diff --git a/Documentation/git-commit-graph.txt b/Documentation/git-commit-graph.txt
index 28d1fee505..46f7f7c573 100644
--- a/Documentation/git-commit-graph.txt
+++ b/Documentation/git-commit-graph.txt
@@ -57,11 +57,18 @@ or `--stdin-packs`.)
 With the `--append` option, include all commits that are present in the
 existing commit-graph file.
 +
-With the `--split` option, write the commit-graph as a chain of multiple
-commit-graph files stored in `<dir>/info/commit-graphs`. The new commits
-not already in the commit-graph are added in a new "tip" file. This file
-is merged with the existing file if the following merge conditions are
-met:
+With the `--split[=<strategy>]` option, write the commit-graph as a
+chain of multiple commit-graph files stored in
+`<dir>/info/commit-graphs`. Commit-graph layers are merged based on the
+strategy and other splitting options. The new commits not already in the
+commit-graph are added in a new "tip" file. This file is merged with the
+existing file if the following merge conditions are met:
+* If `--split=no-merge` is specified, a merge is never performed, and
+the remaining options are ignored. `--split=replace` overwrites the
+existing chain with a new one. A bare `--split` defers to the remaining
+options. (Note that merging a chain of commit graphs replaces the
+existing chain with a length-1 chain where the first and only
+incremental holds the entire graph).
 +
 * If `--size-multiple=<X>` is not specified, let `X` equal 2. If the new
 tip file would have `N` commits and the previous tip has `M` commits and
diff --git a/builtin/commit-graph.c b/builtin/commit-graph.c
index 03a8331e2b..9ceedbba07 100644
--- a/builtin/commit-graph.c
+++ b/builtin/commit-graph.c
@@ -9,7 +9,9 @@
 
 static char const * const builtin_commit_graph_usage[] = {
 	N_("git commit-graph verify [--object-dir <objdir>] [--shallow] [--[no-]progress]"),
-	N_("git commit-graph write [--object-dir <objdir>] [--append|--split] [--reachable|--stdin-packs|--stdin-commits] [--[no-]progress] <split options>"),
+	N_("git commit-graph write [--object-dir <objdir>] [--append] "
+	   "[--split[=<strategy>]] [--reachable|--stdin-packs|--stdin-commits] "
+	   "[--[no-]progress] <split options>"),
 	NULL
 };
 
@@ -19,7 +21,9 @@ static const char * const builtin_commit_graph_verify_usage[] = {
 };
 
 static const char * const builtin_commit_graph_write_usage[] = {
-	N_("git commit-graph write [--object-dir <objdir>] [--append|--split] [--reachable|--stdin-packs|--stdin-commits] [--[no-]progress] <split options>"),
+	N_("git commit-graph write [--object-dir <objdir>] [--append] "
+	   "[--split[=<strategy>]] [--reachable|--stdin-packs|--stdin-commits] "
+	   "[--[no-]progress] <split options>"),
 	NULL
 };
 
@@ -114,10 +118,29 @@ static int graph_verify(int argc, const char **argv)
 extern int read_replace_refs;
 static struct split_commit_graph_opts split_opts;
 
