diff --git a/channeld/channeld.c b/channeld/channeld.c
index 95802ad13715..620b191b311a 100644
--- a/channeld/channeld.c
+++ b/channeld/channeld.c
@@ -1930,12 +1930,19 @@ static void handle_unexpected_reestablish(struct peer *peer, const u8 *msg)
 	u64 next_revocation_number;
 	struct secret your_last_per_commitment_secret;
 	struct pubkey my_current_per_commitment_point;
+#if EXPERIMENTAL_FEATURES
+	struct tlv_channel_reestablish_tlvs *tlvs = tlv_channel_reestablish_tlvs_new(tmpctx);
+#endif
 
 	if (!fromwire_channel_reestablish(msg, &channel_id,
 					  &next_commitment_number,
 					  &next_revocation_number,
 					  &your_last_per_commitment_secret,
-					  &my_current_per_commitment_point))
+					  &my_current_per_commitment_point
+#if EXPERIMENTAL_FEATURES
+					  , tlvs
+#endif
+		    ))
 		peer_failed_warn(peer->pps, &peer->channel_id,
 				 "Bad channel_reestablish %s", tal_hex(peer, msg));
 
@@ -2474,6 +2481,9 @@ static void peer_reconnect(struct peer *peer,
 	struct secret last_local_per_commitment_secret;
 	bool dataloss_protect, check_extra_fields;
 	const u8 **premature_msgs = tal_arr(peer, const u8 *, 0);
+#if EXPERIMENTAL_FEATURES
+	struct tlv_channel_reestablish_tlvs *send_tlvs, *recv_tlvs;
+#endif
 
 	dataloss_protect = feature_negotiated(peer->our_features,
 					      peer->their_features,
@@ -2488,6 +2498,10 @@ static void peer_reconnect(struct peer *peer,
 	get_per_commitment_point(peer->next_index[LOCAL] - 1,
 				 &my_current_per_commitment_point, NULL);
 
+#if EXPERIMENTAL_FEATURES
+	send_tlvs = tlv_channel_reestablish_tlvs_new(tmpctx);
+#endif
+
 	/* BOLT #2:
 	 *
 	 *   - upon reconnection:
@@ -2525,14 +2539,22 @@ static void peer_reconnect(struct peer *peer,
 			 peer->revocations_received,
 			 last_remote_per_commit_secret,
 			 /* Can send any (valid) point here */
-			 &peer->remote_per_commit);
+			 &peer->remote_per_commit
+#if EXPERIMENTAL_FEATURES
+			 , send_tlvs
+#endif
+				);
 	} else {
 		msg = towire_channel_reestablish
 			(NULL, &peer->channel_id,
 			 peer->next_index[LOCAL],
 			 peer->revocations_received,
 			 last_remote_per_commit_secret,
-			 &my_current_per_commitment_point);
+			 &my_current_per_commitment_point
+#if EXPERIMENTAL_FEATURES
+			 , send_tlvs
+#endif
+				);
 	}
 
 	sync_crypto_write(peer->pps, take(msg));
@@ -2552,12 +2574,20 @@ static void peer_reconnect(struct peer *peer,
 					     msg) ||
 		 capture_premature_msg(&premature_msgs, msg));
 
+#if EXPERIMENTAL_FEATURES
+	recv_tlvs = tlv_channel_reestablish_tlvs_new(tmpctx);
+#endif
+
 	if (!fromwire_channel_reestablish(msg,
 					&channel_id,
 					&next_commitment_number,
 					&next_revocation_number,
 					&last_local_per_commitment_secret,
-					&remote_current_per_commitment_point)) {
+					&remote_current_per_commitment_point
+#if EXPERIMENTAL_FEATURES
+			 , recv_tlvs
+#endif
+		    )) {
 		peer_failed_warn(peer->pps,
 				 &peer->channel_id,
 				 "bad reestablish msg: %s %s",
diff --git a/closingd/closingd.c b/closingd/closingd.c
index 80c10adcaa87..83bffe4016c5 100644
--- a/closingd/closingd.c
+++ b/closingd/closingd.c
@@ -176,6 +176,9 @@ static void do_reconnect(struct per_peer_state *pps,
 	struct pubkey my_current_per_commitment_point, next_commitment_point;
 	struct secret their_secret;
 	struct tlv_shutdown_tlvs *tlvs;
+#if EXPERIMENTAL_FEATURES
+	struct tlv_channel_reestablish_tlvs *reestablish_tlvs = tlv_channel_reestablish_tlvs_new(tmpctx);
+#endif
 
 	my_current_per_commitment_point = get_per_commitment_point(next_index[LOCAL]-1);
 
@@ -201,7 +204,11 @@ static void do_reconnect(struct per_peer_state *pps,
 					 next_index[LOCAL],
 					 revocations_received,
 					 last_remote_per_commit_secret,
-					 &my_current_per_commitment_point);
+					 &my_current_per_commitment_point
+#if EXPERIMENTAL_FEATURES
+					 , reestablish_tlvs
+#endif
+		);
 	sync_crypto_write(pps, take(msg));
 
