New `vector_rescore` parameter as a quantized index type option (#124581)

This adds a new parameter to the quantized index mapping that allows
default oversampling and rescoring to occur. 

This doesn't adjust any of the defaults. It allows it to be configured.
When the user provides `rescore_vector: {oversample: <number>}` in the
query it will overwrite it.

For example, here is how to use it with bbq:

```
PUT rescored_bbq
{
  "mappings": {
    "properties": {
      "vector": {
        "type": "dense_vector",
        "index_options": {
          "type": "bbq_hnsw",
          "rescore_vector": {"oversample": 3.0}
        }
      }
    }
  }
}
```

Then, when querying, it will auto oversample the `k` by `3x` and rerank
with the raw vectors.

```
POST _search
{
  "knn": {
    "query_vector": [...],
    "field": "vector"
  }
}
```

docs/changelog/124581.yaml

@@ -0,0 +1,5 @@
+pr: 124581
+summary: New `vector_rescore` parameter as a quantized index type option
+area: Vector Search
+type: enhancement
+issues: []

docs/reference/elasticsearch/mapping-reference/dense-vector.md

@@ -287,6 +287,14 @@ $$$dense-vector-index-options$$$
     `confidence_interval`
     :   (Optional, float) Only applicable to `int8_hnsw`, `int4_hnsw`, `int8_flat`, and `int4_flat` index types. The confidence interval to use when quantizing the vectors. Can be any value between and including `0.90` and `1.0` or exactly `0`. When the value is `0`, this indicates that dynamic quantiles should be calculated for optimized quantization. When between `0.90` and `1.0`, this value restricts the values used when calculating the quantization thresholds. For example, a value of `0.95` will only use the middle 95% of the values when calculating the quantization thresholds (e.g. the highest and lowest 2.5% of values will be ignored). Defaults to `1/(dims + 1)` for `int8` quantized vectors and `0` for `int4` for dynamic quantile calculation.
 
+    `rescore_vector`
+    :   (Optional, object) Functionality in [preview]. An optional section that configures automatic vector rescoring on knn queries for the given field. Only applicable to quantized index types.
+    :::::{dropdown} Properties of `rescore_vector`
+    `oversample`
+    :   (required, float) The amount to oversample the search results by. This value should be greater than `1.0` and less than `10.0`. The higher the value, the more vectors will be gathered and rescored with the raw values per shard.
+        :   In case a knn query specifies a `rescore_vector` parameter, the query `rescore_vector` parameter will be used instead.
+        :   See [oversampling and rescoring quantized vectors](docs-content://solutions/search/vector/knn.md#dense-vector-knn-search-rescoring) for details.
+        :::::
     ::::
 
 

rest-api-spec/src/yamlRestTest/resources/rest-api-spec/test/search.vectors/41_knn_search_bbq_hnsw.yml

@@ -244,3 +244,93 @@ setup:
         index: dynamic_dim_bbq_hnsw
         body:
           vector: [1.0, 2.0, 3.0, 4.0, 1.0, 2.0, 3.0, 4.0, 1.0, 2.0, 3.0, 4.0, 1.0, 2.0, 3.0, 4.0, 1.0, 2.0, 3.0, 4.0, 1.0, 2.0, 3.0, 4.0, 1.0, 2.0, 3.0, 4.0, 1.0, 2.0, 3.0, 4.0, 1.0, 2.0, 3.0, 4.0, 1.0, 2.0, 3.0, 4.0, 1.0, 2.0, 3.0, 4.0, 1.0, 2.0, 3.0, 4.0, 1.0, 2.0, 3.0, 4.0, 1.0, 2.0, 3.0, 4.0, 1.0, 2.0, 3.0, 4.0, 1.0, 2.0, 3.0, 4.0]
+---
+"Test index configured rescore vector":
+  - requires:
+      cluster_features: ["mapper.dense_vector.rescore_vector"]
+      reason: Needs rescore_vector feature
+  - skip:
+      features: "headers"
+  - do:
+      indices.create:
+        index: bbq_rescore_hnsw
+        body:
+          settings:
+            index:
+              number_of_shards: 1
+          mappings:
+            properties:
+              vector:
+                type: dense_vector
+                dims: 64
+                index: true
+                similarity: max_inner_product
+                index_options:
+                  type: bbq_hnsw
+                  rescore_vector:
+                    oversample: 1.5
+
+  - do:
+      bulk:
+        index: bbq_rescore_hnsw
+        refresh: true
+        body: |
+          { "index": {"_id": "1"}}
+          { "vector": [0.077,  0.32 , -0.205,  0.63 ,  0.032,  0.201,  0.167, -0.313, 0.176,  0.531, -0.375,  0.334, -0.046,  0.078, -0.349,  0.272, 0.307, -0.083,  0.504,  0.255, -0.404,  0.289, -0.226, -0.132, -0.216,  0.49 ,  0.039,  0.507, -0.307,  0.107,  0.09 , -0.265, -0.285,  0.336, -0.272,  0.369, -0.282,  0.086, -0.132,  0.475, -0.224,  0.203,  0.439,  0.064,  0.246, -0.396,  0.297,  0.242, -0.028,  0.321, -0.022, -0.009, -0.001  ,  0.031, -0.533,  0.45, -0.683,  1.331,  0.194, -0.157, -0.1  , -0.279, -0.098, -0.176] }
+          { "index": {"_id": "2"}}
+          { "vector": [0.196,  0.514,  0.039,  0.555, -0.042,  0.242,  0.463, -0.348, -0.08 ,  0.442, -0.067, -0.05 , -0.001,  0.298, -0.377,  0.048, 0.307,  0.159,  0.278,  0.119, -0.057,  0.333, -0.289, -0.438, -0.014,  0.361, -0.169,  0.292, -0.229,  0.123,  0.031, -0.138, -0.139,  0.315, -0.216,  0.322, -0.445, -0.059,  0.071,  0.429, -0.602, -0.142,  0.11 ,  0.192,  0.259, -0.241,  0.181, -0.166, 0.082,  0.107, -0.05 ,  0.155,  0.011,  0.161, -0.486,  0.569, -0.489,  0.901,  0.208,  0.011, -0.209, -0.153, -0.27 , -0.013] }
+          { "index": {"_id": "3"}}
+          { "vector": [0.196,  0.514,  0.039,  0.555, -0.042,  0.242,  0.463, -0.348, -0.08 ,  0.442, -0.067, -0.05 , -0.001,  0.298, -0.377,  0.048, 0.307,  0.159,  0.278,  0.119, -0.057,  0.333, -0.289, -0.438, -0.014,  0.361, -0.169,  0.292, -0.229,  0.123,  0.031, -0.138, -0.139,  0.315, -0.216,  0.322, -0.445, -0.059,  0.071,  0.429, -0.602, -0.142,  0.11 ,  0.192,  0.259, -0.241,  0.181, -0.166, 0.082,  0.107, -0.05 ,  0.155,  0.011,  0.161, -0.486,  0.569, -0.489,  0.901,  0.208,  0.011, -0.209, -0.153, -0.27 , -0.013] }
+
+  - do:
+      headers:
+        Content-Type: application/json
+      search:
+        rest_total_hits_as_int: true
+        index: bbq_rescore_hnsw
+        body:
+          knn:
+            field: vector
+            query_vector: [0.128,  0.067, -0.08 ,  0.395, -0.11 , -0.259,  0.473, -0.393,
+                           0.292,  0.571, -0.491,  0.444, -0.288,  0.198, -0.343,  0.015,
+                           0.232,  0.088,  0.228,  0.151, -0.136,  0.236, -0.273, -0.259,
+                           -0.217,  0.359, -0.207,  0.352, -0.142,  0.192, -0.061, -0.17 ,
+                           -0.343,  0.189, -0.221,  0.32 , -0.301, -0.1  ,  0.005,  0.232,
+                           -0.344,  0.136,  0.252,  0.157, -0.13 , -0.244,  0.193, -0.034,
+                           -0.12 , -0.193, -0.102,  0.252, -0.185, -0.167, -0.575,  0.582,
+                           -0.426,  0.983,  0.212,  0.204,  0.03 , -0.276, -0.425, -0.158]
+            k: 3
+            num_candidates: 3
+
+  - match: { hits.total: 3 }
+  - set: { hits.hits.0._score: rescore_score0 }
+  - set: { hits.hits.1._score: rescore_score1 }
+  - set: { hits.hits.2._score: rescore_score2 }
+
+  - do:
+      headers:
+        Content-Type: application/json
+      search:
+        rest_total_hits_as_int: true
+        index: bbq_rescore_hnsw
+        body:
+          query:
+            script_score:
+              query: {match_all: {} }
+              script:
+                source: "double similarity = dotProduct(params.query_vector, 'vector'); return similarity < 0 ? 1 / (1 + -1 * similarity) : similarity + 1"
+                params:
+                  query_vector: [0.128,  0.067, -0.08 ,  0.395, -0.11 , -0.259,  0.473, -0.393,
+                                 0.292,  0.571, -0.491,  0.444, -0.288,  0.198, -0.343,  0.015,
+                                 0.232,  0.088,  0.228,  0.151, -0.136,  0.236, -0.273, -0.259,
+                                 -0.217,  0.359, -0.207,  0.352, -0.142,  0.192, -0.061, -0.17 ,
+                                 -0.343,  0.189, -0.221,  0.32 , -0.301, -0.1  ,  0.005,  0.232,
+                                 -0.344,  0.136,  0.252,  0.157, -0.13 , -0.244,  0.193, -0.034,
+                                 -0.12 , -0.193, -0.102,  0.252, -0.185, -0.167, -0.575,  0.582,
+                                 -0.426,  0.983,  0.212,  0.204,  0.03 , -0.276, -0.425, -0.158]
+
+  # Compare scores as hit IDs may change depending on how things are distributed
+  - match: { hits.total: 3 }
+  - match: { hits.hits.0._score: $rescore_score0 }
+  - match: { hits.hits.1._score: $rescore_score1 }
+  - match: { hits.hits.2._score: $rescore_score2 }

rest-api-spec/src/yamlRestTest/resources/rest-api-spec/test/search.vectors/41_knn_search_byte_quantized.yml