+static int write_option_parse_split(const struct option *opt, const char *arg,
+				    int unset)
+{
+	enum commit_graph_split_flags *flags = opt->value;
+
+	opts.split = 1;
+	if (!arg)
+		return 0;
+
+	if (!strcmp(arg, "no-merge"))
+		*flags = COMMIT_GRAPH_SPLIT_MERGE_PROHIBITED;
+	else if (!strcmp(arg, "replace"))
+		*flags = COMMIT_GRAPH_SPLIT_REPLACE;
+	else
+		die(_("unrecognized --split argument, %s"), arg);
+
+	return 0;
+}
+
 static int graph_write(int argc, const char **argv)
 {
 	struct string_list *pack_indexes = NULL;
-	struct string_list *commit_hex = NULL;
+	struct oidset commits = OIDSET_INIT;
 	struct object_directory *odb = NULL;
 	struct string_list lines;
 	int result = 0;
@@ -136,8 +159,10 @@ static int graph_write(int argc, const char **argv)
 		OPT_BOOL(0, "append", &opts.append,
 			N_("include all commits already in the commit-graph file")),
 		OPT_BOOL(0, "progress", &opts.progress, N_("force progress reporting")),
-		OPT_BOOL(0, "split", &opts.split,
-			N_("allow writing an incremental commit-graph file")),
+		OPT_CALLBACK_F(0, "split", &split_opts.flags, NULL,
+			N_("allow writing an incremental commit-graph file"),
+			PARSE_OPT_OPTARG | PARSE_OPT_NONEG,
+			write_option_parse_split),
 		OPT_INTEGER(0, "max-commits", &split_opts.max_commits,
 			N_("maximum number of commits in a non-base split commit-graph")),
 		OPT_INTEGER(0, "size-multiple", &split_opts.size_multiple,
@@ -188,7 +213,20 @@ static int graph_write(int argc, const char **argv)
 		if (opts.stdin_packs)
 			pack_indexes = &lines;
 		if (opts.stdin_commits) {
-			commit_hex = &lines;
+			struct string_list_item *item;
+			oidset_init(&commits, lines.nr);
+			for_each_string_list_item(item, &lines) {
+				struct object_id oid;
+				const char *end;
+
+				if (parse_oid_hex(item->string, &oid, &end)) {
+					error(_("unexpected non-hex object ID: "
+						"%s"), item->string);
+					return 1;
+				}
+
+				oidset_insert(&commits, &oid);
+			}
 			flags |= COMMIT_GRAPH_WRITE_CHECK_OIDS;
 		}
 
@@ -197,7 +235,7 @@ static int graph_write(int argc, const char **argv)
 
 	if (write_commit_graph(odb,
 			       pack_indexes,
-			       commit_hex,
+			       opts.stdin_commits ? &commits : NULL,
 			       flags,
 			       &split_opts))
 		result = 1;
diff --git a/commit-graph.c b/commit-graph.c
index 0d0d37787a..d11c836e1f 100644
--- a/commit-graph.c
+++ b/commit-graph.c
@@ -866,7 +866,7 @@ static void write_graph_chunk_data(struct hashfile *f, int hash_len,
 
 			if (edge_value >= 0)
 				edge_value += ctx->new_num_commits_in_base;
-			else {
+			else if (ctx->new_base_graph) {
 				uint32_t pos;
 				if (find_commit_in_graph(parent->item,
 							 ctx->new_base_graph,
@@ -897,7 +897,7 @@ static void write_graph_chunk_data(struct hashfile *f, int hash_len,
 
 			if (edge_value >= 0)
 				edge_value += ctx->new_num_commits_in_base;
-			else {
+			else if (ctx->new_base_graph) {
 				uint32_t pos;
 				if (find_commit_in_graph(parent->item,
 							 ctx->new_base_graph,
@@ -964,7 +964,7 @@ static void write_graph_chunk_extra_edges(struct hashfile *f,
 
 			if (edge_value >= 0)
 				edge_value += ctx->new_num_commits_in_base;
-			else {
+			else if (ctx->new_base_graph) {
 				uint32_t pos;
 				if (find_commit_in_graph(parent->item,
 							 ctx->new_base_graph,
@@ -1037,6 +1037,8 @@ static void close_reachable(struct write_commit_graph_context *ctx)
 {
 	int i;
 	struct commit *commit;
+	enum commit_graph_split_flags flags = ctx->split_opts ?
+		ctx->split_opts->flags : COMMIT_GRAPH_SPLIT_UNSPECIFIED;
 
 	if (ctx->report_progress)
 		ctx->progress = start_delayed_progress(
@@ -1066,8 +1068,9 @@ static void close_reachable(struct write_commit_graph_context *ctx)
 		if (!commit)
 			continue;
 		if (ctx->split) {
-			if (!parse_commit(commit) &&
-			    commit->graph_pos == COMMIT_NOT_FROM_GRAPH)
+			if ((!parse_commit(commit) &&
+			     commit->graph_pos == COMMIT_NOT_FROM_GRAPH) ||
+			    flags == COMMIT_GRAPH_SPLIT_REPLACE)
 				add_missing_parents(ctx, commit);
 		} else if (!parse_commit_no_graph(commit))
 			add_missing_parents(ctx, commit);
@@ -1133,13 +1136,13 @@ static void compute_generation_numbers(struct write_commit_graph_context *ctx)
 	stop_progress(&ctx->progress);
 }
 
