diff --git a/prdoc/pr_6755.prdoc b/prdoc/pr_6755.prdoc
new file mode 100644
index 000000000000..66763dc4e348
--- /dev/null
+++ b/prdoc/pr_6755.prdoc
@@ -0,0 +1,14 @@
+title: Collect transaction extensions by versions into custom metadata for v15
+
+doc:
+  - audience: [ Node Dev, Node Operator ]
+    description: |
+      This PR collects the transaction_extensions_by_version type information into the metadata V15 custom types.
+      This ensures the V15 contains enough information to work with multiple transaction extensions. The meaning of this field is identical to the one collected by the V16 unstable.
+      It includes indexes of extrinsics from the signed_extension field of the extrinsic metadata.
+
+crates:
+  - name: sp-metadata-ir
+    bump: patch
+  - name: frame-support-test
+    bump: none
diff --git a/substrate/frame/support/test/tests/pallet.rs b/substrate/frame/support/test/tests/pallet.rs
index 9df1f461bba2..be158ca6641d 100644
--- a/substrate/frame/support/test/tests/pallet.rs
+++ b/substrate/frame/support/test/tests/pallet.rs
@@ -1471,7 +1471,7 @@ fn pallet_item_docs_in_metadata() {
 
 #[test]
 fn metadata() {
-	use codec::Decode;
+	use codec::{Decode, Encode};
 	use frame_metadata::{v15::*, *};
 
 	let readme = "Very important information :D\n";
@@ -1931,13 +1931,24 @@ fn metadata() {
 		error_enum_ty: meta_type::<RuntimeError>(),
 	};
 
+	let custom_value: BTreeMap<u8, Vec<u32>> = [(0, vec![0])].into_iter().collect();
 	let expected_metadata: RuntimeMetadataPrefixed = RuntimeMetadataLastVersion::new(
 		pallets,
 		extrinsic,
 		meta_type::<Runtime>(),
 		vec![],
 		outer_enums,
-		CustomMetadata { map: Default::default() },
+		CustomMetadata {
+			map: [(
+				"transaction_extensions_by_version".into(),
+				CustomValueMetadata {
+					ty: meta_type::<BTreeMap<u8, Vec<u32>>>(),
+					value: custom_value.encode(),
+				},
+			)]
+			.into_iter()
+			.collect(),
+		},
 	)
 	.into();
 	let expected_metadata = match expected_metadata.1 {
diff --git a/substrate/primitives/metadata-ir/src/types.rs b/substrate/primitives/metadata-ir/src/types.rs
index af217ffe16ee..a6e51cbb3de0 100644
--- a/substrate/primitives/metadata-ir/src/types.rs
+++ b/substrate/primitives/metadata-ir/src/types.rs
@@ -201,6 +201,18 @@ impl IntoPortable for ExtrinsicMetadataIR {
 	}
 }
 
+/// The type of the transaction extensions by version field.
+pub type TrasactionExtensionsByVersion = BTreeMap<u8, Vec<u32>>;
+
+impl ExtrinsicMetadataIR {
+	/// Returns the transaction extensions by version.
+	pub fn transaction_extensions_by_version(&self) -> TrasactionExtensionsByVersion {
+		// Assume version 0 for all extensions.
+		let indexes = (0..self.extensions.len()).map(|index| index as u32).collect();
+		[(0, indexes)].iter().cloned().collect()
+	}
+}
+
 /// Metadata of a pallet's associated type.
 #[derive(Clone, PartialEq, Eq, Encode, Debug)]
 pub struct PalletAssociatedTypeMetadataIR<T: Form = MetaForm> {
diff --git a/substrate/primitives/metadata-ir/src/unstable.rs b/substrate/primitives/metadata-ir/src/unstable.rs
index d46ce3ec6a7d..dee63aa7fd71 100644
--- a/substrate/primitives/metadata-ir/src/unstable.rs
+++ b/substrate/primitives/metadata-ir/src/unstable.rs
@@ -162,9 +162,7 @@ impl From<TransactionExtensionMetadataIR> for TransactionExtensionMetadata {
 
 impl From<ExtrinsicMetadataIR> for ExtrinsicMetadata {
 	fn from(ir: ExtrinsicMetadataIR) -> Self {
-		// Assume version 0 for all extensions.
-		let indexes = (0..ir.extensions.len()).map(|index| index as u32).collect();
-		let transaction_extensions_by_version = [(0, indexes)].iter().cloned().collect();
+		let transaction_extensions_by_version = ir.transaction_extensions_by_version();
 
 		ExtrinsicMetadata {
 			versions: ir.versions,
diff --git a/substrate/primitives/metadata-ir/src/v15.rs b/substrate/primitives/metadata-ir/src/v15.rs
index ed315a31e6dc..f7c7d8be84fd 100644
--- a/substrate/primitives/metadata-ir/src/v15.rs
+++ b/substrate/primitives/metadata-ir/src/v15.rs
@@ -17,30 +17,43 @@
 
 //! Convert the IR to V15 metadata.
 
-use crate::OuterEnumsIR;
+use crate::{OuterEnumsIR, TrasactionExtensionsByVersion};
 
 use super::types::{
 	ExtrinsicMetadataIR, MetadataIR, PalletMetadataIR, RuntimeApiMetadataIR,
 	RuntimeApiMethodMetadataIR, RuntimeApiMethodParamMetadataIR, TransactionExtensionMetadataIR,
 };
 
+use codec::Encode;
 use frame_metadata::v15::{
-	CustomMetadata, ExtrinsicMetadata, OuterEnums, PalletMetadata, RuntimeApiMetadata,
-	RuntimeApiMethodMetadata, RuntimeApiMethodParamMetadata, RuntimeMetadataV15,
-	SignedExtensionMetadata,
+	CustomMetadata, CustomValueMetadata, ExtrinsicMetadata, OuterEnums, PalletMetadata,
+	RuntimeApiMetadata, RuntimeApiMethodMetadata, RuntimeApiMethodParamMetadata,
+	RuntimeMetadataV15, SignedExtensionMetadata,
 };
+use scale_info::meta_type;
 
 impl From<MetadataIR> for RuntimeMetadataV15 {
 	fn from(ir: MetadataIR) -> Self {
+		const TRANSACTION_EXTENSIONS_BY_VERSION: &str = "transaction_extensions_by_version";
+		let transaction_extensions_by_version = ir.extrinsic.transaction_extensions_by_version();
+
 		RuntimeMetadataV15::new(
 			ir.pallets.into_iter().map(Into::into).collect(),
 			ir.extrinsic.into(),
 			ir.ty,
 			ir.apis.into_iter().map(Into::into).collect(),
 			ir.outer_enums.into(),
-			// Substrate does not collect yet the custom metadata fields.
-			// This allows us to extend the V15 easily.
-			CustomMetadata { map: Default::default() },
+			CustomMetadata {
+				map: [(
+					TRANSACTION_EXTENSIONS_BY_VERSION.into(),
+					CustomValueMetadata {
+						ty: meta_type::<TrasactionExtensionsByVersion>(),
+						value: transaction_extensions_by_version.encode(),
+					},
+				)]
+				.into_iter()
+				.collect(),
+			},
 		)
 	}
 }