@@ -611,3 +611,92 @@ setup:
   - match: { hits.hits.0._id: "1"}
   - match: { hits.hits.1._id: "2"}
   - match: { hits.hits.2._id: "3"}
+---
+"Test index configured rescore vector":
+  - requires:
+      cluster_features: ["mapper.dense_vector.rescore_vector"]
+      reason: Needs rescore_vector feature
+  - skip:
+      features: "headers"
+  - do:
+      indices.create:
+        index: int8_rescore_hnsw
+        body:
+          settings:
+            index:
+              number_of_shards: 1
+          mappings:
+            properties:
+              vector:
+                type: dense_vector
+                dims: 64
+                index: true
+                similarity: max_inner_product
+                index_options:
+                  type: int8_hnsw
+                  rescore_vector:
+                    oversample: 1.5
+
+  - do:
+      bulk:
+        index: int8_rescore_hnsw
+        refresh: true
+        body: |
+          { "index": {"_id": "1"}}
+          { "vector": [0.077,  0.32 , -0.205,  0.63 ,  0.032,  0.201,  0.167, -0.313, 0.176,  0.531, -0.375,  0.334, -0.046,  0.078, -0.349,  0.272, 0.307, -0.083,  0.504,  0.255, -0.404,  0.289, -0.226, -0.132, -0.216,  0.49 ,  0.039,  0.507, -0.307,  0.107,  0.09 , -0.265, -0.285,  0.336, -0.272,  0.369, -0.282,  0.086, -0.132,  0.475, -0.224,  0.203,  0.439,  0.064,  0.246, -0.396,  0.297,  0.242, -0.028,  0.321, -0.022, -0.009, -0.001  ,  0.031, -0.533,  0.45, -0.683,  1.331,  0.194, -0.157, -0.1  , -0.279, -0.098, -0.176] }
+          { "index": {"_id": "2"}}
+          { "vector": [0.196,  0.514,  0.039,  0.555, -0.042,  0.242,  0.463, -0.348, -0.08 ,  0.442, -0.067, -0.05 , -0.001,  0.298, -0.377,  0.048, 0.307,  0.159,  0.278,  0.119, -0.057,  0.333, -0.289, -0.438, -0.014,  0.361, -0.169,  0.292, -0.229,  0.123,  0.031, -0.138, -0.139,  0.315, -0.216,  0.322, -0.445, -0.059,  0.071,  0.429, -0.602, -0.142,  0.11 ,  0.192,  0.259, -0.241,  0.181, -0.166, 0.082,  0.107, -0.05 ,  0.155,  0.011,  0.161, -0.486,  0.569, -0.489,  0.901,  0.208,  0.011, -0.209, -0.153, -0.27 , -0.013] }
+          { "index": {"_id": "3"}}
+          { "vector": [0.196,  0.514,  0.039,  0.555, -0.042,  0.242,  0.463, -0.348, -0.08 ,  0.442, -0.067, -0.05 , -0.001,  0.298, -0.377,  0.048, 0.307,  0.159,  0.278,  0.119, -0.057,  0.333, -0.289, -0.438, -0.014,  0.361, -0.169,  0.292, -0.229,  0.123,  0.031, -0.138, -0.139,  0.315, -0.216,  0.322, -0.445, -0.059,  0.071,  0.429, -0.602, -0.142,  0.11 ,  0.192,  0.259, -0.241,  0.181, -0.166, 0.082,  0.107, -0.05 ,  0.155,  0.011,  0.161, -0.486,  0.569, -0.489,  0.901,  0.208,  0.011, -0.209, -0.153, -0.27 , -0.013] }
+
+  - do:
+      headers:
+        Content-Type: application/json
+      search:
+        rest_total_hits_as_int: true
+        index: int8_rescore_hnsw
+        body:
+          knn:
+            field: vector
+            query_vector: [0.128,  0.067, -0.08 ,  0.395, -0.11 , -0.259,  0.473, -0.393,
+                           0.292,  0.571, -0.491,  0.444, -0.288,  0.198, -0.343,  0.015,
+                           0.232,  0.088,  0.228,  0.151, -0.136,  0.236, -0.273, -0.259,
+                           -0.217,  0.359, -0.207,  0.352, -0.142,  0.192, -0.061, -0.17 ,
+                           -0.343,  0.189, -0.221,  0.32 , -0.301, -0.1  ,  0.005,  0.232,
+                           -0.344,  0.136,  0.252,  0.157, -0.13 , -0.244,  0.193, -0.034,
+                           -0.12 , -0.193, -0.102,  0.252, -0.185, -0.167, -0.575,  0.582,
+                           -0.426,  0.983,  0.212,  0.204,  0.03 , -0.276, -0.425, -0.158]
+            k: 3
+            num_candidates: 3
+
+  - match: { hits.total: 3 }
+  - set: { hits.hits.0._score: rescore_score0 }
+  - set: { hits.hits.1._score: rescore_score1 }
+  - set: { hits.hits.2._score: rescore_score2 }
+
+  - do:
+      headers:
+        Content-Type: application/json
+      search:
+        rest_total_hits_as_int: true
+        body:
+          query:
+            script_score:
+              query: {match_all: {} }
+              script:
+                source: "double similarity = dotProduct(params.query_vector, 'vector'); return similarity < 0 ? 1 / (1 + -1 * similarity) : similarity + 1"
+                params:
+                  query_vector: [0.128,  0.067, -0.08 ,  0.395, -0.11 , -0.259,  0.473, -0.393,
+                                 0.292,  0.571, -0.491,  0.444, -0.288,  0.198, -0.343,  0.015,
+                                 0.232,  0.088,  0.228,  0.151, -0.136,  0.236, -0.273, -0.259,
+                                 -0.217,  0.359, -0.207,  0.352, -0.142,  0.192, -0.061, -0.17 ,
+                                 -0.343,  0.189, -0.221,  0.32 , -0.301, -0.1  ,  0.005,  0.232,
+                                 -0.344,  0.136,  0.252,  0.157, -0.13 , -0.244,  0.193, -0.034,
+                                 -0.12 , -0.193, -0.102,  0.252, -0.185, -0.167, -0.575,  0.582,
+                                 -0.426,  0.983,  0.212,  0.204,  0.03 , -0.276, -0.425, -0.158]
+
+  # Compare scores as hit IDs may change depending on how things are distributed
+  - match: { hits.total: 3 }
+  - match: { hits.hits.0._score: $rescore_score0 }
+  - match: { hits.hits.1._score: $rescore_score1 }
+  - match: { hits.hits.2._score: $rescore_score2 }

rest-api-spec/src/yamlRestTest/resources/rest-api-spec/test/search.vectors/41_knn_search_half_byte_quantized.yml

