diff --git a/CHANGELOG.md b/CHANGELOG.md
index 6c2981618..aecc07b15 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -26,6 +26,8 @@ Inspired from [Keep a Changelog](https://keepachangelog.com/en/1.0.0/)
 - Added request body to `_search_shards` API specs ([#709](https://github.com/opensearch-project/opensearch-api-specification/pull/709))
 - Added NodeAttributes as additional property in `shard_stores` API specs ([#715](https://github.com/opensearch-project/opensearch-api-specification/pull/715))
 - Added missing `repository` query parameter to `/_cat/snapshots` ([#700](https://github.com/opensearch-project/opensearch-api-specification/pull/700))
+- Added `sm` namespace API specifications ([#701](https://github.com/opensearch-project/opensearch-api-specification/pull/701))
+- Added schema for `/_plugins/_knn/stats`, `/_plugins/_knn/models/{model_id}`, `_train` and `_search` ([#704](https://github.com/opensearch-project/opensearch-api-specification/pull/704))
 
 ### Removed
 - Removed unsupported `_common.mapping:SourceField`'s `mode` field and associated `_common.mapping:SourceFieldMode` enum ([#652](https://github.com/opensearch-project/opensearch-api-specification/pull/652))
@@ -167,7 +169,6 @@ Inspired from [Keep a Changelog](https://keepachangelog.com/en/1.0.0/)
 - Added API spec for `adjust_pure_negative` for bool queries ([#641](https://github.com/opensearch-project/opensearch-api-specification/pull/641))
 - Added a spec style checker [#620](https://github.com/opensearch-project/opensearch-api-specification/pull/620).
 - Added `remote_store` to node `Stats` ([#643](https://github.com/opensearch-project/opensearch-api-specification/pull/643))
-- Added `sm` namespace API specifications ([#701](https://github.com/opensearch-project/opensearch-api-specification/pull/701))
 
 ### Changed
 
diff --git a/spec/namespaces/knn.yaml b/spec/namespaces/knn.yaml
index 563f4f783..d7156d4b9 100644
--- a/spec/namespaces/knn.yaml
+++ b/spec/namespaces/knn.yaml
@@ -251,45 +251,28 @@ components:
       content:
         application/json:
           schema:
-            type: object
-            properties:
-              training_index:
-                type: string
-              training_field:
-                type: string
-              dimension:
-                type: integer
-                format: int32
-              max_training_vector_count:
-                type: integer
-                format: int32
-              search_size:
-                type: integer
-                format: int32
-              description:
-                type: string
-              mode:
-                type: string
-              compression_level:
-                type: string
-              method:
-                type: string
-              spaceType:
-                type: string
-            required:
-              - dimension
-              - training_field
-              - training_index
-      required: true
+            $ref: '../schemas/knn._common.yaml#/components/schemas/TrainedModel'
   responses:
-    knn.delete_model@200: {}
+    knn.delete_model@200:
+      content:
+        application/json:
+          schema:
+            $ref: '../schemas/knn._common.yaml#/components/schemas/DeletedModel'
     knn.get_model@200:
       content:
         application/json:
           schema:
             type: object
-    knn.search_models@200: {}
-    knn.stats@200: {}
+    knn.search_models@200:
+      content:
+        application/json:
+          schema:
+            $ref: '../schemas/_core.search.yaml#/components/schemas/ResponseBody'
+    knn.stats@200:
+      content:
+        application/json:
+          schema:
+            $ref: '../schemas/knn._common.yaml#/components/schemas/Stats'
     knn.train_model@200:
       content:
         application/json:
@@ -681,12 +664,19 @@ components:
             - graph_memory_usage_percentage
             - graph_query_errors
             - graph_query_requests
+            - graph_stats
             - hit_count
             - indexing_from_model_degraded
             - indices_in_cache
             - knn_query_requests
+            - knn_query_with_filter_requests
             - load_exception_count
             - load_success_count
+            - lucene_initialized
+            - max_distance_query_requests
+            - max_distance_query_with_filter_requests
+            - min_score_query_requests
+            - min_score_query_with_filter_requests
             - miss_count
             - model_index_status
             - nmslib_initialized
diff --git a/spec/schemas/knn._common.yaml b/spec/schemas/knn._common.yaml
index b4cbeaa36..6a71753ae 100644
--- a/spec/schemas/knn._common.yaml
+++ b/spec/schemas/knn._common.yaml
@@ -25,3 +25,164 @@ components:
         - always
         - missing
