diff --git a/README.md b/README.md
index 7b73f49..5d5af9d 100644
--- a/README.md
+++ b/README.md
@@ -89,6 +89,7 @@ partial, alternate, and planned behavior.
 | `-a, --archive` | Archive mode: enables `-c -m -M` (no `-s`) |
 | `-m` | Multithreading mode |
 | `-s` | Chunk serialization (batch all files per chunk) |
+| `--secluded-args` | Accepted as an rsync compatibility option with no effect; `-s` remains chunk serialization. |
 | `-f, --sendfile` | Sendfile zero-copy. Incompatible with `-c` / `-s`. TCP only. |
 | `-M, --preserve` | Preserve supported file metadata (mode and mtime; ownership and atime are unsupported) |
 | `-n, --dry-run` | Scan and print what would be transferred |
@@ -361,6 +362,11 @@ particular, FastSync currently uses `-p` for SSH port, `-s` for chunk
 serialization, and `-S` for sparse handling. These meanings must be reconciled
 before FastSync can claim full rsync CLI compatibility.
 
+`--secluded-args` is accepted as a long-form compatibility no-op. It does not
+change FastSync's transport or protocol behavior. The rsync short form `-s` is
+intentionally not aliased because it remains FastSync's chunk-serialization
+option.
+
 ## Client Options
 
 ### Selection and transfer
diff --git a/RSYNC_COMPAT.md b/RSYNC_COMPAT.md
index 1370073..4b224a1 100644
--- a/RSYNC_COMPAT.md
+++ b/RSYNC_COMPAT.md
@@ -9,7 +9,8 @@ This document maps rsync's full feature set to FastSync's current implementation
 | ✅ Implemented | 35 | Feature works end-to-end |
 | 🔀 Alt Arg | 4 | Functionality exists but under different flag/semantics |
 | ⚠️ Partial | 5 | Flag parsed/stored but behavior incomplete |
-| ❌ Not Implemented | 97 | Flag not recognized or no behavior |
+| 🔄 Compatibility No-op | 1 | Flag is accepted for CLI compatibility but has no effect |
+| ❌ Not Implemented | 96 | Flag not recognized or no behavior |
 | **Total** | **141** | |
 
 ---
@@ -233,7 +234,7 @@ This document maps rsync's full feature set to FastSync's current implementation
 | `--protocol=NUM` | Force older protocol version | ❌ Not Implemented | |
 | `--iconv=CONVERT_SPEC` | Charset conversion | ❌ Not Implemented | |
 | `--checksum-seed=NUM` | Set checksum seed | ❌ Not Implemented | |
-| `-s`, `--secluded-args` | Use protocol to send args | ❌ Not Implemented | |
+| `--secluded-args` | Use protocol to send args | 🔄 Compatibility No-op | Accepted for CLI compatibility; it does not change FastSync transport or protocol behavior. `-s` remains chunk serialization. |
 | `--no-OPTION` | Turn off implied option | ❌ Not Implemented | |
 
 ---
diff --git a/src/client/client_cli.c b/src/client/client_cli.c
index 0df49a8..924b37b 100644
--- a/src/client/client_cli.c
+++ b/src/client/client_cli.c
@@ -186,6 +186,7 @@ static int config_add_pattern(char*** patterns, int* count, const char* value,
 
 typedef enum {
   OPT_FLAG,
+  OPT_NOOP,
   OPT_STRING,
   OPT_POS_INT,
   OPT_NONNEG_INT,
@@ -196,10 +197,10 @@ typedef struct {
   const char* name;
   const char* alias;
   OptKind kind;
-  size_t offset; /* offsetof of the target field in Config */
+  size_t offset; /* offsetof of the target field in Config, or 0 for OPT_NOOP */
 } OptionEntry;
 
