diff --git a/changelogs/room_versions/newsfragments/2070.clarification b/changelogs/room_versions/newsfragments/2070.clarification
new file mode 100644
index 00000000..7d0208cd
--- /dev/null
+++ b/changelogs/room_versions/newsfragments/2070.clarification
@@ -0,0 +1 @@
+Refactor PDU definitions to reduce duplication.
diff --git a/content/rooms/v1.md b/content/rooms/v1.md
index 1b950f11..773d7caa 100644
--- a/content/rooms/v1.md
+++ b/content/rooms/v1.md
@@ -51,7 +51,7 @@ inconsistencies may occur.
 
 Events in version 1 rooms have the following structure:
 
-{{% definition path="api/server-server/definitions/pdu" %}}
+{{% definition path="api/server-server/definitions/pdu_v1" %}}
 
 #### Deprecated event content schemas
 
diff --git a/content/rooms/v2.md b/content/rooms/v2.md
index f9980261..f0ea1ac7 100644
--- a/content/rooms/v2.md
+++ b/content/rooms/v2.md
@@ -49,7 +49,7 @@ completeness.
 
 Events in rooms of this version have the following structure:
 
-{{% definition path="api/server-server/definitions/pdu" %}}
+{{% definition path="api/server-server/definitions/pdu_v1" %}}
 
 #### Deprecated event content schemas
 
diff --git a/data/api/server-server/definitions/components/auth_events_prev_events_v4.yaml b/data/api/server-server/definitions/components/auth_events_prev_events_v4.yaml
new file mode 100644
index 00000000..fabfef82
--- /dev/null
+++ b/data/api/server-server/definitions/components/auth_events_prev_events_v4.yaml
@@ -0,0 +1,45 @@
+# Copyright 2025 The Matrix.org Foundation C.I.C.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+type: object
+description: |-
+  The auth_events and prev_events fields of PDUs for room version 4
+  and beyond.
+properties:
+  auth_events:
+    type: array
+    items:
+      type: string
+      description: Event ID.
+    description: |-
+      Event IDs for the authorization events that would
+      allow this event to be in the room.
+
+      Must contain less than or equal to 10 events. Note that if the relevant
+      auth event selection rules are used, this restriction should never be
+      encountered.
+    example: ["$URLsafe-base64EncodedHash", "$Another_Event"]
+  prev_events:
+    type: array
+    items:
+      type: string
+      description: Event ID.
+    description: |-
+      Event IDs for the most recent events in the room
+      that the homeserver was aware of when it made this event.
+
+      Must contain less than or equal to 20 events.
+    example: ["$URLsafe-base64EncodedHash", "$Another_Event"]
+required:
+  - auth_events
+  - prev_events
diff --git a/data/api/server-server/definitions/event_hash.yaml b/data/api/server-server/definitions/components/event_hash.yaml
similarity index 100%
rename from data/api/server-server/definitions/event_hash.yaml
rename to data/api/server-server/definitions/components/event_hash.yaml
diff --git a/data/api/server-server/definitions/unsigned_pdu_base.yaml b/data/api/server-server/definitions/components/pdu_base.yaml
similarity index 63%
rename from data/api/server-server/definitions/unsigned_pdu_base.yaml
rename to data/api/server-server/definitions/components/pdu_base.yaml
index a2ec9552..4b676c8f 100644
--- a/data/api/server-server/definitions/unsigned_pdu_base.yaml
+++ b/data/api/server-server/definitions/components/pdu_base.yaml
@@ -12,10 +12,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 type: object
-title: Unsigned Persistent Data Unit
-description: An unsigned persistent data unit (event)
-example:
-  $ref: "../examples/unsigned_pdu_base.json"
+description: Common fields for all PDU versions
 properties:
   room_id:
     type: string
@@ -44,23 +41,6 @@ properties:
     type: object
     description: The content of the event.
     example: {"key": "value"}
-  prev_events:
-    type: array
-    description: |-
-      Event IDs and reference hashes for the most recent events in the room
-      that the homeserver was aware of when it made this event.