         - popular
+    Stats:
+      type: object
+      properties:
+        _nodes:
+          $ref: '_common.yaml#/components/schemas/NodeStatistics'
+        cluster_name:
+          $ref: '_common.yaml#/components/schemas/Name'
+        circuit_breaker_triggered:
+          type: boolean
+        model_index_status:
+          oneOf:
+            - $ref: '_common.yaml#/components/schemas/HealthStatusCapitalized'
+            - type: 'null'
+        nodes:
+          type: object
+          additionalProperties:
+            $ref: '#/components/schemas/NodeStats'
+    NodeStats:
+      type: object
+      properties:
+        max_distance_query_with_filter_requests:
+          type: number
+        graph_memory_usage_percentage:
+          $ref: '_common.yaml#/components/schemas/PercentageNumber'
+        graph_query_requests:
+          type: number
+        graph_memory_usage:
+          type: number
+        cache_capacity_reached:
+          type: boolean
+        load_success_count:
+          type: number
+        training_memory_usage:
+          type: number
+        indices_in_cache:
+          type: object
+          additionalProperties: true
+        script_query_errors:
+          type: number
+        hit_count:
+          type: number
+        knn_query_requests:
+          type: number
+        total_load_time:
+          type: number
+        miss_count:
+          type: number
+        min_score_query_requests:
+          type: number
+        knn_query_with_filter_requests:
+          type: number
+        training_memory_usage_percentage:
+          $ref: '_common.yaml#/components/schemas/PercentageNumber'
+        max_distance_query_requests:
+          type: number
+        lucene_initialized:
+          type: boolean
+        graph_index_requests:
+          type: number
+        faiss_initialized:
+          type: boolean
+        load_exception_count:
+          type: number
+        training_errors:
+          type: number
+        min_score_query_with_filter_requests:
+          type: number
+        eviction_count:
+          type: number
+        nmslib_initialized:
+          type: boolean
+        script_compilations:
+          type: number
+        script_query_requests:
+          type: number
+        graph_stats:
+          $ref: '#/components/schemas/GraphStats'
+        graph_query_errors:
+          type: number
+        indexing_from_model_degraded:
+          type: boolean
+        graph_index_errors:
+          type: number
+        training_requests:
+          type: number
+        script_compilation_errors:
+          type: number
+    GraphStats:
+      type: object
+      properties:
+        merge:
+          $ref: '#/components/schemas/GraphMergeStats'
+        refresh:
+          $ref: '#/components/schemas/GraphRefreshStats'
+    GraphRefreshStats:
+      type: object
+      properties:
+        total:
+          type: number
+        total_time_in_millis:
+          $ref: '_common.yaml#/components/schemas/DurationValueUnitMillis'
+    GraphMergeStats:
+      type: object
+      properties:
+        current:
+          type: number
+        total:
+          type: number
+        total_time_in_millis:
+          $ref: '_common.yaml#/components/schemas/DurationValueUnitMillis'
+        current_docs:
+          type: number
+        total_docs:
+          type: number
+        total_size_in_bytes:
+          $ref: '_common.yaml#/components/schemas/ByteCount'
+        current_size_in_bytes:
+          $ref: '_common.yaml#/components/schemas/ByteCount'
+    TrainedModel:
+      type: object
+      properties:
+        training_index:
+          type: string
+        training_field:
+          type: string
+        dimension:
+          type: integer
+          format: int32
+        max_training_vector_count:
+          type: integer
+          format: int32
+        search_size:
+          type: integer
+          format: int32
+        description:
+          type: string
+        mode:
+          type: string
+        compression_level:
+          type: string
+        method:
+          type: string
+        spaceType:
+          type: string
+      required:
+        - dimension
+        - training_field
+        - training_index
+    DeletedModel:
+      type: object
+      properties:
+        model_id:
+          type: string
+        result:
+          type: string
+          enum:
+            - deleted
+            - error
+      required:
+        - model_id
+        - result
diff --git a/tests/default/knn/models.yaml b/tests/default/knn/models.yaml
new file mode 100644
index 000000000..3589fc162
--- /dev/null
+++ b/tests/default/knn/models.yaml
@@ -0,0 +1,61 @@
+$schema: ../../../json_schemas/test_story.schema.yaml
+
+description: Delete a k-NN model.