-static int add_ref_to_list(const char *refname,
-			   const struct object_id *oid,
-			   int flags, void *cb_data)
+static int add_ref_to_set(const char *refname,
+			  const struct object_id *oid,
+			  int flags, void *cb_data)
 {
-	struct string_list *list = (struct string_list *)cb_data;
+	struct oidset *commits = (struct oidset *)cb_data;
 
-	string_list_append(list, oid_to_hex(oid));
+	oidset_insert(commits, oid);
 	return 0;
 }
 
@@ -1147,14 +1150,14 @@ int write_commit_graph_reachable(struct object_directory *odb,
 				 enum commit_graph_write_flags flags,
 				 const struct split_commit_graph_opts *split_opts)
 {
-	struct string_list list = STRING_LIST_INIT_DUP;
+	struct oidset commits = OIDSET_INIT;
 	int result;
 
-	for_each_ref(add_ref_to_list, &list);
-	result = write_commit_graph(odb, NULL, &list,
+	for_each_ref(add_ref_to_set, &commits);
+	result = write_commit_graph(odb, NULL, &commits,
 				    flags, split_opts);
 
-	string_list_clear(&list, 0);
+	oidset_clear(&commits);
 	return result;
 }
 
@@ -1203,39 +1206,46 @@ static int fill_oids_from_packs(struct write_commit_graph_context *ctx,
 	return 0;
 }
 
-static int fill_oids_from_commit_hex(struct write_commit_graph_context *ctx,
-				     struct string_list *commit_hex)
+static int fill_oids_from_commits(struct write_commit_graph_context *ctx,
+				  struct oidset *commits)
 {
-	uint32_t i;
+	uint32_t i = 0;
 	struct strbuf progress_title = STRBUF_INIT;
+	struct oidset_iter iter;
+	struct object_id *oid;
+
+	if (!oidset_size(commits))
+		return 0;
 
 	if (ctx->report_progress) {
 		strbuf_addf(&progress_title,
 			    Q_("Finding commits for commit graph from %d ref",
 			       "Finding commits for commit graph from %d refs",
-			       commit_hex->nr),
-			    commit_hex->nr);
+			       oidset_size(commits)),
+			    oidset_size(commits));
 		ctx->progress = start_delayed_progress(
 					progress_title.buf,
-					commit_hex->nr);
+					oidset_size(commits));
 	}
-	for (i = 0; i < commit_hex->nr; i++) {
-		const char *end;
-		struct object_id oid;
+
+	oidset_iter_init(commits, &iter);
+	while ((oid = oidset_iter_next(&iter))) {
 		struct commit *result;
 
-		display_progress(ctx->progress, i + 1);
-		if (!parse_oid_hex(commit_hex->items[i].string, &oid, &end) &&
-		    (result = lookup_commit_reference_gently(ctx->r, &oid, 1))) {
+		display_progress(ctx->progress, ++i);
+
+		result = lookup_commit_reference_gently(ctx->r, oid, 1);
+		if (result) {
 			ALLOC_GROW(ctx->oids.list, ctx->oids.nr + 1, ctx->oids.alloc);
 			oidcpy(&ctx->oids.list[ctx->oids.nr], &(result->object.oid));
 			ctx->oids.nr++;
 		} else if (ctx->check_oids) {
 			error(_("invalid commit object id: %s"),
-			    commit_hex->items[i].string);
+			      oid_to_hex(oid));
 			return -1;
 		}
 	}
+
 	stop_progress(&ctx->progress);
 	strbuf_release(&progress_title);
 
@@ -1287,6 +1297,8 @@ static uint32_t count_distinct_commits(struct write_commit_graph_context *ctx)
 static void copy_oids_to_commits(struct write_commit_graph_context *ctx)
 {
 	uint32_t i;
+	enum commit_graph_split_flags flags = ctx->split_opts ?
+		ctx->split_opts->flags : COMMIT_GRAPH_SPLIT_UNSPECIFIED;
 
 	ctx->num_extra_edges = 0;
 	if (ctx->report_progress)
@@ -1303,11 +1315,14 @@ static void copy_oids_to_commits(struct write_commit_graph_context *ctx)
 		ALLOC_GROW(ctx->commits.list, ctx->commits.nr + 1, ctx->commits.alloc);
 		ctx->commits.list[ctx->commits.nr] = lookup_commit(ctx->r, &ctx->oids.list[i]);
 
