diff --git a/CHANGES.txt b/CHANGES.txt
index d26d748432..bca3b56a37 100644
--- a/CHANGES.txt
+++ b/CHANGES.txt
@@ -1,4 +1,6 @@
 5.0.9
+Merged from 4.1:
+ * Add Paxos v2 option and informatin in cassandra.yaml (CASSANDRA-21316)
 Merged from 4.0:
  * Backport CASSANDRA-17810 fix and improve RTBoundValidator error messages (CASSANDRA-18282)
 
diff --git a/conf/cassandra.yaml b/conf/cassandra.yaml
index e3472fc227..69b82fc99a 100644
--- a/conf/cassandra.yaml
+++ b/conf/cassandra.yaml
@@ -1572,6 +1572,35 @@ dynamic_snitch_reset_interval: 600000ms
 # until the pinned host was 20% worse than the fastest.
 dynamic_snitch_badness_threshold: 1.0
 
+# Paxos variant for lightweight transactions (LWTs)
+# Options:
+#   v1
+#          - Legacy Paxos. Expect 4RTs for a write and 3RTs for a read. (default)
+#
+#   v1_without_linearizable_reads_or_rejected_writes
+#          - Legacy Paxos. Expect 4RTs for a write and 2RTs for a read.
+#            With legacy semantics for read/read and rejected write linearizability, i.e. not guaranteed.
+#
+#   v2
+#          - Optimized Paxos. Expect 2RTs for a write, and either 1RT or 2RT for a read. (recommended)
+#
+#   v2_without_linearizable_reads
+#          - Optimized Paxos. Expect 2RTs for a write and 1RT for a read.
+#
+#   v2_without_linearizable_reads_or_rejected_writes
+#          - Optimized Paxos. Expect 2RTs for a write and 1RT for a read.
+#            With legacy semantics for read/read and rejected write linearizability, i.e. not guaranteed.
+#
+# To upgrade from v1:
+#   1. Ensure all nodes are on same Cassandra version 4.1+.
+#   2. Run `nodetool repair --full -pr` on each node.
+#   3. Set paxos_variant: v2 on each node and rolling restart.
+#   Rollback is safe: revert to v1 and rolling restart. No data migration needed.
+#
+# With any v2 variant and `paxos_state_purging: repaired` it is safe to use ANY Commit consistency.
+#
+#paxos_variant: v1
+
 # Configures Java crypto provider. By default, it will use DefaultCryptoProvider
 # which will install Amazon Correto Crypto Provider.
 #
diff --git a/conf/cassandra_latest.yaml b/conf/cassandra_latest.yaml
index 956e1e803b..7fb9c7bc6b 100644
--- a/conf/cassandra_latest.yaml
+++ b/conf/cassandra_latest.yaml
@@ -1556,6 +1556,35 @@ dynamic_snitch_reset_interval: 600000ms
 # until the pinned host was 20% worse than the fastest.
 dynamic_snitch_badness_threshold: 1.0
 
+# Paxos variant for lightweight transactions (LWTs)
+# Options:
+#   v1
+#          - Legacy Paxos. Expect 4RTs for a write and 3RTs for a read. (default)
+#
+#   v1_without_linearizable_reads_or_rejected_writes
+#          - Legacy Paxos. Expect 4RTs for a write and 2RTs for a read.
+#            With legacy semantics for read/read and rejected write linearizability, i.e. not guaranteed.
+#
+#   v2
+#          - Optimized Paxos. Expect 2RTs for a write, and either 1RT or 2RT for a read. (recommended)
+#
+#   v2_without_linearizable_reads
+#          - Optimized Paxos. Expect 2RTs for a write and 1RT for a read.
+#
+#   v2_without_linearizable_reads_or_rejected_writes
+#          - Optimized Paxos. Expect 2RTs for a write and 1RT for a read.
+#            With legacy semantics for read/read and rejected write linearizability, i.e. not guaranteed.
+#
+# To upgrade from v1:
+#   1. Ensure all nodes are on same Cassandra version 4.1+.
+#   2. Run `nodetool repair --full -pr` on each node.
+#   3. Set paxos_variant: v2 on each node and rolling restart.
+#   Rollback is safe: revert to v1 and rolling restart. No data migration needed.
+#
+# With any v2 variant and `paxos_state_purging: repaired` it is safe to use ANY Commit consistency.
+#
+paxos_variant: v2
+
 # Configures Java crypto provider. By default, it will use DefaultCryptoProvider
 # which will install Amazon Correto Crypto Provider.
 #