-
-      Must contain less than or equal to 20 events.
-    items:
-      type: array
-      maxItems: 2
-      minItems: 2
-      items:
-        anyOf:
-          - type: string
-            title: Event ID
-            example: "$abc123:matrix.org"
-          - $ref: "event_hash.yaml"
   depth:
     type: integer
     description: |-
@@ -68,25 +48,22 @@ properties:
       maximum value for an integer (2^63 - 1). If the room's depth is already at
       the limit, the depth must be set to the limit.
     example: 12
-  auth_events:
-    type: array
+  hashes:
+    $ref: "event_hash.yaml"
+  signatures:
+    type: object
     description: |-
-      Event IDs and reference hashes for the authorization events that would
-      allow this event to be in the room.
-
-      Must contain less than or equal to 10 events. Note that if the relevant
-      auth event selection rules are used, this restriction should never be
-      encountered.
-    items:
-      type: array
-      maxItems: 2
-      minItems: 2
-      items:
-        anyOf:
-          - type: string
-            title: Event ID
-            example: "$abc123:matrix.org"
-          - $ref: "event_hash.yaml"
+      Signatures for the PDU, following the algorithm specified in [Signing Events](/server-server-api/#signing-events).
+    example: {
+      "example.com": {
+        "ed25519:key_version:": "86BytesOfSignatureOfTheRedactedEvent"
+      }
+    }
+    additionalProperties:
+      type: object
+      title: Server Signatures
+      additionalProperties:
+        type: string
   unsigned:
     type: object
     title: UnsignedData
@@ -99,12 +76,11 @@ properties:
         description: The number of milliseconds that have passed since this message was sent.
         example: 4612
 required:
-  - event_id
   - room_id
   - sender
   - origin_server_ts
   - type
   - content
-  - prev_events
   - depth
-  - auth_events
+  - hashes
+  - signatures
diff --git a/data/api/server-server/definitions/pdu.yaml b/data/api/server-server/definitions/pdu.yaml
deleted file mode 100644
index 00b83321..00000000
--- a/data/api/server-server/definitions/pdu.yaml
+++ /dev/null
@@ -1,45 +0,0 @@
-# Copyright 2018 New Vector Ltd
-#
-# Licensed under the Apache License, Version 2.0 (the "License");
-# you may not use this file except in compliance with the License.
-# You may obtain a copy of the License at
-#
-#     http://www.apache.org/licenses/LICENSE-2.0
-#
-# Unless required by applicable law or agreed to in writing, software
-# distributed under the License is distributed on an "AS IS" BASIS,
-# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-# See the License for the specific language governing permissions and
-# limitations under the License.
-type: object
-title: Persistent Data Unit
-description: A persistent data unit (event) for room versions 1 and 2.
-example:
-  $ref: "../examples/pdu.json"
-allOf:
-  - $ref: "unsigned_pdu.yaml"
-  - type: object
-    properties:
-      redacts:
-        type: string
-        description: For redaction events, the ID of the event being redacted.
-        example: "$def456:matrix.org"
-      hashes:
-        $ref: "event_hash.yaml"
-      signatures:
-        type: object
-        description: |-
-          Signatures for the PDU, following the algorithm specified in [Signing Events](/server-server-api/#signing-events).
-        example: {
-          "example.com": {
-            "ed25519:key_version:": "86BytesOfSignatureOfTheRedactedEvent"
-          }
-        }
-        additionalProperties:
-          type: object
-          title: Server Signatures
-          additionalProperties:
-            type: string
-    required:
-      - hashes
-      - signatures
diff --git a/data/api/server-server/definitions/pdu_v1.yaml b/data/api/server-server/definitions/pdu_v1.yaml
new file mode 100644
index 00000000..b9ba8cc1
--- /dev/null
+++ b/data/api/server-server/definitions/pdu_v1.yaml
@@ -0,0 +1,70 @@
+# Copyright 2018 New Vector Ltd
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+type: object
+title: Persistent Data Unit
+description: A persistent data unit (event) for room versions 1 and 2.