@@ -642,3 +642,92 @@ setup:
         index: dynamic_dim_hnsw_quantized
         body:
           vector: [1.0, 2.0, 3.0, 4.0, 5.0, 6.0]
+---
+"Test index configured rescore vector":
+  - requires:
+      cluster_features: ["mapper.dense_vector.rescore_vector"]
+      reason: Needs rescore_vector feature
+  - skip:
+      features: "headers"
+  - do:
+      indices.create:
+        index: int4_rescore_hnsw
+        body:
+          settings:
+            index:
+              number_of_shards: 1
+          mappings:
+            properties:
+              vector:
+                type: dense_vector
+                dims: 64
+                index: true
+                similarity: max_inner_product
+                index_options:
+                  type: int4_hnsw
+                  rescore_vector:
+                    oversample: 1.5
+
+  - do:
+      bulk:
+        index: int4_rescore_hnsw
+        refresh: true
+        body: |
+          { "index": {"_id": "1"}}
+          { "vector": [0.077,  0.32 , -0.205,  0.63 ,  0.032,  0.201,  0.167, -0.313, 0.176,  0.531, -0.375,  0.334, -0.046,  0.078, -0.349,  0.272, 0.307, -0.083,  0.504,  0.255, -0.404,  0.289, -0.226, -0.132, -0.216,  0.49 ,  0.039,  0.507, -0.307,  0.107,  0.09 , -0.265, -0.285,  0.336, -0.272,  0.369, -0.282,  0.086, -0.132,  0.475, -0.224,  0.203,  0.439,  0.064,  0.246, -0.396,  0.297,  0.242, -0.028,  0.321, -0.022, -0.009, -0.001  ,  0.031, -0.533,  0.45, -0.683,  1.331,  0.194, -0.157, -0.1  , -0.279, -0.098, -0.176] }
+          { "index": {"_id": "2"}}
+          { "vector": [0.196,  0.514,  0.039,  0.555, -0.042,  0.242,  0.463, -0.348, -0.08 ,  0.442, -0.067, -0.05 , -0.001,  0.298, -0.377,  0.048, 0.307,  0.159,  0.278,  0.119, -0.057,  0.333, -0.289, -0.438, -0.014,  0.361, -0.169,  0.292, -0.229,  0.123,  0.031, -0.138, -0.139,  0.315, -0.216,  0.322, -0.445, -0.059,  0.071,  0.429, -0.602, -0.142,  0.11 ,  0.192,  0.259, -0.241,  0.181, -0.166, 0.082,  0.107, -0.05 ,  0.155,  0.011,  0.161, -0.486,  0.569, -0.489,  0.901,  0.208,  0.011, -0.209, -0.153, -0.27 , -0.013] }
+          { "index": {"_id": "3"}}
+          { "vector": [0.196,  0.514,  0.039,  0.555, -0.042,  0.242,  0.463, -0.348, -0.08 ,  0.442, -0.067, -0.05 , -0.001,  0.298, -0.377,  0.048, 0.307,  0.159,  0.278,  0.119, -0.057,  0.333, -0.289, -0.438, -0.014,  0.361, -0.169,  0.292, -0.229,  0.123,  0.031, -0.138, -0.139,  0.315, -0.216,  0.322, -0.445, -0.059,  0.071,  0.429, -0.602, -0.142,  0.11 ,  0.192,  0.259, -0.241,  0.181, -0.166, 0.082,  0.107, -0.05 ,  0.155,  0.011,  0.161, -0.486,  0.569, -0.489,  0.901,  0.208,  0.011, -0.209, -0.153, -0.27 , -0.013] }
+
+  - do:
+      headers:
+        Content-Type: application/json
+      search:
+        rest_total_hits_as_int: true
+        index: int4_rescore_hnsw
+        body:
+          knn:
+            field: vector
+            query_vector: [0.128,  0.067, -0.08 ,  0.395, -0.11 , -0.259,  0.473, -0.393,
+                           0.292,  0.571, -0.491,  0.444, -0.288,  0.198, -0.343,  0.015,
+                           0.232,  0.088,  0.228,  0.151, -0.136,  0.236, -0.273, -0.259,
+                           -0.217,  0.359, -0.207,  0.352, -0.142,  0.192, -0.061, -0.17 ,
+                           -0.343,  0.189, -0.221,  0.32 , -0.301, -0.1  ,  0.005,  0.232,
+                           -0.344,  0.136,  0.252,  0.157, -0.13 , -0.244,  0.193, -0.034,
+                           -0.12 , -0.193, -0.102,  0.252, -0.185, -0.167, -0.575,  0.582,
+                           -0.426,  0.983,  0.212,  0.204,  0.03 , -0.276, -0.425, -0.158]
+            k: 3
+            num_candidates: 3
+
+  - match: { hits.total: 3 }
+  - set: { hits.hits.0._score: rescore_score0 }
+  - set: { hits.hits.1._score: rescore_score1 }
+  - set: { hits.hits.2._score: rescore_score2 }
+
+  - do:
+      headers:
+        Content-Type: application/json
+      search:
+        rest_total_hits_as_int: true
+        body:
+          query:
+            script_score:
+              query: {match_all: {} }
+              script:
+                source: "double similarity = dotProduct(params.query_vector, 'vector'); return similarity < 0 ? 1 / (1 + -1 * similarity) : similarity + 1"
+                params:
+                  query_vector: [0.128,  0.067, -0.08 ,  0.395, -0.11 , -0.259,  0.473, -0.393,
+                                 0.292,  0.571, -0.491,  0.444, -0.288,  0.198, -0.343,  0.015,
+                                 0.232,  0.088,  0.228,  0.151, -0.136,  0.236, -0.273, -0.259,
+                                 -0.217,  0.359, -0.207,  0.352, -0.142,  0.192, -0.061, -0.17 ,
+                                 -0.343,  0.189, -0.221,  0.32 , -0.301, -0.1  ,  0.005,  0.232,
+                                 -0.344,  0.136,  0.252,  0.157, -0.13 , -0.244,  0.193, -0.034,
+                                 -0.12 , -0.193, -0.102,  0.252, -0.185, -0.167, -0.575,  0.582,
+                                 -0.426,  0.983,  0.212,  0.204,  0.03 , -0.276, -0.425, -0.158]
+
+  # Compare scores as hit IDs may change depending on how things are distributed
+  - match: { hits.total: 3 }
+  - match: { hits.hits.0._score: $rescore_score0 }
+  - match: { hits.hits.1._score: $rescore_score1 }
+  - match: { hits.hits.2._score: $rescore_score2 }

rest-api-spec/src/yamlRestTest/resources/rest-api-spec/test/search.vectors/42_knn_search_bbq_flat.yml

@@ -249,3 +249,93 @@ setup:
         index: dynamic_dim_bbq_flat
         body:
           vector: [1.0, 2.0, 3.0, 4.0, 1.0, 2.0, 3.0, 4.0, 1.0, 2.0, 3.0, 4.0, 1.0, 2.0, 3.0, 4.0, 1.0, 2.0, 3.0, 4.0, 1.0, 2.0, 3.0, 4.0, 1.0, 2.0, 3.0, 4.0, 1.0, 2.0, 3.0, 4.0, 1.0, 2.0, 3.0, 4.0, 1.0, 2.0, 3.0, 4.0, 1.0, 2.0, 3.0, 4.0, 1.0, 2.0, 3.0, 4.0, 1.0, 2.0, 3.0, 4.0, 1.0, 2.0, 3.0, 4.0, 1.0, 2.0, 3.0, 4.0, 1.0, 2.0, 3.0, 4.0]
+---
+"Test index configured rescore vector":
+  - requires:
+      cluster_features: ["mapper.dense_vector.rescore_vector"]
+      reason: Needs rescore_vector feature
+  - skip:
+      features: "headers"
+  - do:
+      indices.create:
+        index: bbq_rescore_flat
+        body:
+          settings:
+            index:
+              number_of_shards: 1
+          mappings:
+            properties:
+              vector:
+                type: dense_vector
+                dims: 64
+                index: true
+                similarity: max_inner_product
+                index_options:
+                  type: bbq_flat
+                  rescore_vector:
+                    oversample: 1.5
+
+  - do:
+      bulk:
+        index: bbq_rescore_flat
+        refresh: true
+        body: |
+          { "index": {"_id": "1"}}
+          { "vector": [0.077,  0.32 , -0.205,  0.63 ,  0.032,  0.201,  0.167, -0.313, 0.176,  0.531, -0.375,  0.334, -0.046,  0.078, -0.349,  0.272, 0.307, -0.083,  0.504,  0.255, -0.404,  0.289, -0.226, -0.132, -0.216,  0.49 ,  0.039,  0.507, -0.307,  0.107,  0.09 , -0.265, -0.285,  0.336, -0.272,  0.369, -0.282,  0.086, -0.132,  0.475, -0.224,  0.203,  0.439,  0.064,  0.246, -0.396,  0.297,  0.242, -0.028,  0.321, -0.022, -0.009, -0.001  ,  0.031, -0.533,  0.45, -0.683,  1.331,  0.194, -0.157, -0.1  , -0.279, -0.098, -0.176] }
+          { "index": {"_id": "2"}}
+          { "vector": [0.196,  0.514,  0.039,  0.555, -0.042,  0.242,  0.463, -0.348, -0.08 ,  0.442, -0.067, -0.05 , -0.001,  0.298, -0.377,  0.048, 0.307,  0.159,  0.278,  0.119, -0.057,  0.333, -0.289, -0.438, -0.014,  0.361, -0.169,  0.292, -0.229,  0.123,  0.031, -0.138, -0.139,  0.315, -0.216,  0.322, -0.445, -0.059,  0.071,  0.429, -0.602, -0.142,  0.11 ,  0.192,  0.259, -0.241,  0.181, -0.166, 0.082,  0.107, -0.05 ,  0.155,  0.011,  0.161, -0.486,  0.569, -0.489,  0.901,  0.208,  0.011, -0.209, -0.153, -0.27 , -0.013] }
+          { "index": {"_id": "3"}}
+          { "vector": [0.196,  0.514,  0.039,  0.555, -0.042,  0.242,  0.463, -0.348, -0.08 ,  0.442, -0.067, -0.05 , -0.001,  0.298, -0.377,  0.048, 0.307,  0.159,  0.278,  0.119, -0.057,  0.333, -0.289, -0.438, -0.014,  0.361, -0.169,  0.292, -0.229,  0.123,  0.031, -0.138, -0.139,  0.315, -0.216,  0.322, -0.445, -0.059,  0.071,  0.429, -0.602, -0.142,  0.11 ,  0.192,  0.259, -0.241,  0.181, -0.166, 0.082,  0.107, -0.05 ,  0.155,  0.011,  0.161, -0.486,  0.569, -0.489,  0.901,  0.208,  0.011, -0.209, -0.153, -0.27 , -0.013] }
+
+  - do:
+      headers:
+        Content-Type: application/json
+      search:
+        rest_total_hits_as_int: true
+        index: bbq_rescore_flat
+        body:
+          knn:
+            field: vector
+            query_vector: [0.128,  0.067, -0.08 ,  0.395, -0.11 , -0.259,  0.473, -0.393,
+                           0.292,  0.571, -0.491,  0.444, -0.288,  0.198, -0.343,  0.015,
+                           0.232,  0.088,  0.228,  0.151, -0.136,  0.236, -0.273, -0.259,
+                           -0.217,  0.359, -0.207,  0.352, -0.142,  0.192, -0.061, -0.17 ,
+                           -0.343,  0.189, -0.221,  0.32 , -0.301, -0.1  ,  0.005,  0.232,
+                           -0.344,  0.136,  0.252,  0.157, -0.13 , -0.244,  0.193, -0.034,
+                           -0.12 , -0.193, -0.102,  0.252, -0.185, -0.167, -0.575,  0.582,
+                           -0.426,  0.983,  0.212,  0.204,  0.03 , -0.276, -0.425, -0.158]
+            k: 3
+            num_candidates: 3
+
+  - match: { hits.total: 3 }
+  - set: { hits.hits.0._score: rescore_score0 }
+  - set: { hits.hits.1._score: rescore_score1 }
+  - set: { hits.hits.2._score: rescore_score2 }
+
+  - do:
+      headers:
+        Content-Type: application/json
+      search:
+        rest_total_hits_as_int: true
+        index: bbq_rescore_flat
+        body:
+          query:
+            script_score:
+              query: {match_all: {} }
+              script:
+                source: "double similarity = dotProduct(params.query_vector, 'vector'); return similarity < 0 ? 1 / (1 + -1 * similarity) : similarity + 1"
+                params:
+                  query_vector: [0.128,  0.067, -0.08 ,  0.395, -0.11 , -0.259,  0.473, -0.393,
+                                 0.292,  0.571, -0.491,  0.444, -0.288,  0.198, -0.343,  0.015,
+                                 0.232,  0.088,  0.228,  0.151, -0.136,  0.236, -0.273, -0.259,
+                                 -0.217,  0.359, -0.207,  0.352, -0.142,  0.192, -0.061, -0.17 ,
+                                 -0.343,  0.189, -0.221,  0.32 , -0.301, -0.1  ,  0.005,  0.232,
+                                 -0.344,  0.136,  0.252,  0.157, -0.13 , -0.244,  0.193, -0.034,
+                                 -0.12 , -0.193, -0.102,  0.252, -0.185, -0.167, -0.575,  0.582,
+                                 -0.426,  0.983,  0.212,  0.204,  0.03 , -0.276, -0.425, -0.158]
+
+  # Compare scores as hit IDs may change depending on how things are distributed
+  - match: { hits.total: 3 }
+  - match: { hits.hits.0._score: $rescore_score0 }
+  - match: { hits.hits.1._score: $rescore_score1 }
+  - match: { hits.hits.2._score: $rescore_score2 }

rest-api-spec/src/yamlRestTest/resources/rest-api-spec/test/search.vectors/42_knn_search_int4_flat.yml

