diff --git a/apis/eventstream/index.yaml b/apis/eventstream/index.yaml
index b0b0f748..621a8cf8 100644
--- a/apis/eventstream/index.yaml
+++ b/apis/eventstream/index.yaml
@@ -29,6 +29,7 @@ get:
             - finalized_checkpoint
             - chain_reorg
             - contribution_and_proof
+            - lightclient_head_update
   responses:
     "200":
       description: Opened SSE stream.
@@ -73,6 +74,18 @@ get:
               value: |
                 event: contribution_and_proof
                 data: {"message": {"aggregator_index": "997", "contribution": {"slot": "168097", "beacon_block_root": "0x56f1fd4262c08fa81e27621c370e187e621a67fc80fe42340b07519f84b42ea1", "subcommittee_index": "0", "aggregation_bits": "0xffffffffffffffffffffffffffffffff", "signature": "0x85ab9018e14963026476fdf784cc674da144b3dbdb47516185438768774f077d882087b90ad642469902e782a8b43eed0cfc1b862aa9a473b54c98d860424a702297b4b648f3f30bdaae8a8b7627d10d04cb96a2cc8376af3e54a9aa0c8145e3"}, "selection_proof": "0x87c305f04bfe5db27c2b19fc23e00d7ac496ec7d3e759cbfdd1035cb8cf6caaa17a36a95a08ba78c282725e7b66a76820ca4eb333822bd399ceeb9807a0f2926c67ce67cfe06a0b0006838203b493505a8457eb79913ce1a3bcd1cc8e4ef30ed"}, "signature": "0xac118511474a94f857300b315c50585c32a713e4452e26a6bb98cdb619936370f126ed3b6bb64469259ee92e69791d9e12d324ce6fd90081680ce72f39d85d50b0ff977260a8667465e613362c6d6e6e745e1f9323ec1d6f16041c4e358839ac"}
+            lightclient_head_update:
+              description: |
+                The node has received or constructed a new or better SyncAggregate for a header. `header` is the block header signed by `sync_aggregate`.
+                Nodes should track the participation of emitted updates per header and only emit updates if `new_participation > prev_participation + 16`.
+                Updates may be collected via:
+                - Next block's syncAggregate field
+                - Aggregating messages from gossip topic `sync_committee_contribution_and_proof`
+                - Aggregating messages from gossip topics `sync_committee_{subnet_id}`
+                Nodes may throttle emitting updates for a same header, but must emit the best update available eventually.
+              value: |
+                event: lightclient_head_update
+                data: {"message": {"sync_aggregate": {"sync_committee_bits": "0xfffffffffbfffffffffffffffffffffffffffffffffffffffffffefffffffffffffffffffffffeffffffffffeffffffffffffffffffffdffffffffffffffffff", "sync_committee_signature": "0x8a5e838431917331c461f38ec0f6c0b2f29c6cd2c9c9b7ed970b4700a8bc66bdb4b11ca129dd9c72fc1bbb1959c4a7cc0a0d8d107267f3cc364951747ad5ddd757555358e5910cec387179996a6e698d813df723ae02a825b6034af062913b91"}, "attested_header": {"slot": "2642381", "proposer_index": "189806", "parent_root": "0xa00016e7462de60629c9b81b10d1f79c29ae43d81972a3c0e1e92801e3599d9d", "state_root": "0xaec6a955ff0ff9c0081828bad99342b3e60c4744a65e8c7ef1fd01bb1162b4ca", "body_root": "0xeed126eddef983e1270cf72bea05f62195590576a7472a6ae1b43a7bd1aa6f23"}}}
     "400":
       description: "The topics supplied could not be parsed"
       content:
@@ -84,5 +97,4 @@ get:
                   code: 400
                   message: "Invalid topic: weather_forecast"
     "500":
-      $ref: '../../beacon-node-oapi.yaml#/components/responses/InternalError'
-      
+      $ref: "../../beacon-node-oapi.yaml#/components/responses/InternalError"
diff --git a/apis/lightclient/committee_updates.yaml b/apis/lightclient/committee_updates.yaml
new file mode 100644
index 00000000..c3163400
--- /dev/null
+++ b/apis/lightclient/committee_updates.yaml
@@ -0,0 +1,41 @@
+get:
+  operationId: getCommitteeUpdates
+  summary: Get committee updates in an inclusive range of sync periods
+  description: |
+    Returns an array of best updates in the requested periods within the inclusive range `from` - `to`.
+    Best is defined by (in order of priority):
+    - Is finalized update + > 2/3 participations
+    - Highest participation (bit count)
+    - Oldest update
+    Tracks oldest instead of newest to reduce disk writes and the likelihood of re-orgs. Clients may choose
+    a different set of "best" criteria if necessary.