-		if (ctx->split &&
+		if (ctx->split && flags != COMMIT_GRAPH_SPLIT_REPLACE &&
 		    ctx->commits.list[ctx->commits.nr]->graph_pos != COMMIT_NOT_FROM_GRAPH)
 			continue;
 
-		parse_commit_no_graph(ctx->commits.list[ctx->commits.nr]);
+		if (ctx->split && flags == COMMIT_GRAPH_SPLIT_REPLACE)
+			parse_commit(ctx->commits.list[ctx->commits.nr]);
+		else
+			parse_commit_no_graph(ctx->commits.list[ctx->commits.nr]);
 
 		num_parents = commit_list_count(ctx->commits.list[ctx->commits.nr]->parents);
 		if (num_parents > 2)
@@ -1488,8 +1503,12 @@ static int write_commit_graph_file(struct write_commit_graph_context *ctx)
 		}
 
 		if (ctx->base_graph_name) {
-			const char *dest = ctx->commit_graph_filenames_after[
-						ctx->num_commit_graphs_after - 2];
+			const char *dest;
+			int idx = ctx->num_commit_graphs_after - 1;
+			if (ctx->num_commit_graphs_after > 1)
+				idx--;
+
+			dest = ctx->commit_graph_filenames_after[idx];
 
 			if (strcmp(ctx->base_graph_name, dest)) {
 				result = rename(ctx->base_graph_name, dest);
@@ -1529,6 +1548,7 @@ static void split_graph_merge_strategy(struct write_commit_graph_context *ctx)
 {
 	struct commit_graph *g;
 	uint32_t num_commits;
+	enum commit_graph_split_flags flags = COMMIT_GRAPH_SPLIT_UNSPECIFIED;
 	uint32_t i;
 
 	int max_commits = 0;
@@ -1539,24 +1559,36 @@ static void split_graph_merge_strategy(struct write_commit_graph_context *ctx)
 
 		if (ctx->split_opts->size_multiple)
 			size_mult = ctx->split_opts->size_multiple;
+
+		flags = ctx->split_opts->flags;
 	}
 
 	g = ctx->r->objects->commit_graph;
 	num_commits = ctx->commits.nr;
-	ctx->num_commit_graphs_after = ctx->num_commit_graphs_before + 1;
+	if (flags == COMMIT_GRAPH_SPLIT_REPLACE)
+		ctx->num_commit_graphs_after = 1;
+	else
+		ctx->num_commit_graphs_after = ctx->num_commit_graphs_before + 1;
 
-	while (g && (g->num_commits <= size_mult * num_commits ||
-		    (max_commits && num_commits > max_commits))) {
-		if (g->odb != ctx->odb)
-			break;
+	if (flags != COMMIT_GRAPH_SPLIT_MERGE_PROHIBITED &&
+	    flags != COMMIT_GRAPH_SPLIT_REPLACE) {
+		while (g && (g->num_commits <= size_mult * num_commits ||
+			    (max_commits && num_commits > max_commits))) {
+			if (g->odb != ctx->odb)
+				break;
 
-		num_commits += g->num_commits;
-		g = g->base_graph;
+			num_commits += g->num_commits;
+			g = g->base_graph;
 
-		ctx->num_commit_graphs_after--;
+			ctx->num_commit_graphs_after--;
+		}
 	}
 
-	ctx->new_base_graph = g;
+	if (flags != COMMIT_GRAPH_SPLIT_REPLACE)
+		ctx->new_base_graph = g;
+	else if (ctx->num_commit_graphs_after != 1)
+		BUG("split_graph_merge_strategy: num_commit_graphs_after "
+		    "should be 1 with --split=replace");
 
 	if (ctx->num_commit_graphs_after == 2) {
 		char *old_graph_name = get_commit_graph_filename(g->odb);
@@ -1756,13 +1788,14 @@ static void expire_commit_graphs(struct write_commit_graph_context *ctx)
 