@@ -405,3 +405,93 @@ setup:
   - match: { hits.hits.0._score: $rescore_score0 }
   - match: { hits.hits.1._score: $rescore_score1 }
   - match: { hits.hits.2._score: $rescore_score2 }
+---
+"Test index configured rescore vector":
+  - requires:
+      cluster_features: ["mapper.dense_vector.rescore_vector"]
+      reason: Needs rescore_vector feature
+  - skip:
+      features: "headers"
+  - do:
+      indices.create:
+        index: int4_rescore_flat
+        body:
+          settings:
+            index:
+              number_of_shards: 1
+          mappings:
+            properties:
+              vector:
+                type: dense_vector
+                dims: 64
+                index: true
+                similarity: max_inner_product
+                index_options:
+                  type: int4_flat
+                  rescore_vector:
+                    oversample: 1.5
+
+  - do:
+      bulk:
+        index: int4_rescore_flat
+        refresh: true
+        body: |
+          { "index": {"_id": "1"}}
+          { "vector": [0.077,  0.32 , -0.205,  0.63 ,  0.032,  0.201,  0.167, -0.313, 0.176,  0.531, -0.375,  0.334, -0.046,  0.078, -0.349,  0.272, 0.307, -0.083,  0.504,  0.255, -0.404,  0.289, -0.226, -0.132, -0.216,  0.49 ,  0.039,  0.507, -0.307,  0.107,  0.09 , -0.265, -0.285,  0.336, -0.272,  0.369, -0.282,  0.086, -0.132,  0.475, -0.224,  0.203,  0.439,  0.064,  0.246, -0.396,  0.297,  0.242, -0.028,  0.321, -0.022, -0.009, -0.001  ,  0.031, -0.533,  0.45, -0.683,  1.331,  0.194, -0.157, -0.1  , -0.279, -0.098, -0.176] }
+          { "index": {"_id": "2"}}
+          { "vector": [0.196,  0.514,  0.039,  0.555, -0.042,  0.242,  0.463, -0.348, -0.08 ,  0.442, -0.067, -0.05 , -0.001,  0.298, -0.377,  0.048, 0.307,  0.159,  0.278,  0.119, -0.057,  0.333, -0.289, -0.438, -0.014,  0.361, -0.169,  0.292, -0.229,  0.123,  0.031, -0.138, -0.139,  0.315, -0.216,  0.322, -0.445, -0.059,  0.071,  0.429, -0.602, -0.142,  0.11 ,  0.192,  0.259, -0.241,  0.181, -0.166, 0.082,  0.107, -0.05 ,  0.155,  0.011,  0.161, -0.486,  0.569, -0.489,  0.901,  0.208,  0.011, -0.209, -0.153, -0.27 , -0.013] }
+          { "index": {"_id": "3"}}
+          { "vector": [0.196,  0.514,  0.039,  0.555, -0.042,  0.242,  0.463, -0.348, -0.08 ,  0.442, -0.067, -0.05 , -0.001,  0.298, -0.377,  0.048, 0.307,  0.159,  0.278,  0.119, -0.057,  0.333, -0.289, -0.438, -0.014,  0.361, -0.169,  0.292, -0.229,  0.123,  0.031, -0.138, -0.139,  0.315, -0.216,  0.322, -0.445, -0.059,  0.071,  0.429, -0.602, -0.142,  0.11 ,  0.192,  0.259, -0.241,  0.181, -0.166, 0.082,  0.107, -0.05 ,  0.155,  0.011,  0.161, -0.486,  0.569, -0.489,  0.901,  0.208,  0.011, -0.209, -0.153, -0.27 , -0.013] }
+
+  - do:
+      headers:
+        Content-Type: application/json
+      search:
+        rest_total_hits_as_int: true
+        index: int4_rescore_flat
+        body:
+          knn:
+            field: vector
+            query_vector: [0.128,  0.067, -0.08 ,  0.395, -0.11 , -0.259,  0.473, -0.393,
+                           0.292,  0.571, -0.491,  0.444, -0.288,  0.198, -0.343,  0.015,
+                           0.232,  0.088,  0.228,  0.151, -0.136,  0.236, -0.273, -0.259,
+                           -0.217,  0.359, -0.207,  0.352, -0.142,  0.192, -0.061, -0.17 ,
+                           -0.343,  0.189, -0.221,  0.32 , -0.301, -0.1  ,  0.005,  0.232,
+                           -0.344,  0.136,  0.252,  0.157, -0.13 , -0.244,  0.193, -0.034,
+                           -0.12 , -0.193, -0.102,  0.252, -0.185, -0.167, -0.575,  0.582,
+                           -0.426,  0.983,  0.212,  0.204,  0.03 , -0.276, -0.425, -0.158]
+            k: 3
+            num_candidates: 3
+
+  - match: { hits.total: 3 }
+  - set: { hits.hits.0._score: rescore_score0 }
+  - set: { hits.hits.1._score: rescore_score1 }
+  - set: { hits.hits.2._score: rescore_score2 }
+
+  - do:
+      headers:
+        Content-Type: application/json
+      search:
+        rest_total_hits_as_int: true
+        index: int4_rescore_flat
+        body:
+          query:
+            script_score:
+              query: {match_all: {} }
+              script:
+                source: "double similarity = dotProduct(params.query_vector, 'vector'); return similarity < 0 ? 1 / (1 + -1 * similarity) : similarity + 1"
+                params:
+                  query_vector: [0.128,  0.067, -0.08 ,  0.395, -0.11 , -0.259,  0.473, -0.393,
+                                 0.292,  0.571, -0.491,  0.444, -0.288,  0.198, -0.343,  0.015,
+                                 0.232,  0.088,  0.228,  0.151, -0.136,  0.236, -0.273, -0.259,
+                                 -0.217,  0.359, -0.207,  0.352, -0.142,  0.192, -0.061, -0.17 ,
+                                 -0.343,  0.189, -0.221,  0.32 , -0.301, -0.1  ,  0.005,  0.232,
+                                 -0.344,  0.136,  0.252,  0.157, -0.13 , -0.244,  0.193, -0.034,
+                                 -0.12 , -0.193, -0.102,  0.252, -0.185, -0.167, -0.575,  0.582,
+                                 -0.426,  0.983,  0.212,  0.204,  0.03 , -0.276, -0.425, -0.158]
+
+  # Compare scores as hit IDs may change depending on how things are distributed
+  - match: { hits.total: 3 }
+  - match: { hits.hits.0._score: $rescore_score0 }
+  - match: { hits.hits.1._score: $rescore_score1 }
+  - match: { hits.hits.2._score: $rescore_score2 }

rest-api-spec/src/yamlRestTest/resources/rest-api-spec/test/search.vectors/42_knn_search_int8_flat.yml

