace                             ancillarymanipulators           complete
+git-replay                              mainporcelain           history
 git-request-pull                        foreignscminterface             complete
 git-rerere                              ancillaryinterrogators
 git-reset                               mainporcelain           history
diff --git a/git.c b/git.c
index c67e44dd82..7068a184b0 100644
--- a/git.c
+++ b/git.c
@@ -594,6 +594,7 @@ static struct cmd_struct commands[] = {
 	{ "remote-fd", cmd_remote_fd, NO_PARSEOPT },
 	{ "repack", cmd_repack, RUN_SETUP },
 	{ "replace", cmd_replace, RUN_SETUP },
+	{ "replay", cmd_replay, RUN_SETUP },
 	{ "rerere", cmd_rerere, RUN_SETUP },
 	{ "reset", cmd_reset, RUN_SETUP },
 	{ "restore", cmd_restore, RUN_SETUP | NEED_WORK_TREE },
diff --git a/t/helper/test-tool.c b/t/helper/test-tool.c
index abe8a785eb..9ca1586de7 100644
--- a/t/helper/test-tool.c
+++ b/t/helper/test-tool.c
@@ -30,7 +30,6 @@ static struct test_cmd cmds[] = {
 	{ "dump-untracked-cache", cmd__dump_untracked_cache },
 	{ "env-helper", cmd__env_helper },
 	{ "example-decorate", cmd__example_decorate },
-	{ "fast-rebase", cmd__fast_rebase },
 	{ "fsmonitor-client", cmd__fsmonitor_client },
 	{ "genrandom", cmd__genrandom },
 	{ "genzeros", cmd__genzeros },
diff --git a/t/helper/test-tool.h b/t/helper/test-tool.h
index ea2672436c..a03bbfc6b2 100644
--- a/t/helper/test-tool.h
+++ b/t/helper/test-tool.h
@@ -24,7 +24,6 @@ int cmd__dump_untracked_cache(int argc, const char **argv);
 int cmd__dump_reftable(int argc, const char **argv);
 int cmd__env_helper(int argc, const char **argv);
 int cmd__example_decorate(int argc, const char **argv);
-int cmd__fast_rebase(int argc, const char **argv);
 int cmd__fsmonitor_client(int argc, const char **argv);
 int cmd__genrandom(int argc, const char **argv);
 int cmd__genzeros(int argc, const char **argv);
diff --git a/t/t6429-merge-sequence-rename-caching.sh b/t/t6429-merge-sequence-rename-caching.sh
index 75d3fd2dba..7670b72008 100755
--- a/t/t6429-merge-sequence-rename-caching.sh
+++ b/t/t6429-merge-sequence-rename-caching.sh
@@ -71,9 +71,8 @@ test_expect_success 'caching renames does not preclude finding new ones' '
 
 		git switch upstream &&
 
-		test-tool fast-rebase --onto HEAD upstream~1 topic &&
+		git replay --onto HEAD upstream~1 topic &&
 		git reset --hard topic &&
-		#git cherry-pick upstream~1..topic
 
 		git ls-files >tracked-files &&
 		test_line_count = 2 tracked-files &&
@@ -141,8 +140,7 @@ test_expect_success 'cherry-pick both a commit and its immediate revert' '
 		GIT_TRACE2_PERF="$(pwd)/trace.output" &&
 		export GIT_TRACE2_PERF &&
 
-		test-tool fast-rebase --onto HEAD upstream~1 topic &&
-		#git cherry-pick upstream~1..topic &&
+		git replay --onto HEAD upstream~1 topic &&
 
 		grep region_enter.*diffcore_rename trace.output >calls &&
 		test_line_count = 1 calls
@@ -200,9 +198,8 @@ test_expect_success 'rename same file identically, then reintroduce it' '
 		GIT_TRACE2_PERF="$(pwd)/trace.output" &&
 		export GIT_TRACE2_PERF &&
 
-		test-tool fast-rebase --onto HEAD upstream~1 topic &&
+		git replay --onto HEAD upstream~1 topic &&
 		git reset --hard topic &&
-		#git cherry-pick upstream~1..topic &&
 
 		git ls-files >tracked &&
 		test_line_count = 2 tracked &&
@@ -278,9 +275,8 @@ test_expect_success 'rename same file identically, then add file to old dir' '
 		GIT_TRACE2_PERF="$(pwd)/trace.output" &&
 		export GIT_TRACE2_PERF &&
 
-		test-tool fast-rebase --onto HEAD upstream~1 topic &&
+		git replay --onto HEAD upstream~1 topic &&
 		git reset --hard topic &&
-		#git cherry-pick upstream~1..topic &&
 
 		git ls-files >tracked &&
 		test_line_count = 4 tracked &&
@@ -356,8 +352,7 @@ test_expect_success 'cached dir rename does not prevent noticing later conflict'
 		GIT_TRACE2_PERF="$(pwd)/trace.output" &&
 		export GIT_TRACE2_PERF &&
 
-		test_must_fail test-tool fast-rebase --onto HEAD upstream~1 topic >output &&
-		#git cherry-pick upstream..topic &&
+		test_must_fail git replay --onto HEAD upstream~1 topic >output &&
 
 		grep region_enter.*diffcore_rename trace.output >calls &&
 		test_line_count = 2 calls
@@ -456,9 +451,8 @@ test_expect_success 'dir rename unneeded, then add new file to old dir' '
 		GIT_TRACE2_PERF="$(pwd)/trace.output" &&
 		export GIT_TRACE2_PERF &&
 
-		test-tool fast-rebase --onto HEAD upstream~1 topic &&
+		git replay --onto HEAD upstream~1 topic &&
 		git reset --hard topic &&
-		#git cherry-pick upstream..topic &&
 
 		grep region_enter.*diffcore_rename trace.output >calls &&
 		test_line_count = 2 calls &&
@@ -523,9 +517,8 @@ test_expect_success 'dir rename unneeded, then rename existing file into old dir
 		GIT_TRACE2_PERF="$(pwd)/trace.output" &&
 		export GIT_TRACE2_PERF &&
 
-		test-tool fast-rebase --onto HEAD upstream~1 topic &&
+		git replay --onto HEAD upstream~1 topic &&
 		git reset --hard topic &&
-		#git cherry-pick upstream..topic &&
 
 		grep region_enter.*diffcore_rename trace.output >calls &&
 		test_line_count = 3 calls &&
@@ -626,9 +619,8 @@ test_expect_success 'caching renames only on upstream side, part 1' '
 		GIT_TRACE2_PERF="$(pwd)/trace.output" &&
 		export GIT_TRACE2_PERF &&
 
-		test-tool fast-rebase --onto HEAD upstream~1 topic &&
+		git replay --onto HEAD upstream~1 topic &&
 		git reset --hard topic &&
-		#git cherry-pick upstream..topic &&
 
 		grep region_enter.*diffcore_rename trace.output >calls &&
 		test_line_count = 1 calls &&
@@ -685,9 +677,8 @@ test_expect_success 'caching renames only on upstream side, part 2' '
 		GIT_TRACE2_PERF="$(pwd)/trace.output" &&
 		export GIT_TRACE2_PERF &&
 
-		test-tool fast-rebase --onto HEAD upstream~1 topic &&
+		git replay --onto HEAD upstream~1 topic &&
 		git reset --hard topic &&
-		#git cherry-pick upstream..topic &&
 
 		grep region_enter.*diffcore_rename trace.output >calls &&
 		test_line_count = 2 calls &&