+  tags:
+    - Lightclient
+  parameters:
+    - name: from
+      in: query
+      required: true
+      description: "Sync period start of requested range"
+      schema:
+        $ref: "../../beacon-node-oapi.yaml#/components/schemas/Uint64"
+    - name: to
+      in: query
+      required: true
+      description: "Sync period end of requested range (inclusive)"
+      schema:
+        $ref: "../../beacon-node-oapi.yaml#/components/schemas/Uint64"
+  responses:
+    "200":
+      description: Success
+      content:
+        application/json:
+          schema:
+            title: GetCommitteeUpdatesResponse
+            type: object
+            properties:
+              data:
+                type: array
+                items:
+                  $ref: "../../beacon-node-oapi.yaml#/components/schemas/LightClientUpdate"
+    "500":
+      $ref: "../../beacon-node-oapi.yaml#/components/responses/InternalError"
diff --git a/apis/lightclient/head_update.yaml b/apis/lightclient/head_update.yaml
new file mode 100644
index 00000000..f5b0b2fa
--- /dev/null
+++ b/apis/lightclient/head_update.yaml
@@ -0,0 +1,22 @@
+get:
+  operationId: getHeadUpdate
+  summary: Get latest best head update
+  description: |
+    Returns the latest best head update available. Clients should use the events endpoint and subscribe
+    to `lightclient_head_update` unless to get the very first head update after syncing, or if the events
+    endpoint is not supported by the server.
+  tags:
+    - Lightclient
+  responses:
+    "200":
+      description: Success
+      content:
+        application/json:
+          schema:
+            title: GetHeadUpdateResponse
+            type: object
+            properties:
+              data:
+                $ref: "../../beacon-node-oapi.yaml#/components/schemas/LightclientHeadUpdate"
+    "500":
+      $ref: "../../beacon-node-oapi.yaml#/components/responses/InternalError"
diff --git a/apis/lightclient/snapshot.yaml b/apis/lightclient/snapshot.yaml
new file mode 100644
index 00000000..97b87b61
--- /dev/null
+++ b/apis/lightclient/snapshot.yaml
@@ -0,0 +1,49 @@
+get:
+  operationId: getSnapshot
+  summary: Fetch a snapshot with a proof to a trusted block root.
+  description: |
+    Fetch a snapshot with a proof to a trusted block root.
+    The trusted block root should be fetched with similar means to a weak subjectivity checkpoint.
+    Only block roots for checkpoints within the weak subjectivity period must be guaranteed to be available.
+    If the node started with a recent weak subjectivity checkpoint, the node may not backfill snapshots
+    for older checkpoints.
+  tags:
+    - Lightclient
+  parameters:
+    - name: block_root
+      in: path
+      required: true
+      $ref: "../../beacon-node-oapi.yaml#/components/schemas/Root"
+  responses:
+    "200":
+      description: Success
+      content:
+        application/json:
+          schema:
+            title: GetSnapshotResponse
+            type: object
+            properties:
+              data:
+                $ref: "../../beacon-node-oapi.yaml#/components/schemas/LightclientSnapshot"
+    "400":
+      description: "Invalid block root"
+      content:
+        application/json:
+          schema:
+            allOf:
+              - $ref: "../../beacon-node-oapi.yaml#/components/schemas/ErrorMessage"
+              - example:
+                  code: 400
+                  message: "Invalid block root: head"
+    "404":
+      description: "Snapshot not found"
+      content:
+        application/json:
+          schema:
+            allOf:
+              - $ref: "../../beacon-node-oapi.yaml#/components/schemas/ErrorMessage"
+              - example:
+                  code: 404
+                  message: "Snapshot not found for block root"
+    "500":
+      $ref: "../../beacon-node-oapi.yaml#/components/responses/InternalError"
diff --git a/beacon-node-oapi.yaml b/beacon-node-oapi.yaml
index 3de5d220..aedb4fae 100644
--- a/beacon-node-oapi.yaml
+++ b/beacon-node-oapi.yaml
@@ -34,6 +34,8 @@ tags:
     description: Set of endpoints to debug chain and shouldn't be exposed publicly.
   - name: Events
     description: Set of endpoints to for event subscription.