@@ -346,3 +346,93 @@ setup:
                 index: true
                 index_options:
                   type: int8_flat
+---
+"Test index configured rescore vector":
+  - requires:
+      cluster_features: ["mapper.dense_vector.rescore_vector"]
+      reason: Needs rescore_vector feature
+  - skip:
+      features: "headers"
+  - do:
+      indices.create:
+        index: int8_rescore_flat
+        body:
+          settings:
+            index:
+              number_of_shards: 1
+          mappings:
+            properties:
+              vector:
+                type: dense_vector
+                dims: 64
+                index: true
+                similarity: max_inner_product
+                index_options:
+                  type: int8_flat
+                  rescore_vector:
+                    oversample: 1.5
+
+  - do:
+      bulk:
+        index: int8_rescore_flat
+        refresh: true
+        body: |
+          { "index": {"_id": "1"}}
+          { "vector": [0.077,  0.32 , -0.205,  0.63 ,  0.032,  0.201,  0.167, -0.313, 0.176,  0.531, -0.375,  0.334, -0.046,  0.078, -0.349,  0.272, 0.307, -0.083,  0.504,  0.255, -0.404,  0.289, -0.226, -0.132, -0.216,  0.49 ,  0.039,  0.507, -0.307,  0.107,  0.09 , -0.265, -0.285,  0.336, -0.272,  0.369, -0.282,  0.086, -0.132,  0.475, -0.224,  0.203,  0.439,  0.064,  0.246, -0.396,  0.297,  0.242, -0.028,  0.321, -0.022, -0.009, -0.001  ,  0.031, -0.533,  0.45, -0.683,  1.331,  0.194, -0.157, -0.1  , -0.279, -0.098, -0.176] }
+          { "index": {"_id": "2"}}
+          { "vector": [0.196,  0.514,  0.039,  0.555, -0.042,  0.242,  0.463, -0.348, -0.08 ,  0.442, -0.067, -0.05 , -0.001,  0.298, -0.377,  0.048, 0.307,  0.159,  0.278,  0.119, -0.057,  0.333, -0.289, -0.438, -0.014,  0.361, -0.169,  0.292, -0.229,  0.123,  0.031, -0.138, -0.139,  0.315, -0.216,  0.322, -0.445, -0.059,  0.071,  0.429, -0.602, -0.142,  0.11 ,  0.192,  0.259, -0.241,  0.181, -0.166, 0.082,  0.107, -0.05 ,  0.155,  0.011,  0.161, -0.486,  0.569, -0.489,  0.901,  0.208,  0.011, -0.209, -0.153, -0.27 , -0.013] }
+          { "index": {"_id": "3"}}
+          { "vector": [0.196,  0.514,  0.039,  0.555, -0.042,  0.242,  0.463, -0.348, -0.08 ,  0.442, -0.067, -0.05 , -0.001,  0.298, -0.377,  0.048, 0.307,  0.159,  0.278,  0.119, -0.057,  0.333, -0.289, -0.438, -0.014,  0.361, -0.169,  0.292, -0.229,  0.123,  0.031, -0.138, -0.139,  0.315, -0.216,  0.322, -0.445, -0.059,  0.071,  0.429, -0.602, -0.142,  0.11 ,  0.192,  0.259, -0.241,  0.181, -0.166, 0.082,  0.107, -0.05 ,  0.155,  0.011,  0.161, -0.486,  0.569, -0.489,  0.901,  0.208,  0.011, -0.209, -0.153, -0.27 , -0.013] }
+
+  - do:
+      headers:
+        Content-Type: application/json
+      search:
+        rest_total_hits_as_int: true
+        index: int8_rescore_flat
+        body:
+          knn:
+            field: vector
+            query_vector: [0.128,  0.067, -0.08 ,  0.395, -0.11 , -0.259,  0.473, -0.393,
+                           0.292,  0.571, -0.491,  0.444, -0.288,  0.198, -0.343,  0.015,
+                           0.232,  0.088,  0.228,  0.151, -0.136,  0.236, -0.273, -0.259,
+                           -0.217,  0.359, -0.207,  0.352, -0.142,  0.192, -0.061, -0.17 ,
+                           -0.343,  0.189, -0.221,  0.32 , -0.301, -0.1  ,  0.005,  0.232,
+                           -0.344,  0.136,  0.252,  0.157, -0.13 , -0.244,  0.193, -0.034,
+                           -0.12 , -0.193, -0.102,  0.252, -0.185, -0.167, -0.575,  0.582,
+                           -0.426,  0.983,  0.212,  0.204,  0.03 , -0.276, -0.425, -0.158]
+            k: 3
+            num_candidates: 3
+
+  - match: { hits.total: 3 }
+  - set: { hits.hits.0._score: rescore_score0 }
+  - set: { hits.hits.1._score: rescore_score1 }
+  - set: { hits.hits.2._score: rescore_score2 }
+
+  - do:
+      headers:
+        Content-Type: application/json
+      search:
+        rest_total_hits_as_int: true
+        index: int8_rescore_flat
+        body:
+          query:
+            script_score:
+              query: {match_all: {} }
+              script:
+                source: "double similarity = dotProduct(params.query_vector, 'vector'); return similarity < 0 ? 1 / (1 + -1 * similarity) : similarity + 1"
+                params:
+                  query_vector: [0.128,  0.067, -0.08 ,  0.395, -0.11 , -0.259,  0.473, -0.393,
+                                 0.292,  0.571, -0.491,  0.444, -0.288,  0.198, -0.343,  0.015,
+                                 0.232,  0.088,  0.228,  0.151, -0.136,  0.236, -0.273, -0.259,
+                                 -0.217,  0.359, -0.207,  0.352, -0.142,  0.192, -0.061, -0.17 ,
+                                 -0.343,  0.189, -0.221,  0.32 , -0.301, -0.1  ,  0.005,  0.232,
+                                 -0.344,  0.136,  0.252,  0.157, -0.13 , -0.244,  0.193, -0.034,
+                                 -0.12 , -0.193, -0.102,  0.252, -0.185, -0.167, -0.575,  0.582,
+                                 -0.426,  0.983,  0.212,  0.204,  0.03 , -0.276, -0.425, -0.158]
+
+  # Compare scores as hit IDs may change depending on how things are distributed
+  - match: { hits.total: 3 }
+  - match: { hits.hits.0._score: $rescore_score0 }
+  - match: { hits.hits.1._score: $rescore_score1 }
+  - match: { hits.hits.2._score: $rescore_score2 }

server/src/main/java/org/elasticsearch/index/IndexVersions.java

@@ -151,6 +151,7 @@ public class IndexVersions {
     public static final IndexVersion TIME_SERIES_ID_DOC_VALUES_SPARSE_INDEX = def(9_012_0_00, Version.LUCENE_10_1_0);
     public static final IndexVersion SYNTHETIC_SOURCE_STORE_ARRAYS_NATIVELY_KEYWORD = def(9_013_0_00, Version.LUCENE_10_1_0);
     public static final IndexVersion SYNTHETIC_SOURCE_STORE_ARRAYS_NATIVELY_IP = def(9_014_0_00, Version.LUCENE_10_1_0);
+    public static final IndexVersion ADD_RESCORE_PARAMS_TO_QUANTIZED_VECTORS = def(9_015_0_00, Version.LUCENE_10_1_0);
     /*
      * STOP! READ THIS FIRST! No, really,
      *        ____ _____ ___  ____  _        ____  _____    _    ____    _____ _   _ ___ ____    _____ ___ ____  ____ _____ _

server/src/main/java/org/elasticsearch/index/mapper/MapperFeatures.java

@@ -14,6 +14,8 @@ import org.elasticsearch.features.NodeFeature;
 
 import java.util.Set;
 
+import static org.elasticsearch.index.mapper.vectors.DenseVectorFieldMapper.RESCORE_VECTOR_QUANTIZED_VECTOR_MAPPING;
+
 /**
  * Spec for mapper-related features.
  */
@@ -58,7 +60,8 @@ public class MapperFeatures implements FeatureSpecification {
             SourceFieldMapper.SYNTHETIC_RECOVERY_SOURCE,
             ObjectMapper.SUBOBJECTS_FALSE_MAPPING_UPDATE_FIX,
             UKNOWN_FIELD_MAPPING_UPDATE_ERROR_MESSAGE,
-            DOC_VALUES_SKIPPER
+            DOC_VALUES_SKIPPER,
+            RESCORE_VECTOR_QUANTIZED_VECTOR_MAPPING
         );
     }
 }

server/src/main/java/org/elasticsearch/index/mapper/vectors/DenseVectorFieldMapper.java

@@ -38,6 +38,7 @@ import org.apache.lucene.util.BytesRef;
 import org.apache.lucene.util.VectorUtil;
 import org.elasticsearch.common.ParsingException;
 import org.elasticsearch.common.xcontent.support.XContentMapValues;
+import org.elasticsearch.features.NodeFeature;
 import org.elasticsearch.index.IndexVersion;
 import org.elasticsearch.index.IndexVersions;
 import org.elasticsearch.index.codec.vectors.ES813FlatVectorFormat;
@@ -73,6 +74,7 @@ import org.elasticsearch.search.vectors.RescoreKnnVectorQuery;
 import org.elasticsearch.search.vectors.VectorData;
 import org.elasticsearch.search.vectors.VectorSimilarityQuery;
 import org.elasticsearch.xcontent.ToXContent;
+import org.elasticsearch.xcontent.ToXContentObject;
 import org.elasticsearch.xcontent.XContentBuilder;
 import org.elasticsearch.xcontent.XContentParser;
 import org.elasticsearch.xcontent.XContentParser.Token;
@@ -112,6 +114,9 @@ public class DenseVectorFieldMapper extends FieldMapper {
     public static final IndexVersion NORMALIZE_COSINE = IndexVersions.NORMALIZED_VECTOR_COSINE;
     public static final IndexVersion DEFAULT_TO_INT8 = DEFAULT_DENSE_VECTOR_TO_INT8_HNSW;
     public static final IndexVersion LITTLE_ENDIAN_FLOAT_STORED_INDEX_VERSION = IndexVersions.V_8_9_0;
+    public static final IndexVersion ADD_RESCORE_PARAMS_TO_QUANTIZED_VECTORS = IndexVersions.ADD_RESCORE_PARAMS_TO_QUANTIZED_VECTORS;
+
+    public static final NodeFeature RESCORE_VECTOR_QUANTIZED_VECTOR_MAPPING = new NodeFeature("mapper.dense_vector.rescore_vector");
 
     public static final String CONTENT_TYPE = "dense_vector";
     public static final short MAX_DIMS_COUNT = 4096; // maximum allowed number of dimensions
@@ -210,10 +215,11 @@ public class DenseVectorFieldMapper extends FieldMapper {
                     ? new Int8HnswIndexOptions(
                         Lucene99HnswVectorsFormat.DEFAULT_MAX_CONN,
                         Lucene99HnswVectorsFormat.DEFAULT_BEAM_WIDTH,
+                        null,
                         null
                     )
                     : null,
-                (n, c, o) -> o == null ? null : parseIndexOptions(n, o),
+                (n, c, o) -> o == null ? null : parseIndexOptions(n, o, indexVersionCreated),
                 m -> toType(m).indexOptions,
                 (b, n, v) -> {
                     if (v != null) {
@@ -1258,10 +1264,19 @@ public class DenseVectorFieldMapper extends FieldMapper {
         }
     }
 