 	/* They might have already sent reestablish, which triggered us */
@@ -221,7 +228,11 @@ static void do_reconnect(struct per_peer_state *pps,
 					  &next_local_commitment_number,
 					  &next_remote_revocation_number,
 					  &their_secret,
-					  &next_commitment_point)) {
+					  &next_commitment_point
+#if EXPERIMENTAL_FEATURES
+					 , reestablish_tlvs
+#endif
+		    )) {
 		peer_failed_warn(pps, channel_id,
 				 "bad reestablish msg: %s %s",
 				 peer_wire_name(fromwire_peektype(channel_reestablish)),
diff --git a/openingd/dualopend.c b/openingd/dualopend.c
index 5ebae60b291f..ed5f58300198 100644
--- a/openingd/dualopend.c
+++ b/openingd/dualopend.c
@@ -3164,6 +3164,9 @@ static void do_reconnect_dance(struct state *state)
 		last_remote_per_commit_secret;
 	struct pubkey remote_current_per_commit_point;
 	struct tx_state *tx_state = state->tx_state;
+#if EXPERIMENTAL_FEATURES
+	struct tlv_channel_reestablish_tlvs *tlvs = tlv_channel_reestablish_tlvs_new(tmpctx);
+#endif
 
 	/* BOLT #2:
 	 *     - if `next_revocation_number` equals 0:
@@ -3177,7 +3180,11 @@ static void do_reconnect_dance(struct state *state)
 	msg = towire_channel_reestablish
 		(NULL, &state->channel_id, 1, 0,
 		 &last_remote_per_commit_secret,
-		 &state->first_per_commitment_point[LOCAL]);
+		 &state->first_per_commitment_point[LOCAL]
+#if EXPERIMENTAL_FEATURES
+		 , tlvs
+#endif
+			);
 	sync_crypto_write(state->pps, take(msg));
 
 	peer_billboard(false, "Sent reestablish, waiting for theirs");
@@ -3200,7 +3207,11 @@ static void do_reconnect_dance(struct state *state)
 			 &next_commitment_number,
 			 &next_revocation_number,
 			 &last_local_per_commit_secret,
-			 &remote_current_per_commit_point))
+			 &remote_current_per_commit_point
+#if EXPERIMENTAL_FEATURES
+			 , tlvs
+#endif
+				))
 		open_err_fatal(state, "Bad reestablish msg: %s %s",
 			       peer_wire_name(fromwire_peektype(msg)),
 			       tal_hex(msg, msg));
diff --git a/wire/extracted_peer_exp_upgradable.patch b/wire/extracted_peer_exp_upgradable.patch
new file mode 100644
index 000000000000..db26af74680e
--- /dev/null
+++ b/wire/extracted_peer_exp_upgradable.patch
@@ -0,0 +1,21 @@
+--- wire/peer_wire.csv	2021-05-09 15:44:59.166135652 +0930
++++ wire/peer_wire.csv.raw	2021-05-11 09:59:31.695459756 +0930
+@@ -221,6 +131,18 @@
+ msgdata,channel_reestablish,next_revocation_number,u64,
+ msgdata,channel_reestablish,your_last_per_commitment_secret,byte,32
+ msgdata,channel_reestablish,my_current_per_commitment_point,point,
++msgdata,channel_reestablish,tlvs,channel_reestablish_tlvs,
++tlvtype,channel_reestablish_tlvs,next_to_send,1
++tlvdata,channel_reestablish_tlvs,next_to_send,commitment_number,tu64,
++tlvtype,channel_reestablish_tlvs,desired_type,3
++tlvdata,channel_reestablish_tlvs,desired_type,type,channel_type,
++tlvtype,channel_reestablish_tlvs,current_type,5
++tlvdata,channel_reestablish_tlvs,current_type,type,channel_type,
++tlvtype,channel_reestablish_tlvs,upgradable,7
++tlvdata,channel_reestablish_tlvs,upgradable,upgrades,channel_type,...
++subtype,channel_type
++subtypedata,channel_type,len,u16,
++subtypedata,channel_type,features,byte,len
+ msgtype,announcement_signatures,259
+ msgdata,announcement_signatures,channel_id,channel_id,
+ msgdata,announcement_signatures,short_channel_id,short_channel_id,
diff --git a/wire/peer_wire.c b/wire/peer_wire.c
index 1f8fc3731306..afc60a2203bb 100644
--- a/wire/peer_wire.c
+++ b/wire/peer_wire.c
@@ -124,10 +124,17 @@ bool extract_channel_id(const u8 *in_pkt, struct channel_id *channel_id)
 	struct bitcoin_blkid ignored_chainhash;
 	struct secret ignored_secret;
 	struct tlv_open_channel_tlvs *tlvs = tlv_open_channel_tlvs_new(tmpctx);
+#if EXPERIMENTAL_FEATURES
+	struct tlv_channel_reestablish_tlvs *reestab_tlvs = tlv_channel_reestablish_tlvs_new(tmpctx);
+#endif
 
 	if (fromwire_channel_reestablish(in_pkt, channel_id,
 					 &ignored_u64, &ignored_u64,
-					 &ignored_secret, &ignored_pubkey))
+					 &ignored_secret, &ignored_pubkey
+#if EXPERIMENTAL_FEATURES
+					 , reestab_tlvs
+#endif
+		    ))
 		return true;
 	if (fromwire_open_channel(in_pkt, &ignored_chainhash,
 				  channel_id, &ignored_sat,