 int write_commit_graph(struct object_directory *odb,
 		       struct string_list *pack_indexes,
-		       struct string_list *commit_hex,
+		       struct oidset *commits,
 		       enum commit_graph_write_flags flags,
 		       const struct split_commit_graph_opts *split_opts)
 {
 	struct write_commit_graph_context *ctx;
 	uint32_t i, count_distinct = 0;
 	int res = 0;
+	int replace = 0;
 
 	if (!commit_graph_compatible(the_repository))
 		return 0;
@@ -1797,6 +1830,9 @@ int write_commit_graph(struct object_directory *odb,
 				g = g->base_graph;
 			}
 		}
+
+		if (ctx->split_opts)
+			replace = ctx->split_opts->flags & COMMIT_GRAPH_SPLIT_REPLACE;
 	}
 
 	ctx->approx_nr_objects = approximate_object_count();
@@ -1828,12 +1864,12 @@ int write_commit_graph(struct object_directory *odb,
 			goto cleanup;
 	}
 
-	if (commit_hex) {
-		if ((res = fill_oids_from_commit_hex(ctx, commit_hex)))
+	if (commits) {
+		if ((res = fill_oids_from_commits(ctx, commits)))
 			goto cleanup;
 	}
 
-	if (!pack_indexes && !commit_hex)
+	if (!pack_indexes && !commits)
 		fill_oids_from_all_packs(ctx);
 
 	close_reachable(ctx);
@@ -1857,13 +1893,14 @@ int write_commit_graph(struct object_directory *odb,
 		goto cleanup;
 	}
 
-	if (!ctx->commits.nr)
+	if (!ctx->commits.nr && !replace)
 		goto cleanup;
 
 	if (ctx->split) {
 		split_graph_merge_strategy(ctx);
 
-		merge_commit_graphs(ctx);
+		if (!replace)
+			merge_commit_graphs(ctx);
 	} else
 		ctx->num_commit_graphs_after = 1;
 
diff --git a/commit-graph.h b/commit-graph.h
index e87a6f6360..98ef121924 100644
--- a/commit-graph.h
+++ b/commit-graph.h
@@ -6,6 +6,7 @@
 #include "string-list.h"
 #include "cache.h"
 #include "object-store.h"
+#include "oidset.h"
 
 #define GIT_TEST_COMMIT_GRAPH "GIT_TEST_COMMIT_GRAPH"
 #define GIT_TEST_COMMIT_GRAPH_DIE_ON_LOAD "GIT_TEST_COMMIT_GRAPH_DIE_ON_LOAD"
@@ -82,10 +83,17 @@ enum commit_graph_write_flags {
 	COMMIT_GRAPH_WRITE_CHECK_OIDS = (1 << 3)
 };
 
+enum commit_graph_split_flags {
+	COMMIT_GRAPH_SPLIT_UNSPECIFIED      = 0,
+	COMMIT_GRAPH_SPLIT_MERGE_PROHIBITED = 1,
+	COMMIT_GRAPH_SPLIT_REPLACE          = 2
+};
+
 struct split_commit_graph_opts {
 	int size_multiple;
 	int max_commits;
 	timestamp_t expire_time;
+	enum commit_graph_split_flags flags;
 };
 
 /*
@@ -99,7 +107,7 @@ int write_commit_graph_reachable(struct object_directory *odb,
 				 const struct split_commit_graph_opts *split_opts);
 int write_commit_graph(struct object_directory *odb,
 		       struct string_list *pack_indexes,
-		       struct string_list *commit_hex,
+		       struct oidset *commits,
 		       enum commit_graph_write_flags flags,
 		       const struct split_commit_graph_opts *split_opts);
 
diff --git a/oidset.c b/oidset.c
index f63ce818f6..15d4e18c37 100644
--- a/oidset.c
+++ b/oidset.c
@@ -36,6 +36,11 @@ void oidset_clear(struct oidset *set)
 	oidset_init(set, 0);
 }
 
+int oidset_size(struct oidset *set)
+{
+	return kh_size(&set->set);
+}
+
 void oidset_parse_file(struct oidset *set, const char *path)
 {
 	FILE *fp;
diff --git a/oidset.h b/oidset.h
index 3a2d9d1115..209ae7a173 100644
--- a/oidset.h
+++ b/oidset.h
@@ -54,6 +54,11 @@ int oidset_insert(struct oidset *set, const struct object_id *oid);
  */
 int oidset_remove(struct oidset *set, const struct object_id *oid);
 