+    abstract static class QuantizedIndexOptions extends IndexOptions {
+        final RescoreVector rescoreVector;
+
+        QuantizedIndexOptions(VectorIndexType type, RescoreVector rescoreVector) {
+            super(type);
+            this.rescoreVector = rescoreVector;
+        }
+    }
+
     public enum VectorIndexType {
         HNSW("hnsw", false) {
             @Override
-            public IndexOptions parseIndexOptions(String fieldName, Map<String, ?> indexOptionsMap) {
+            public IndexOptions parseIndexOptions(String fieldName, Map<String, ?> indexOptionsMap, IndexVersion indexVersion) {
                 Object mNode = indexOptionsMap.remove("m");
                 Object efConstructionNode = indexOptionsMap.remove("ef_construction");
                 if (mNode == null) {
@@ -1288,7 +1303,7 @@ public class DenseVectorFieldMapper extends FieldMapper {
         },
         INT8_HNSW("int8_hnsw", true) {
             @Override
-            public IndexOptions parseIndexOptions(String fieldName, Map<String, ?> indexOptionsMap) {
+            public IndexOptions parseIndexOptions(String fieldName, Map<String, ?> indexOptionsMap, IndexVersion indexVersion) {
                 Object mNode = indexOptionsMap.remove("m");
                 Object efConstructionNode = indexOptionsMap.remove("ef_construction");
                 Object confidenceIntervalNode = indexOptionsMap.remove("confidence_interval");
@@ -1304,8 +1319,12 @@ public class DenseVectorFieldMapper extends FieldMapper {
                 if (confidenceIntervalNode != null) {
                     confidenceInterval = (float) XContentMapValues.nodeDoubleValue(confidenceIntervalNode);
                 }
+                RescoreVector rescoreVector = null;
+                if (indexVersion.onOrAfter(ADD_RESCORE_PARAMS_TO_QUANTIZED_VECTORS)) {
+                    rescoreVector = RescoreVector.fromIndexOptions(indexOptionsMap);
+                }
                 MappingParser.checkNoRemainingFields(fieldName, indexOptionsMap);
-                return new Int8HnswIndexOptions(m, efConstruction, confidenceInterval);
+                return new Int8HnswIndexOptions(m, efConstruction, confidenceInterval, rescoreVector);
             }
 
             @Override
@@ -1319,7 +1338,7 @@ public class DenseVectorFieldMapper extends FieldMapper {
             }
         },
         INT4_HNSW("int4_hnsw", true) {
-            public IndexOptions parseIndexOptions(String fieldName, Map<String, ?> indexOptionsMap) {
+            public IndexOptions parseIndexOptions(String fieldName, Map<String, ?> indexOptionsMap, IndexVersion indexVersion) {
                 Object mNode = indexOptionsMap.remove("m");
                 Object efConstructionNode = indexOptionsMap.remove("ef_construction");
                 Object confidenceIntervalNode = indexOptionsMap.remove("confidence_interval");
@@ -1335,8 +1354,12 @@ public class DenseVectorFieldMapper extends FieldMapper {
                 if (confidenceIntervalNode != null) {
                     confidenceInterval = (float) XContentMapValues.nodeDoubleValue(confidenceIntervalNode);
                 }
+                RescoreVector rescoreVector = null;
+                if (indexVersion.onOrAfter(ADD_RESCORE_PARAMS_TO_QUANTIZED_VECTORS)) {
+                    rescoreVector = RescoreVector.fromIndexOptions(indexOptionsMap);
+                }
                 MappingParser.checkNoRemainingFields(fieldName, indexOptionsMap);
-                return new Int4HnswIndexOptions(m, efConstruction, confidenceInterval);
+                return new Int4HnswIndexOptions(m, efConstruction, confidenceInterval, rescoreVector);
             }
 
             @Override
@@ -1351,7 +1374,7 @@ public class DenseVectorFieldMapper extends FieldMapper {
         },
         FLAT("flat", false) {
             @Override
-            public IndexOptions parseIndexOptions(String fieldName, Map<String, ?> indexOptionsMap) {
+            public IndexOptions parseIndexOptions(String fieldName, Map<String, ?> indexOptionsMap, IndexVersion indexVersion) {
                 MappingParser.checkNoRemainingFields(fieldName, indexOptionsMap);
                 return new FlatIndexOptions();
             }
@@ -1368,14 +1391,18 @@ public class DenseVectorFieldMapper extends FieldMapper {
         },
         INT8_FLAT("int8_flat", true) {
             @Override
-            public IndexOptions parseIndexOptions(String fieldName, Map<String, ?> indexOptionsMap) {
+            public IndexOptions parseIndexOptions(String fieldName, Map<String, ?> indexOptionsMap, IndexVersion indexVersion) {
                 Object confidenceIntervalNode = indexOptionsMap.remove("confidence_interval");
                 Float confidenceInterval = null;
                 if (confidenceIntervalNode != null) {
                     confidenceInterval = (float) XContentMapValues.nodeDoubleValue(confidenceIntervalNode);
                 }
+                RescoreVector rescoreVector = null;
+                if (indexVersion.onOrAfter(ADD_RESCORE_PARAMS_TO_QUANTIZED_VECTORS)) {
+                    rescoreVector = RescoreVector.fromIndexOptions(indexOptionsMap);
+                }
                 MappingParser.checkNoRemainingFields(fieldName, indexOptionsMap);
-                return new Int8FlatIndexOptions(confidenceInterval);
+                return new Int8FlatIndexOptions(confidenceInterval, rescoreVector);
             }
 
             @Override
@@ -1390,14 +1417,18 @@ public class DenseVectorFieldMapper extends FieldMapper {
         },
         INT4_FLAT("int4_flat", true) {
             @Override
-            public IndexOptions parseIndexOptions(String fieldName, Map<String, ?> indexOptionsMap) {
+            public IndexOptions parseIndexOptions(String fieldName, Map<String, ?> indexOptionsMap, IndexVersion indexVersion) {
                 Object confidenceIntervalNode = indexOptionsMap.remove("confidence_interval");
                 Float confidenceInterval = null;
                 if (confidenceIntervalNode != null) {
                     confidenceInterval = (float) XContentMapValues.nodeDoubleValue(confidenceIntervalNode);
                 }
+                RescoreVector rescoreVector = null;
+                if (indexVersion.onOrAfter(ADD_RESCORE_PARAMS_TO_QUANTIZED_VECTORS)) {
+                    rescoreVector = RescoreVector.fromIndexOptions(indexOptionsMap);
+                }
                 MappingParser.checkNoRemainingFields(fieldName, indexOptionsMap);
-                return new Int4FlatIndexOptions(confidenceInterval);
+                return new Int4FlatIndexOptions(confidenceInterval, rescoreVector);
             }
 
             @Override
@@ -1412,7 +1443,7 @@ public class DenseVectorFieldMapper extends FieldMapper {
         },
         BBQ_HNSW("bbq_hnsw", true) {
             @Override
-            public IndexOptions parseIndexOptions(String fieldName, Map<String, ?> indexOptionsMap) {
+            public IndexOptions parseIndexOptions(String fieldName, Map<String, ?> indexOptionsMap, IndexVersion indexVersion) {
                 Object mNode = indexOptionsMap.remove("m");
                 Object efConstructionNode = indexOptionsMap.remove("ef_construction");
                 if (mNode == null) {
@@ -1423,8 +1454,12 @@ public class DenseVectorFieldMapper extends FieldMapper {
                 }
                 int m = XContentMapValues.nodeIntegerValue(mNode);
                 int efConstruction = XContentMapValues.nodeIntegerValue(efConstructionNode);
+                RescoreVector rescoreVector = null;
+                if (indexVersion.onOrAfter(ADD_RESCORE_PARAMS_TO_QUANTIZED_VECTORS)) {
+                    rescoreVector = RescoreVector.fromIndexOptions(indexOptionsMap);
+                }
                 MappingParser.checkNoRemainingFields(fieldName, indexOptionsMap);
-                return new BBQHnswIndexOptions(m, efConstruction);
+                return new BBQHnswIndexOptions(m, efConstruction, rescoreVector);
             }
 
             @Override
@@ -1439,9 +1474,13 @@ public class DenseVectorFieldMapper extends FieldMapper {
         },
         BBQ_FLAT("bbq_flat", true) {
             @Override
-            public IndexOptions parseIndexOptions(String fieldName, Map<String, ?> indexOptionsMap) {
+            public IndexOptions parseIndexOptions(String fieldName, Map<String, ?> indexOptionsMap, IndexVersion indexVersion) {
+                RescoreVector rescoreVector = null;
+                if (indexVersion.onOrAfter(ADD_RESCORE_PARAMS_TO_QUANTIZED_VECTORS)) {
+                    rescoreVector = RescoreVector.fromIndexOptions(indexOptionsMap);
+                }
                 MappingParser.checkNoRemainingFields(fieldName, indexOptionsMap);
-                return new BBQFlatIndexOptions();
+                return new BBQFlatIndexOptions(rescoreVector);
             }
 
             @Override
@@ -1467,7 +1506,7 @@ public class DenseVectorFieldMapper extends FieldMapper {
             this.quantized = quantized;
         }
 
-        abstract IndexOptions parseIndexOptions(String fieldName, Map<String, ?> indexOptionsMap);
+        abstract IndexOptions parseIndexOptions(String fieldName, Map<String, ?> indexOptionsMap, IndexVersion indexVersion);
 
         public abstract boolean supportsElementType(ElementType elementType);
 
@@ -1483,11 +1522,11 @@ public class DenseVectorFieldMapper extends FieldMapper {
         }
     }
 
-    static class Int8FlatIndexOptions extends IndexOptions {
+    static class Int8FlatIndexOptions extends QuantizedIndexOptions {
         private final Float confidenceInterval;
 