+version: '>= 2.17'
+prologues:
+  - method: PUT
+    path: /movies
+    request:
+      payload:
+        settings:
+          index:
+            knn: true
+        mappings:
+          properties:
+            recommendation_vector:
+              type: knn_vector
+              dimension: 8
+    status: [200]
+  - method: POST
+    path: /_bulk
+    parameters:
+      refresh: true
+    request:
+      content_type: application/x-ndjson
+      payload:
+        - {index: {_index: movies, _id: '1'}}
+        - {recommendation_vector: [1.5, 1.5, 1.5, 1.5, 1.5, 1.5, 1.5, 1.5], duration: 12.2}
+        - {index: {_index: movies, _id: '2'}}
+        - {recommendation_vector: [2.5, 2.5, 2.5, 2.5, 2.5, 2.5, 2.5, 2.5], duration: 7.1}
+    status: [200]
+  - method: POST
+    path: /_plugins/_knn/models/model-1/_train
+    request:
+      payload:
+        training_index: movies
+        training_field: recommendation_vector
+        dimension: 8
+        max_training_vector_count: 1200
+        search_size: 100
+        description: Test model
+        mode: on_disk
+        compression_level: 32x
+        spaceType: l2
+    status: [200]
+epilogues:
+  - path: /movies
+    method: DELETE
+    status: [200, 404]
+  - path: /_plugins/_knn/models/model-1
+    method: DELETE
+    status: [200, 404]
+chapters:
+  - synopsis: Delete a trained model.
+    method: DELETE  
+    path: /_plugins/_knn/models/{model_id}
+    parameters:
+      model_id: model-1
+    retry:
+      count: 3
+    response:
+      status: 200
diff --git a/tests/default/knn/models/search.yaml b/tests/default/knn/models/search.yaml
new file mode 100644
index 000000000..52711b0f5
--- /dev/null
+++ b/tests/default/knn/models/search.yaml
@@ -0,0 +1,70 @@
+$schema: ../../../../json_schemas/test_story.schema.yaml
+
+description: Search for a k-NN model.
+version: '>= 2.17'
+prologues:
+  - method: PUT
+    path: /movies
+    request:
+      payload:
+        settings:
+          index:
+            knn: true
+        mappings:
+          properties:
+            recommendation_vector:
+              type: knn_vector
+              dimension: 8
+    status: [200]
+  - method: POST
+    path: /_bulk
+    parameters:
+      refresh: true
+    request:
+      content_type: application/x-ndjson
+      payload:
+        - {index: {_index: movies, _id: '1'}}
+        - {recommendation_vector: [1.5, 1.5, 1.5, 1.5, 1.5, 1.5, 1.5, 1.5], duration: 12.2}
+        - {index: {_index: movies, _id: '2'}}
+        - {recommendation_vector: [2.5, 2.5, 2.5, 2.5, 2.5, 2.5, 2.5, 2.5], duration: 7.1}
+    status: [200]
+  - method: POST
+    path: /_plugins/_knn/models/model-1/_train
+    request:
+      payload:
+        training_index: movies
+        training_field: recommendation_vector
+        dimension: 8
+        max_training_vector_count: 1200
+        search_size: 100
+        description: Test model
+        mode: on_disk
+        compression_level: 32x
+        spaceType: l2
+    status: [200]
+epilogues:
+  - path: /movies
+    method: DELETE
+    status: [200, 404]
+  - path: /_plugins/_knn/models/model-1
+    method: DELETE
+    status: [200, 404]
+chapters:
+  - synopsis: Search models (GET).