+example:
+  $ref: "../examples/pdu_v1.json"
+allOf:
+  - $ref: "components/pdu_base.yaml"
+  - type: object
+    properties:
+      event_id:
+        type: string
+        description: The event ID for the PDU.
+        example: "$a4ecee13e2accdadf56c1025:example.com"
+      redacts:
+        type: string
+        description: For redaction events, the ID of the event being redacted.
+        example: "$def456:matrix.org"
+      auth_events:
+        type: array
+        description: |-
+          Event IDs and reference hashes for the authorization events that would
+          allow this event to be in the room.
+
+          Must contain less than or equal to 10 events. Note that if the relevant
+          auth event selection rules are used, this restriction should never be
+          encountered.
+        items:
+          type: array
+          maxItems: 2
+          minItems: 2
+          items:
+            anyOf:
+              - type: string
+                title: Event ID
+                example: "$abc123:matrix.org"
+              - $ref: "components/event_hash.yaml"
+      prev_events:
+        type: array
+        description: |-
+          Event IDs and reference hashes for the most recent events in the room
+          that the homeserver was aware of when it made this event.
+
+          Must contain less than or equal to 20 events.
+        items:
+          type: array
+          maxItems: 2
+          minItems: 2
+          items:
+            anyOf:
+              - type: string
+                title: Event ID
+                example: "$abc123:matrix.org"
+              - $ref: "components/event_hash.yaml"
+    required:
+      - event_id
+      - auth_events
+      - prev_events
diff --git a/data/api/server-server/definitions/pdu_v11.yaml b/data/api/server-server/definitions/pdu_v11.yaml
index 60f9b3ac..a3db6ee9 100644
--- a/data/api/server-server/definitions/pdu_v11.yaml
+++ b/data/api/server-server/definitions/pdu_v11.yaml
@@ -17,53 +17,6 @@ description: A persistent data unit (event) for room version 11 and beyond.
 example:
   $ref: "../examples/pdu_v11.json"
 allOf:
-  # v11 is the v4 event, but without redacts. Copy the auth_events/prev_events
-  # from pdu_v4.yaml and hashes and signatures from pdu_v3.yaml.
-  - $ref: "unsigned_pdu_base.yaml"
-  - type: object
-    properties:
-      auth_events:
-        type: array
-        items:
-          type: string
-          description: Event ID.
-        description: |-
-          Event IDs for the authorization events that would
-          allow this event to be in the room.
-
-          Must contain less than or equal to 10 events. Note that if the relevant
-          auth event selection rules are used, this restriction should never be
-          encountered.
-        example: ["$URLsafe-base64EncodedHash", "$Another_Event"]
-      prev_events:
-        type: array
-        items:
-          type: string
-          description: Event ID.
-        description: |-
-          Event IDs for the most recent events in the room
-          that the homeserver was aware of when it made this event.
-
-          Must contain less than or equal to 20 events.
-        example: ["$URLsafe-base64EncodedHash", "$Another_Event"]
-      hashes:
-        $ref: "event_hash.yaml"
-      signatures:
-        type: object
-        description: |-
-          Signatures for the PDU, following the algorithm specified in [Signing Events](/server-server-api/#signing-events).
-        example: {
-          "example.com": {
-            "ed25519:key_version:": "86BytesOfSignatureOfTheRedactedEvent"
-          }
-        }
-        additionalProperties:
-          type: object
-          title: Server Signatures
-          additionalProperties:
-            type: string
-    required:
-      - auth_events
-      - prev_events
-      - hashes
-      - signatures
+  # v11 is the v4 event, but without redacts.
+  - $ref: "components/pdu_base.yaml"
+  - $ref: "components/auth_events_prev_events_v4.yaml"
\ No newline at end of file
diff --git a/data/api/server-server/definitions/pdu_v3.yaml b/data/api/server-server/definitions/pdu_v3.yaml
index e801518c..69d8900c 100644
--- a/data/api/server-server/definitions/pdu_v3.yaml
+++ b/data/api/server-server/definitions/pdu_v3.yaml
@@ -13,11 +13,11 @@
 # limitations under the License.
 type: object
 title: Persistent Data Unit
-description: A persistent data unit (event) for room version 3 and beyond.