+  - name: Lightclient
+    description: Endpoints to support server-based lightclients
   - name: Node
     description: Endpoints to query node related informations
   - name: Validator
@@ -96,6 +98,15 @@ paths:
   /eth/v1/debug/beacon/heads:
     $ref: './apis/debug/heads.yaml'
 
+  /eth/v1/lightclient/committee_updates:
+    $ref: "./apis/lightclient/committee_updates.yaml"
+  /eth/v1/lightclient/head_update:
+    $ref: "./apis/lightclient/head_update.yaml"
+  /eth/v1/lightclient/proof/{state_id}:
+    $ref: "./apis/lightclient/proof.yaml"
+  /eth/v1/lightclient/snapshot/{block_root}:
+    $ref: "./apis/lightclient/snapshot.yaml"
+
   /eth/v1/node/identity:
     $ref: "./apis/node/identity.yaml"
   /eth/v1/node/peers:
@@ -237,6 +248,12 @@ components:
       $ref: './types/altair/sync_committee.yaml#/Altair/SyncCommitteeContribution'
     Altair.SyncCommittee:
       $ref: './types/altair/sync_committee.yaml#/Altair/SyncCommitteeByValidatorIndices'
+    LightClientUpdate:
+      $ref: './types/altair/lightclient.yaml#/Altair/LightClientUpdate'
+    LightclientHeadUpdate:
+      $ref: './types/altair/lightclient.yaml#/Altair/LightclientHeadUpdate'
+    LightclientSnapshot:
+      $ref: './types/altair/lightclient.yaml#/Altair/LightclientSnapshot'
 
   parameters:
     StateId:
diff --git a/types/altair/lightclient.yaml b/types/altair/lightclient.yaml
new file mode 100644
index 00000000..c696260a
--- /dev/null
+++ b/types/altair/lightclient.yaml
@@ -0,0 +1,54 @@
+Altair:
+  LightClientUpdate:
+    type: object
+    properties:
+      attestedHeader:
+        $ref: '../block.yaml#/BeaconBlockHeader'
+      nextSyncCommittee:
+        $ref: './sync_committee.yaml#/Altair/SyncCommittee'
+      nextSyncCommitteeBranch:
+        $ref: '#/Altair/SyncCommitteeBranch'
+      finalizedHeader:
+        $ref: '../block.yaml#/BeaconBlockHeader'
+      finalityBranch:
+        $ref: '#/Altair/FinalityBranch'
+      syncAggregate:
+        $ref: './sync_aggregate.yaml#/Altair/SyncAggregate'
+      forkVersion:
+        $ref: '../primitive.yaml#/ForkVersion'
+  
+  FinalityBranch:
+    type: array
+    description: "Branch to state.finalized_checkpoint.root"
+    items:
+      allOf:
+        - $ref: '../primitive.yaml#/Root'
+    minItems: 6
+    maxItems: 6
+
+  SyncCommitteeBranch:
+    type: array
+    description: "Branch to state.next_sync_committee or state.current_sync_committee"
+    items:
+      allOf:
+        - $ref: '../primitive.yaml#/Root'
+    minItems: 5
+    maxItems: 5
+  
+  LightclientHeadUpdate:
+    type: object
+    properties:
+      attestedHeader:
+        $ref: '../block.yaml#/BeaconBlockHeader'
+      syncAggregate:
+        $ref: './sync_aggregate.yaml#/SyncAggregate'
+
+  LightclientSnapshot:
+    type: object
+    properties:
+      header:
+        $ref: '../block.yaml#/BeaconBlockHeader'
+      currentSyncCommittee:
+        $ref: './sync_committee.yaml#/Altair/SyncCommittee'
+      currentSyncCommitteeBranch:
+        $ref: '#/Altair/SyncCommitteeBranch'
diff --git a/types/altair/sync_aggregate.yaml b/types/altair/sync_aggregate.yaml
index db534ba5..44ac96fd 100644
--- a/types/altair/sync_aggregate.yaml
+++ b/types/altair/sync_aggregate.yaml
@@ -4,9 +4,11 @@ Altair:
     description: "The [`SyncAggregate`](https://github.com/ethereum/eth2.0-specs/blob/v1.1.0-alpha.1/specs/altair/beacon-chain.md#syncaggregate) object from the Eth2.0 Altair spec."
     properties:
       sync_committee_bits:
-        type: string
-        pattern: "^0x[a-fA-F0-9]+$"
-        example: "0x01"
-        description: "Aggregation bits of sync"
+        $ref: '#/Altair/SyncCommitteeBits'
       sync_committee_signature:
         $ref: '../primitive.yaml#/Signature'
+  SyncCommitteeBits:
+    allOf:
+      - description: 'A bit is set if a signature from the validator at the corresponding index in the subcommittee is present in the aggregate `signature`.'
+      - $ref: "../primitive.yaml#/Hex"
+      - example: "0x01"
diff --git a/types/altair/sync_committee.yaml b/types/altair/sync_committee.yaml
index 1ccee2f8..2bc77d2a 100644
--- a/types/altair/sync_committee.yaml
+++ b/types/altair/sync_committee.yaml
@@ -73,10 +73,7 @@ Altair:
           - $ref: '../primitive.yaml#/Uint64'
           - description: 'The index of the subcommittee that the contribution pertains to.'
       aggregation_bits:
-        allOf:
-          - description: 'A bit is set if a signature from the validator at the corresponding index in the subcommittee is present in the aggregate `signature`.'
-          - $ref: "../primitive.yaml#/Hex"
-          - example: "0x01"
+        $ref: './sync_aggregate.yaml#/Altair/SyncCommitteeBits'
       signature:
         allOf:
           - $ref: '../primitive.yaml#/Signature'
@@ -99,4 +96,3 @@ Altair:
           allOf:
             - $ref: '#/Altair/ValidatorsByIndex'
             - description: 'Subcommittee slices of the current sync committee'
-