+    method: GET
+    path: /_plugins/_knn/models/_search
+    request:
+      payload:
+        query:
+          match_all: {}
+    response:
+      status: 200
+  - synopsis: Search models (POST).
+    method: POST
+    path: /_plugins/_knn/models/_search
+    request:
+      payload:
+        query:
+          match_all: {}
+    response:
+      status: 200
diff --git a/tests/default/knn/train_model.yaml b/tests/default/knn/models/train.yaml
similarity index 77%
rename from tests/default/knn/train_model.yaml
rename to tests/default/knn/models/train.yaml
index cb58ed97c..fbcfb19d5 100644
--- a/tests/default/knn/train_model.yaml
+++ b/tests/default/knn/models/train.yaml
@@ -1,8 +1,7 @@
-$schema: ../../../json_schemas/test_story.schema.yaml
+$schema: ../../../../json_schemas/test_story.schema.yaml
 
-description: Test training k-NN model with disk-based parameters.
+description: Train a k-NN model with disk-based parameters.
 version: '>= 2.17'
-
 prologues:
   - method: PUT
     path: /movies
@@ -19,6 +18,8 @@ prologues:
     status: [200]
   - method: POST
     path: /_bulk
+    parameters:
+      refresh: true
     request:
       content_type: application/x-ndjson
       payload:
@@ -41,9 +42,6 @@ prologues:
         - {index: {_index: movies, _id: '9'}}
         - {recommendation_vector: [9.5, 9.5, 9.5, 9.5, 9.5, 9.5, 9.5, 9.5], duration: 8.9}
     status: [200]
-  - method: POST
-    path: /_refresh
-    status: [200]
 epilogues:
   - path: /movies
     method: DELETE
@@ -53,9 +51,11 @@ epilogues:
       model_id: ${train_model.test_model_id}
     method: DELETE
     status: [200, 404]
-
+  - path: /_plugins/_knn/models/model-1
+    method: DELETE
+    status: [200, 404]
 chapters:
-  - synopsis: Test training a model with disk-based parameters.
+  - synopsis: Train a new model with disk-based parameters.
     id: train_model
     method: POST
     path: /_plugins/_knn/models/_train
@@ -88,3 +88,21 @@ chapters:
       payload:
         model_id: ${train_model.test_model_id}
         state: created
+  - synopsis: Train a model with a given ID.
+    method: POST
+    path: /_plugins/_knn/models/{model_id}/_train
+    parameters:
+      model_id: model-1
+    request:
+      payload:
+        training_index: movies
+        training_field: recommendation_vector
+        dimension: 8
+        max_training_vector_count: 2400
+        search_size: 100
+        description: Test model
+        mode: on_disk
+        compression_level: 32x
+        spaceType: l2
+    response:
+      status: 200
diff --git a/tests/default/knn/stats.yaml b/tests/default/knn/stats.yaml
new file mode 100644
index 000000000..f1fb9c5c9
--- /dev/null
+++ b/tests/default/knn/stats.yaml
@@ -0,0 +1,35 @@
+$schema: ../../../json_schemas/test_story.schema.yaml
+
+description: Get k-NN stats.
+chapters:
+  - synopsis: Get k-NN stats.
+    method: GET
+    path: /_plugins/_knn/stats
+    response:
+      status: 200
+  - synopsis: Get k-NN stat.
+    method: GET
+    path: /_plugins/_knn/stats/{stat}
+    parameters:
+      stat:
+        - hit_count
+    response:
+      status: 200
+  - synopsis: Get all k-NN stat for all nodes.
+    method: GET
+    path: /_plugins/_knn/{node_id}/stats
+    parameters:
+      node_id:
+        - _all
+    response:
+      status: 200
+  - synopsis: Get `hit_count` k-NN stat for all nodes.
+    method: GET
+    path: /_plugins/_knn/{node_id}/stats/{stat}
+    parameters:
+      node_id:
+        - _all
+      stat:
+        - hit_count
+    response:
+      status: 200