-        Int8FlatIndexOptions(Float confidenceInterval) {
-            super(VectorIndexType.INT8_FLAT);
+        Int8FlatIndexOptions(Float confidenceInterval, RescoreVector rescoreVector) {
+            super(VectorIndexType.INT8_FLAT, rescoreVector);
             this.confidenceInterval = confidenceInterval;
         }
 
@@ -1498,6 +1537,9 @@ public class DenseVectorFieldMapper extends FieldMapper {
             if (confidenceInterval != null) {
                 builder.field("confidence_interval", confidenceInterval);
             }
+            if (rescoreVector != null) {
+                rescoreVector.toXContent(builder, params);
+            }
             builder.endObject();
             return builder;
         }
@@ -1511,12 +1553,12 @@ public class DenseVectorFieldMapper extends FieldMapper {
         @Override
         boolean doEquals(IndexOptions o) {
             Int8FlatIndexOptions that = (Int8FlatIndexOptions) o;
-            return Objects.equals(confidenceInterval, that.confidenceInterval);
+            return Objects.equals(confidenceInterval, that.confidenceInterval) && Objects.equals(rescoreVector, that.rescoreVector);
         }
 
         @Override
         int doHashCode() {
-            return Objects.hash(confidenceInterval);
+            return Objects.hash(confidenceInterval, rescoreVector);
         }
 
         @Override
@@ -1567,13 +1609,13 @@ public class DenseVectorFieldMapper extends FieldMapper {
         }
     }
 
-    static class Int4HnswIndexOptions extends IndexOptions {
+    static class Int4HnswIndexOptions extends QuantizedIndexOptions {
         private final int m;
         private final int efConstruction;
         private final float confidenceInterval;
 
-        Int4HnswIndexOptions(int m, int efConstruction, Float confidenceInterval) {
-            super(VectorIndexType.INT4_HNSW);
+        Int4HnswIndexOptions(int m, int efConstruction, Float confidenceInterval, RescoreVector rescoreVector) {
+            super(VectorIndexType.INT4_HNSW, rescoreVector);
             this.m = m;
             this.efConstruction = efConstruction;
             // The default confidence interval for int4 is dynamic quantiles, this provides the best relevancy and is
@@ -1594,6 +1636,9 @@ public class DenseVectorFieldMapper extends FieldMapper {
             builder.field("m", m);
             builder.field("ef_construction", efConstruction);
             builder.field("confidence_interval", confidenceInterval);
+            if (rescoreVector != null) {
+                rescoreVector.toXContent(builder, params);
+            }
             builder.endObject();
             return builder;
         }
@@ -1601,12 +1646,15 @@ public class DenseVectorFieldMapper extends FieldMapper {
         @Override
         public boolean doEquals(IndexOptions o) {
             Int4HnswIndexOptions that = (Int4HnswIndexOptions) o;
-            return m == that.m && efConstruction == that.efConstruction && Objects.equals(confidenceInterval, that.confidenceInterval);
+            return m == that.m
+                && efConstruction == that.efConstruction
+                && Objects.equals(confidenceInterval, that.confidenceInterval)
+                && Objects.equals(rescoreVector, that.rescoreVector);
         }
 
         @Override
         public int doHashCode() {
-            return Objects.hash(m, efConstruction, confidenceInterval);
+            return Objects.hash(m, efConstruction, confidenceInterval, rescoreVector);
         }
 
         @Override
@@ -1619,6 +1667,8 @@ public class DenseVectorFieldMapper extends FieldMapper {
                 + efConstruction
                 + ", confidence_interval="
                 + confidenceInterval
+                + ", rescore_vector="
+                + (rescoreVector == null ? "none" : rescoreVector)
                 + "}";
         }
 
@@ -1635,11 +1685,11 @@ public class DenseVectorFieldMapper extends FieldMapper {
         }
     }
 
-    static class Int4FlatIndexOptions extends IndexOptions {
+    static class Int4FlatIndexOptions extends QuantizedIndexOptions {
         private final float confidenceInterval;
 
-        Int4FlatIndexOptions(Float confidenceInterval) {
-            super(VectorIndexType.INT4_FLAT);
+        Int4FlatIndexOptions(Float confidenceInterval, RescoreVector rescoreVector) {
+            super(VectorIndexType.INT4_FLAT, rescoreVector);
             // The default confidence interval for int4 is dynamic quantiles, this provides the best relevancy and is
             // effectively required for int4 to behave well across a wide range of data.
             this.confidenceInterval = confidenceInterval == null ? 0f : confidenceInterval;
@@ -1656,6 +1706,9 @@ public class DenseVectorFieldMapper extends FieldMapper {
             builder.startObject();
             builder.field("type", type);
             builder.field("confidence_interval", confidenceInterval);
+            if (rescoreVector != null) {
+                rescoreVector.toXContent(builder, params);
+            }
             builder.endObject();
             return builder;
         }
@@ -1665,17 +1718,17 @@ public class DenseVectorFieldMapper extends FieldMapper {
             if (this == o) return true;
             if (o == null || getClass() != o.getClass()) return false;
             Int4FlatIndexOptions that = (Int4FlatIndexOptions) o;
-            return Objects.equals(confidenceInterval, that.confidenceInterval);
+            return Objects.equals(confidenceInterval, that.confidenceInterval) && Objects.equals(rescoreVector, that.rescoreVector);
         }
 
         @Override
         public int doHashCode() {
-            return Objects.hash(confidenceInterval);
+            return Objects.hash(confidenceInterval, rescoreVector);
         }
 
         @Override
         public String toString() {
-            return "{type=" + type + ", confidence_interval=" + confidenceInterval + "}";
+            return "{type=" + type + ", confidence_interval=" + confidenceInterval + ", rescore_vector=" + rescoreVector + "}";
         }
 
         @Override
@@ -1689,13 +1742,13 @@ public class DenseVectorFieldMapper extends FieldMapper {
 
     }
 
-    static class Int8HnswIndexOptions extends IndexOptions {
+    static class Int8HnswIndexOptions extends QuantizedIndexOptions {
         private final int m;
         private final int efConstruction;
         private final Float confidenceInterval;
 
-        Int8HnswIndexOptions(int m, int efConstruction, Float confidenceInterval) {
-            super(VectorIndexType.INT8_HNSW);
+        Int8HnswIndexOptions(int m, int efConstruction, Float confidenceInterval, RescoreVector rescoreVector) {
+            super(VectorIndexType.INT8_HNSW, rescoreVector);
             this.m = m;
             this.efConstruction = efConstruction;
             this.confidenceInterval = confidenceInterval;
@@ -1716,6 +1769,9 @@ public class DenseVectorFieldMapper extends FieldMapper {
             if (confidenceInterval != null) {
                 builder.field("confidence_interval", confidenceInterval);
             }
+            if (rescoreVector != null) {
+                rescoreVector.toXContent(builder, params);
+            }
             builder.endObject();
             return builder;
         }
@@ -1725,12 +1781,15 @@ public class DenseVectorFieldMapper extends FieldMapper {
             if (this == o) return true;
             if (o == null || getClass() != o.getClass()) return false;
             Int8HnswIndexOptions that = (Int8HnswIndexOptions) o;
-            return m == that.m && efConstruction == that.efConstruction && Objects.equals(confidenceInterval, that.confidenceInterval);
+            return m == that.m
+                && efConstruction == that.efConstruction
+                && Objects.equals(confidenceInterval, that.confidenceInterval)
+                && Objects.equals(rescoreVector, that.rescoreVector);
         }
 
         @Override
         public int doHashCode() {
-            return Objects.hash(m, efConstruction, confidenceInterval);
+            return Objects.hash(m, efConstruction, confidenceInterval, rescoreVector);
         }
 
         @Override
@@ -1743,6 +1802,8 @@ public class DenseVectorFieldMapper extends FieldMapper {
                 + efConstruction
                 + ", confidence_interval="
                 + confidenceInterval
+                + ", rescore_vector="
+                + (rescoreVector == null ? "none" : rescoreVector)
                 + "}";
         }
 
@@ -1824,12 +1885,12 @@ public class DenseVectorFieldMapper extends FieldMapper {
         }
     }
 
-    static class BBQHnswIndexOptions extends IndexOptions {
+    static class BBQHnswIndexOptions extends QuantizedIndexOptions {
         private final int m;
         private final int efConstruction;
 
-        BBQHnswIndexOptions(int m, int efConstruction) {
-            super(VectorIndexType.BBQ_HNSW);
+        BBQHnswIndexOptions(int m, int efConstruction, RescoreVector rescoreVector) {
+            super(VectorIndexType.BBQ_HNSW, rescoreVector);
             this.m = m;
             this.efConstruction = efConstruction;
         }
@@ -1848,12 +1909,12 @@ public class DenseVectorFieldMapper extends FieldMapper {
         @Override
         boolean doEquals(IndexOptions other) {
             BBQHnswIndexOptions that = (BBQHnswIndexOptions) other;
-            return m == that.m && efConstruction == that.efConstruction;
+            return m == that.m && efConstruction == that.efConstruction && Objects.equals(rescoreVector, that.rescoreVector);
         }
 
         @Override
         int doHashCode() {
-            return Objects.hash(m, efConstruction);
+            return Objects.hash(m, efConstruction, rescoreVector);
         }
 
         @Override
@@ -1862,6 +1923,9 @@ public class DenseVectorFieldMapper extends FieldMapper {
             builder.field("type", type);
             builder.field("m", m);
             builder.field("ef_construction", efConstruction);
+            if (rescoreVector != null) {
+                rescoreVector.toXContent(builder, params);
+            }
             builder.endObject();
             return builder;
         }
@@ -1875,11 +1939,11 @@ public class DenseVectorFieldMapper extends FieldMapper {
         }
     }
 
-    static class BBQFlatIndexOptions extends IndexOptions {
+    static class BBQFlatIndexOptions extends QuantizedIndexOptions {
         private final int CLASS_NAME_HASH = this.getClass().getName().hashCode();
 