+description: A persistent data unit (event) for room version 3.
 example:
   $ref: "../examples/pdu_v3.json"
 allOf:
-  - $ref: "unsigned_pdu_base.yaml"
+  - $ref: "components/pdu_base.yaml"
   - type: object
     properties:
       redacts:
@@ -48,24 +48,6 @@ allOf:
 
           Must contain less than or equal to 20 events.
         example: ["$base64EncodedHash", "$AnotherEvent"]
-      hashes:
-        $ref: "event_hash.yaml"
-      signatures:
-        type: object
-        description: |-
-          Signatures for the PDU, following the algorithm specified in [Signing Events](/server-server-api/#signing-events).
-        example: {
-          "example.com": {
-            "ed25519:key_version:": "86BytesOfSignatureOfTheRedactedEvent"
-          }
-        }
-        additionalProperties:
-          type: object
-          title: Server Signatures
-          additionalProperties:
-            type: string
     required:
       - auth_events
       - prev_events
-      - hashes
-      - signatures
diff --git a/data/api/server-server/definitions/pdu_v4.yaml b/data/api/server-server/definitions/pdu_v4.yaml
index d22956c6..e859ee86 100644
--- a/data/api/server-server/definitions/pdu_v4.yaml
+++ b/data/api/server-server/definitions/pdu_v4.yaml
@@ -13,41 +13,16 @@
 # limitations under the License.
 type: object
 title: Persistent Data Unit
-description: A persistent data unit (event) for room version 4 and beyond.
+description: |-
+  A persistent data unit (event) for room versions 4, 5, 6, 7, 8, 9 and 10.
 example:
   $ref: "../examples/pdu_v4.json"
 allOf:
-  - $ref: "pdu_v3.yaml"
+  - $ref: "components/pdu_base.yaml"
+  - $ref: "components/auth_events_prev_events_v4.yaml"
   - type: object
     properties:
       redacts:
         type: string
         description: For redaction events, the ID of the event being redacted.
         example: "$def_456-oldevent"
-      auth_events:
-        type: array
-        items:
-          type: string
-          description: Event ID.
-        description: |-
-          Event IDs for the authorization events that would
-          allow this event to be in the room.
-
-          Must contain less than or equal to 10 events. Note that if the relevant
-          auth event selection rules are used, this restriction should never be
-          encountered.
-        example: ["$URLsafe-base64EncodedHash", "$Another_Event"]
-      prev_events:
-        type: array
-        items:
-          type: string
-          description: Event ID.
-        description: |-
-          Event IDs for the most recent events in the room
-          that the homeserver was aware of when it made this event.
-
-          Must contain less than or equal to 20 events.
-        example: ["$URLsafe-base64EncodedHash", "$Another_Event"]
-    required:
-      - auth_events
-      - prev_events
diff --git a/data/api/server-server/definitions/unsigned_pdu.yaml b/data/api/server-server/definitions/unsigned_pdu.yaml
deleted file mode 100644
index a27a21cd..00000000
--- a/data/api/server-server/definitions/unsigned_pdu.yaml
+++ /dev/null
@@ -1,28 +0,0 @@
-# Copyright 2018-2019 New Vector Ltd
-#
-# Licensed under the Apache License, Version 2.0 (the "License");
-# you may not use this file except in compliance with the License.
-# You may obtain a copy of the License at
-#
-#     http://www.apache.org/licenses/LICENSE-2.0
-#
-# Unless required by applicable law or agreed to in writing, software
-# distributed under the License is distributed on an "AS IS" BASIS,
-# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-# See the License for the specific language governing permissions and
-# limitations under the License.
