diff --git a/config_test.go b/config_test.go
index 37c9120..761c269 100644
--- a/config_test.go
+++ b/config_test.go
@@ -742,8 +742,8 @@ func TestWriteMode_Validity(t *testing.T) {
 	if !WriteModeMemiavlOnly.IsValid() {
 		t.Error("memiavl_only should be valid")
 	}
-	if WriteModeCosmosOnly.IsValid() {
-		t.Error("cosmos_only should not be valid in v2 (deprecated — use migration)")
+	if !WriteModeCosmosOnly.IsValid() {
+		t.Error("cosmos_only should be valid (deprecated, but accepted by stable seid v6.5.1)")
 	}
 	if WriteMode("invalid").IsValid() {
 		t.Error("'invalid' should not be valid")
diff --git a/defaults.go b/defaults.go
index be98a8b..bce77e6 100644
--- a/defaults.go
+++ b/defaults.go
@@ -115,9 +115,12 @@ func baseDefaults() *SeiConfig {
 			PruningInterval:     "0",
 			SnapshotKeepRecent:  2,
 			IAVLDisableFastNode: true,
+			// WriteMode tracks the stable released seid (v6.5.1), which accepts
+			// cosmos_only and rejects memiavl_only. Nightly/main callers override
+			// to memiavl_only. Bump this default when 6.6.0 ships memiavl_only.
 			StateCommit: StateCommitConfig{
 				Enable:    true,
-				WriteMode: WriteModeMemiavlOnly,
+				WriteMode: WriteModeCosmosOnly,
 				ReadMode:  ReadModeCosmosOnly,
 			},
 			StateStore: StateStoreConfig{
@@ -128,7 +131,7 @@ func baseDefaults() *SeiConfig {
 				PruneIntervalSeconds: 600,
 				ImportNumWorkers:     1,
 				KeepLastVersion:      true,
-				WriteMode:            WriteModeMemiavlOnly,
+				WriteMode:            WriteModeCosmosOnly,
 				ReadMode:             ReadModeCosmosOnly,
 			},
 			ReceiptStore: ReceiptStoreConfig{
diff --git a/migrate_test.go b/migrate_test.go
index f35e5e7..b785c47 100644
--- a/migrate_test.go
+++ b/migrate_test.go
@@ -380,7 +380,7 @@ func TestDefaultMigrations_Valid(t *testing.T) {
 
 // v1ToV2Migration returns the v1→v2 migration from DefaultMigrations for tests
 // that exercise the rename transform directly (bypassing post-migration
-// validation, which rejects unknown/deprecated WriteMode values).
+// validation, which rejects unknown WriteMode values).
 func v1ToV2Migration(t *testing.T) Migration {
 	t.Helper()
 	for _, m := range DefaultMigrations() {
diff --git a/types.go b/types.go
index e46d099..aa14744 100644
--- a/types.go
+++ b/types.go
@@ -89,7 +89,11 @@ func (m WriteMode) IsValid() bool {
 	switch m {
 	case WriteModeMemiavlOnly, WriteModeMigrateEVM, WriteModeEVMMigrated,
 		WriteModeMigrateAllButBank, WriteModeAllMigratedButBank,
-		WriteModeMigrateBank, WriteModeFlatKVOnly, WriteModeTestOnlyDualWrite:
+		WriteModeMigrateBank, WriteModeFlatKVOnly, WriteModeTestOnlyDualWrite,
+		// Deprecated v1 modes remain valid: the stable released seid (v6.5.1)
+		// still accepts them and rejects the v2 names. The v1→v2 migration
+		// renames them; validation must not reject configs targeting v6.5.1.
+		WriteModeCosmosOnly, WriteModeDualWrite, WriteModeSplitWrite:
 		return true
 	default:
 		return false
diff --git a/version.json b/version.json
index 2b10809..ae175f4 100644
--- a/version.json
+++ b/version.json
@@ -1,3 +1,3 @@
 {
-  "version": "v0.0.18"
+  "version": "v0.0.19"
 }