+/**
+ * Returns the number of oids in the set.
+ */
+int oidset_size(struct oidset *set);
+
 /**
  * Remove all entries from the oidset, freeing any resources associated with
  * it.
diff --git a/t/helper/test-read-graph.c b/t/helper/test-read-graph.c
index f8a461767c..4846040363 100644
--- a/t/helper/test-read-graph.c
+++ b/t/helper/test-read-graph.c
@@ -7,26 +7,15 @@
 int cmd__read_graph(int argc, const char **argv)
 {
 	struct commit_graph *graph = NULL;
-	char *graph_name;
-	int open_ok;
-	int fd;
-	struct stat st;
 	struct object_directory *odb;
 
 	setup_git_directory();
 	odb = the_repository->objects->odb;
 
-	graph_name = get_commit_graph_filename(odb);
-
-	open_ok = open_commit_graph(graph_name, &fd, &st);
-	if (!open_ok)
-		die_errno(_("Could not open commit-graph '%s'"), graph_name);
-
-	graph = load_commit_graph_one_fd_st(fd, &st, odb);
+	graph = read_commit_graph_one(the_repository, odb);
 	if (!graph)
 		return 1;
 
-	FREE_AND_NULL(graph_name);
 
 	printf("header: %08x %d %d %d %d\n",
 		ntohl(*(uint32_t*)graph->data),
diff --git a/t/t5318-commit-graph.sh b/t/t5318-commit-graph.sh
index 9bf920ae17..e874a12696 100755
--- a/t/t5318-commit-graph.sh
+++ b/t/t5318-commit-graph.sh
@@ -43,7 +43,7 @@ test_expect_success 'create commits and repack' '
 test_expect_success 'exit with correct error on bad input to --stdin-commits' '
 	cd "$TRASH_DIRECTORY/full" &&
 	echo HEAD | test_expect_code 1 git commit-graph write --stdin-commits 2>stderr &&
-	test_i18ngrep "invalid commit object id" stderr &&
+	test_i18ngrep "unexpected non-hex object ID: HEAD" stderr &&
 	# valid tree OID, but not a commit OID
 	git rev-parse HEAD^{tree} | test_expect_code 1 git commit-graph write --stdin-commits 2>stderr &&
 	test_i18ngrep "invalid commit object id" stderr
diff --git a/t/t5324-split-commit-graph.sh b/t/t5324-split-commit-graph.sh
index b8b208fc3d..3378ec54cd 100755
--- a/t/t5324-split-commit-graph.sh
+++ b/t/t5324-split-commit-graph.sh
@@ -357,4 +357,34 @@ test_expect_success 'split across alternate where alternate is not split' '
 	test_cmp commit-graph .git/objects/info/commit-graph
 '
 
+test_expect_success '--split=no-merge always writes an incremental' '
+	test_when_finished rm -rf a b &&
+	rm -rf $graphdir $infodir/commit-graph &&
+	git reset --hard commits/2 &&
+	git rev-list HEAD~1 >a &&
+	git rev-list HEAD >b &&
+	git commit-graph write --split --stdin-commits <a &&
+	git commit-graph write --split=no-merge --stdin-commits <b &&
+	test_line_count = 2 $graphdir/commit-graph-chain
+'
+
+test_expect_success '--split=replace replaces the chain' '
+	rm -rf $graphdir $infodir/commit-graph &&
+	git reset --hard commits/3 &&
+	git rev-list -1 HEAD~2 >a &&
+	git rev-list -1 HEAD~1 >b &&
+	git rev-list -1 HEAD >c &&
+	git commit-graph write --split=no-merge --stdin-commits <a &&
+	git commit-graph write --split=no-merge --stdin-commits <b &&
+	git commit-graph write --split=no-merge --stdin-commits <c &&
+	test_line_count = 3 $graphdir/commit-graph-chain &&
+	git commit-graph write --stdin-commits --split=replace <b &&
+	test_path_is_missing $infodir/commit-graph &&
+	test_path_is_file $graphdir/commit-graph-chain &&
+	ls $graphdir/graph-*.graph >graph-files &&
+	test_line_count = 1 graph-files &&
+	verify_chain_files_exist $graphdir &&
+	graph_read_expect 2
+'
+
 test_done