-type: object
-title: Unsigned Persistent Data Unit
-description: An unsigned persistent data unit (event)
-example:
-  $ref: "../examples/unsigned_pdu.json"
-allOf:
-  - $ref: "unsigned_pdu_base.yaml"
-  - type: object
-    properties:
-      event_id:
-        type: string
-        description: The event ID for the PDU.
-        example: "$a4ecee13e2accdadf56c1025:example.com"
-    required:
-      - event_id
diff --git a/data/api/server-server/examples/components/auth_events_prev_events_v4.json b/data/api/server-server/examples/components/auth_events_prev_events_v4.json
new file mode 100644
index 00000000..3a203b49
--- /dev/null
+++ b/data/api/server-server/examples/components/auth_events_prev_events_v4.json
@@ -0,0 +1,10 @@
+{
+    "auth_events": [
+        "$urlsafe_base64_encoded_eventid",
+        "$a-different-event-id"
+    ],
+    "prev_events": [
+        "$urlsafe_base64_encoded_eventid",
+        "$a-different-event-id"
+    ]
+}
\ No newline at end of file
diff --git a/data/api/server-server/examples/components/pdu_base.json b/data/api/server-server/examples/components/pdu_base.json
new file mode 100644
index 00000000..448aeafa
--- /dev/null
+++ b/data/api/server-server/examples/components/pdu_base.json
@@ -0,0 +1,21 @@
+{
+    "room_id": "!UcYsUzyxTGDxLBEvLy:example.org",
+    "sender": "@alice:example.com",
+    "origin_server_ts": 1404838188000,
+    "depth": 12,
+    "type": "m.room.message",
+    "content": {
+        "key": "value"
+    },
+    "hashes": {
+        "sha256": "thishashcoversallfieldsincasethisisredacted"
+    },
+    "signatures": {
+        "example.com": {
+            "ed25519:key_version": "these86bytesofbase64signaturecoveressentialfieldsincludinghashessocancheckredactedpdus"
+        }
+    },
+    "unsigned": {
+        "age": 4612
+    }
+}
diff --git a/data/api/server-server/examples/pdu.json b/data/api/server-server/examples/pdu.json
deleted file mode 100644
index 81981b23..00000000
--- a/data/api/server-server/examples/pdu.json
+++ /dev/null
@@ -1,11 +0,0 @@
-{
-    "$ref": "unsigned_pdu.json",
-    "hashes": {
-        "sha256": "thishashcoversallfieldsincasethisisredacted"
-    },
-    "signatures": {
-        "example.com": {
-            "ed25519:key_version:": "these86bytesofbase64signaturecoveressentialfieldsincludinghashessocancheckredactedpdus"
-        }
-    }
-}
\ No newline at end of file
diff --git a/data/api/server-server/examples/unsigned_pdu_base.json b/data/api/server-server/examples/pdu_v1.json
similarity index 52%
rename from data/api/server-server/examples/unsigned_pdu_base.json
rename to data/api/server-server/examples/pdu_v1.json
index 079ee1ea..4e80ca52 100644
--- a/data/api/server-server/examples/unsigned_pdu_base.json
+++ b/data/api/server-server/examples/pdu_v1.json
@@ -1,25 +1,16 @@
 {
-    "room_id": "!UcYsUzyxTGDxLBEvLy:example.org",
-    "sender": "@alice:example.com",
-    "origin_server_ts": 1404838188000,
-    "depth": 12,
+    "$ref": "components/pdu_base.json",
+    "event_id": "$a4ecee13e2accdadf56c1025:example.com",
     "auth_events": [
         [
             "$af232176:example.org",
             {"sha256": "abase64encodedsha256hashshouldbe43byteslong"}
         ]
     ],
-    "type": "m.room.message",
     "prev_events": [
         [
             "$af232176:example.org",
             {"sha256": "abase64encodedsha256hashshouldbe43byteslong"}
         ]
-    ],
-    "content": {
-        "key": "value"