-/* Options that map directly onto a Config field with no side effects. */
+/* Options parsed directly into Config, plus compatibility options with no effect. */
 static const OptionEntry OPTION_TABLE[] = {
     {"--dry-run", "-n", OPT_FLAG, offsetof(Config, dry_run)},
     {"--remove-source-files", NULL, OPT_FLAG, offsetof(Config, remove_source_files)},
@@ -213,6 +214,7 @@ static const OptionEntry OPTION_TABLE[] = {
     {"--stats", NULL, OPT_FLAG, offsetof(Config, stats)},
     {"--human-readable", "-h", OPT_FLAG, offsetof(Config, human_readable)},
     {"--partial", NULL, OPT_FLAG, offsetof(Config, partial)},
+    {"--secluded-args", NULL, OPT_NOOP, 0},
     {"--links", "-l", OPT_FLAG, offsetof(Config, follow_symlinks)},
     {"--copy-links", NULL, OPT_FLAG, offsetof(Config, copy_links)},
     {"--safe-links", NULL, OPT_FLAG, offsetof(Config, safe_links)},
@@ -254,11 +256,16 @@ static const OptionEntry* find_table_option(const char* arg) {
 }
 
 static int apply_table_option(Config* config, const OptionEntry* entry, const char* value) {
+  if (entry->kind == OPT_NOOP)
+    return 0;
+
   void* field = (char*)config + entry->offset;
   switch (entry->kind) {
   case OPT_FLAG:
     *(bool*)field = true;
     return 0;
+  case OPT_NOOP:
+    return 0;
   case OPT_STRING:
     return set_string_option((char**)field, value, entry->name);
   case OPT_POS_INT:
diff --git a/src/client/usage.c b/src/client/usage.c
index 9201ef5..9025a82 100644
--- a/src/client/usage.c
+++ b/src/client/usage.c
@@ -37,6 +37,7 @@ void print_usage(void) {
          DELTA_MAX_FILE_SIZE);
   printf("  -m                  Enable multithreading\n");
   printf("  -s                  Enable chunk serialization\n");
+  printf("  --secluded-args    Accept rsync compatibility option (no effect)\n");
   printf("  -f                  Enable sendfile (TCP only, not with -c or -s)\n");
   printf("  -v, --verbose       Enable debug logging\n");
   printf("  -q, --quiet         Suppress non-error output\n");
diff --git a/tests/test_client_cli.c b/tests/test_client_cli.c
index d490239..22e4fb3 100644
--- a/tests/test_client_cli.c
+++ b/tests/test_client_cli.c
@@ -434,6 +434,29 @@ static void test_parse_args_fsync() {
   config_delete(cfg);
 }
 
+/* --secluded-args is accepted for compatibility but has no effect. */
+static void test_parse_args_secluded_args() {
+  Config* cfg = config_create();
+  char* argv[] = {"fastsync", "--secluded-args", "/src", "/dst"};
+  int positional_args[2];
+  int positional_count = 0;
+
+  EXPECT_EQ_INT(parse_args(cfg, 4, argv, positional_args, &positional_count), 0);
+  EXPECT_FALSE(cfg->use_chunk_serialization);
+  config_delete(cfg);
+}
+
+static void test_parse_args_short_s_remains_chunk_serialization() {
+  Config* cfg = config_create();
+  char* argv[] = {"fastsync", "-s", "/src", "/dst"};
+  int positional_args[2];
+  int positional_count = 0;
+
+  EXPECT_EQ_INT(parse_args(cfg, 4, argv, positional_args, &positional_count), 0);
+  EXPECT_TRUE(cfg->use_chunk_serialization);
+  config_delete(cfg);
+}
+
 static void test_parse_args_8_bit_output() {
   Config* cfg = config_create();
   char* long_argv[] = {"fastsync", "--8-bit-output", "/src", "/dst"};
@@ -484,7 +507,6 @@ static void test_parse_args_rejects_unsupported_stderr_modes() {
   }
   log_set_stderr_mode(LOG_STDERR_ERRORS);
 }
-
 void test_client_cli() {
   test_validate_config_required_paths();
   test_validate_config_incompatible_options();
@@ -517,4 +539,6 @@ void test_client_cli() {
   test_parse_args_8_bit_output();
   test_parse_args_stderr_modes();
   test_parse_args_rejects_unsupported_stderr_modes();
+  test_parse_args_secluded_args();
+  test_parse_args_short_s_remains_chunk_serialization();
 }