-    },
-    "unsigned": {
-        "age": 4612
-    }
-}
+    ]
+}
\ No newline at end of file
diff --git a/data/api/server-server/examples/pdu_v11.json b/data/api/server-server/examples/pdu_v11.json
index 292f38a0..bbdcf433 100644
--- a/data/api/server-server/examples/pdu_v11.json
+++ b/data/api/server-server/examples/pdu_v11.json
@@ -1,19 +1,6 @@
 {
-    "$ref": "unsigned_pdu_base.json",
-    "hashes": {
-        "sha256": "thishashcoversallfieldsincasethisisredacted"
-    },
-    "signatures": {
-        "example.com": {
-            "ed25519:key_version:": "these86bytesofbase64signaturecoveressentialfieldsincludinghashessocancheckredactedpdus"
-        }
-    },
-    "auth_events": [
-        "$urlsafe_base64_encoded_eventid",
-        "$a-different-event-id"
-    ],
-    "prev_events": [
-        "$urlsafe_base64_encoded_eventid",
-        "$a-different-event-id"
+    "allOf": [
+        { "$ref": "components/pdu_base.json" },
+        { "$ref": "components/auth_events_prev_events_v4.json" }
     ]
 }
diff --git a/data/api/server-server/examples/pdu_v3.json b/data/api/server-server/examples/pdu_v3.json
index acffdf26..6d2f5244 100644
--- a/data/api/server-server/examples/pdu_v3.json
+++ b/data/api/server-server/examples/pdu_v3.json
@@ -1,13 +1,5 @@
 {
-    "$ref": "unsigned_pdu_base.json",
-    "hashes": {
-        "sha256": "thishashcoversallfieldsincasethisisredacted"
-    },
-    "signatures": {
-        "example.com": {
-            "ed25519:key_version:": "these86bytesofbase64signaturecoveressentialfieldsincludinghashessocancheckredactedpdus"
-        }
-    },
+    "$ref": "components/pdu_base.json",
     "auth_events": [
         "$base64encodedeventid",
         "$adifferenteventid"
diff --git a/data/api/server-server/examples/pdu_v4.json b/data/api/server-server/examples/pdu_v4.json
index 3c2f0e22..ae25d537 100644
--- a/data/api/server-server/examples/pdu_v4.json
+++ b/data/api/server-server/examples/pdu_v4.json
@@ -1,12 +1,7 @@
 {
-    "$ref": "pdu_v3.json",
-    "auth_events": [
-        "$urlsafe_base64_encoded_eventid",
-        "$a-different-event-id"
-    ],
-    "prev_events": [
-        "$urlsafe_base64_encoded_eventid",
-        "$a-different-event-id"
-    ],
-    "redacts": "$some-old_event"
+    "allOf": [
+        { "$ref": "components/pdu_base.json" },
+        { "$ref": "components/auth_events_prev_events_v4.json" },
+        { "redacts": "$some-old_event" }
+    ]
 }
diff --git a/data/api/server-server/examples/pdu_v4_join_membership.json b/data/api/server-server/examples/pdu_v4_join_membership.json
index 1057ea94..23f69e81 100644
--- a/data/api/server-server/examples/pdu_v4_join_membership.json
+++ b/data/api/server-server/examples/pdu_v4_join_membership.json
@@ -1,8 +1,5 @@
 {
-    "$ref": "unsigned_pdu_base.json",
-    "hashes": {
-        "sha256": "thishashcoversallfieldsincasethisisredacted"
-    },
+    "$ref": "components/pdu_base.json",
     "signatures": {
         "example.com": {
             "ed25519:key_version": "these86bytesofbase64signaturecoveressentialfieldsincludinghashessocancheckredactedpdus"
diff --git a/data/api/server-server/examples/unsigned_pdu.json b/data/api/server-server/examples/unsigned_pdu.json
deleted file mode 100644
index b886a365..00000000
--- a/data/api/server-server/examples/unsigned_pdu.json
+++ /dev/null
@@ -1,4 +0,0 @@
-{
-    "$ref": "unsigned_pdu_base.json",
-    "event_id": "$a4ecee13e2accdadf56c1025:example.com"
-}