-        BBQFlatIndexOptions() {
-            super(VectorIndexType.BBQ_FLAT);
+        BBQFlatIndexOptions(RescoreVector rescoreVector) {
+            super(VectorIndexType.BBQ_FLAT, rescoreVector);
         }
 
         @Override
@@ -1907,6 +1971,9 @@ public class DenseVectorFieldMapper extends FieldMapper {
         public XContentBuilder toXContent(XContentBuilder builder, Params params) throws IOException {
             builder.startObject();
             builder.field("type", type);
+            if (rescoreVector != null) {
+                rescoreVector.toXContent(builder, params);
+            }
             builder.endObject();
             return builder;
         }
@@ -1920,6 +1987,41 @@ public class DenseVectorFieldMapper extends FieldMapper {
         }
     }
 
+    record RescoreVector(float oversample) implements ToXContentObject {
+        static final String NAME = "rescore_vector";
+        static final String OVERSAMPLE = "oversample";
+
+        static RescoreVector fromIndexOptions(Map<String, ?> indexOptionsMap) {
+            Object rescoreVectorNode = indexOptionsMap.remove(NAME);
+            if (rescoreVectorNode == null) {
+                return null;
+            }
+            Map<String, Object> mappedNode = XContentMapValues.nodeMapValue(rescoreVectorNode, NAME);
+            Object oversampleNode = mappedNode.get(OVERSAMPLE);
+            if (oversampleNode == null) {
+                throw new IllegalArgumentException("Invalid rescore_vector value. Missing required field " + OVERSAMPLE);
+            }
+            return new RescoreVector((float) XContentMapValues.nodeDoubleValue(oversampleNode));
+        }
+
+        RescoreVector {
+            if (oversample < 1) {
+                throw new IllegalArgumentException("oversample must be greater than 1");
+            }
+            if (oversample > 10) {
+                throw new IllegalArgumentException("oversample must be less than or equal to 10");
+            }
+        }
+
+        @Override
+        public XContentBuilder toXContent(XContentBuilder builder, Params params) throws IOException {
+            builder.startObject(NAME);
+            builder.field(OVERSAMPLE, oversample);
+            builder.endObject();
+            return builder;
+        }
+    }
+
     public static final TypeParser PARSER = new TypeParser(
         (n, c) -> new Builder(n, c.indexVersionCreated()),
         notInMultiFields(CONTENT_TYPE)
@@ -2135,7 +2237,7 @@ public class DenseVectorFieldMapper extends FieldMapper {
             float[] queryVector,
             int k,
             int numCands,
-            Float oversample,
+            Float queryOversample,
             Query filter,
             Float similarityThreshold,
             BitSetProducer parentFilter
@@ -2157,6 +2259,14 @@ public class DenseVectorFieldMapper extends FieldMapper {
             }
 
             int adjustedK = k;
+            // By default utilize the quantized oversample is configured
+            // allow the user provided at query time overwrite
+            Float oversample = queryOversample;
+            if (oversample == null
+                && indexOptions instanceof QuantizedIndexOptions quantizedIndexOptions
+                && quantizedIndexOptions.rescoreVector != null) {
+                oversample = quantizedIndexOptions.rescoreVector.oversample;
+            }
             boolean rescore = needsRescore(oversample);
             if (rescore) {
                 // Will get k * oversample for rescoring, and get the top k
@@ -2352,7 +2462,7 @@ public class DenseVectorFieldMapper extends FieldMapper {
         return new Builder(leafName(), indexCreatedVersion).init(this);
     }
 
-    private static IndexOptions parseIndexOptions(String fieldName, Object propNode) {
+    private static IndexOptions parseIndexOptions(String fieldName, Object propNode, IndexVersion indexVersion) {
         @SuppressWarnings("unchecked")
         Map<String, ?> indexOptionsMap = (Map<String, ?>) propNode;
         Object typeNode = indexOptionsMap.remove("type");
@@ -2365,7 +2475,7 @@ public class DenseVectorFieldMapper extends FieldMapper {
             throw new MapperParsingException("Unknown vector index options type [" + type + "] for field [" + fieldName + "]");
         }
         VectorIndexType parsedType = vectorIndexType.get();
-        return parsedType.parseIndexOptions(fieldName, indexOptionsMap);
+        return parsedType.parseIndexOptions(fieldName, indexOptionsMap, indexVersion);
     }
 
     /**

server/src/test/java/org/elasticsearch/index/mapper/vectors/DenseVectorFieldMapperTests.java

@@ -59,6 +59,7 @@ import java.io.IOException;
 import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.List;
+import java.util.Map;
 import java.util.Set;
 
 import static org.apache.lucene.codecs.lucene99.Lucene99HnswVectorsFormat.DEFAULT_BEAM_WIDTH;
@@ -883,6 +884,120 @@ public class DenseVectorFieldMapperTests extends MapperTestCase {
     @Override
     public void testAggregatableConsistency() {}
 
+    public void testRescoreVectorForNonQuantized() {
+        for (String indexType : List.of("hnsw", "flat")) {
+            Exception e = expectThrows(
+                MapperParsingException.class,
+                () -> createDocumentMapper(
+                    fieldMapping(
+                        b -> b.field("type", "dense_vector")
+                            .field("index", true)
+                            .startObject("index_options")
+                            .field("type", indexType)
+                            .field(DenseVectorFieldMapper.RescoreVector.NAME, Map.of("oversample", 1.5f))
+                            .endObject()
+                    )
+                )
+            );
+            e.getMessage().contains("Mapping definition for [field] has unsupported parameters:");
+        }
+    }
+
+    public void tesetRescoreVectorOldIndexVersion() {
+        IndexVersion incompatibleVersion = IndexVersionUtils.randomVersionBetween(
+            random(),
+            IndexVersionUtils.getLowestReadCompatibleVersion(),
+            IndexVersionUtils.getPreviousVersion(DenseVectorFieldMapper.ADD_RESCORE_PARAMS_TO_QUANTIZED_VECTORS)
+        );
+        for (String indexType : List.of("int8_hnsw", "int8_flat", "int4_hnsw", "int4_flat", "bbq_hnsw", "bbq_flat")) {
+            expectThrows(
+                MapperParsingException.class,
+                () -> createDocumentMapper(
+                    incompatibleVersion,
+                    fieldMapping(
+                        b -> b.field("type", "dense_vector")
+                            .field("index", true)
+                            .startObject("index_options")
+                            .field("type", indexType)
+                            .field(DenseVectorFieldMapper.RescoreVector.NAME, Map.of("oversample", 1.5f))
+                            .endObject()
+                    )
+                )
+            );
+        }
+    }
+
+    public void testInvalidRescoreVector() {
+        for (String indexType : List.of("int8_hnsw", "int8_flat", "int4_hnsw", "int4_flat", "bbq_hnsw", "bbq_flat")) {
+            Exception e = expectThrows(
+                MapperParsingException.class,
+                () -> createDocumentMapper(
+                    fieldMapping(
+                        b -> b.field("type", "dense_vector")
+                            .field("index", true)
+                            .startObject("index_options")
+                            .field("type", indexType)
+                            .field(DenseVectorFieldMapper.RescoreVector.NAME, Map.of("foo", 1.5f))
+                            .endObject()
+                    )
+                )
+            );
+            e.getMessage().contains("Invalid rescore_vector value. Missing required field oversample");
+            e = expectThrows(
+                MapperParsingException.class,
+                () -> createDocumentMapper(
+                    fieldMapping(
+                        b -> b.field("type", "dense_vector")
+                            .field("index", true)
+                            .startObject("index_options")
+                            .field("type", indexType)
+                            .field(DenseVectorFieldMapper.RescoreVector.NAME, Map.of("oversample", "foo"))
+                            .endObject()
+                    )
+                )
+            );
+            e = expectThrows(
+                MapperParsingException.class,
+                () -> createDocumentMapper(
+                    fieldMapping(
+                        b -> b.field("type", "dense_vector")
+                            .field("index", true)
+                            .startObject("index_options")
+                            .field("type", indexType)
+                            .field(DenseVectorFieldMapper.RescoreVector.NAME, Map.of("oversample", 0.1f))
+                            .endObject()
+                    )
+                )
+            );
+            e = expectThrows(
+                MapperParsingException.class,
+                () -> createDocumentMapper(
+                    fieldMapping(
+                        b -> b.field("type", "dense_vector")
+                            .field("index", true)
+                            .startObject("index_options")
+                            .field("type", indexType)
+                            .field(DenseVectorFieldMapper.RescoreVector.NAME, Map.of())
+                            .endObject()
+                    )
+                )
+            );
+            e = expectThrows(
+                MapperParsingException.class,
+                () -> createDocumentMapper(
+                    fieldMapping(
+                        b -> b.field("type", "dense_vector")
+                            .field("index", true)
+                            .startObject("index_options")
+                            .field("type", indexType)
+                            .field(DenseVectorFieldMapper.RescoreVector.NAME, Map.of("oversample", 10.1f))
+                            .endObject()
+                    )
+                )
+            );
+        }
+    }
+
     public void testDims() {
         {
             Exception e = expectThrows(MapperParsingException.class, () -> createMapperService(fieldMapping(b -> {

server/src/test/java/org/elasticsearch/index/mapper/vectors/DenseVectorFieldTypeTests.java

@@ -49,6 +49,10 @@ public class DenseVectorFieldTypeTests extends FieldTypeTestCase {
         this.indexed = randomBoolean();
     }
 
+    private static DenseVectorFieldMapper.RescoreVector randomRescoreVector() {
+        return new DenseVectorFieldMapper.RescoreVector(randomFloatBetween(1.0F, 10.0F, false));
+    }
+
     private DenseVectorFieldMapper.IndexOptions randomIndexOptionsNonQuantized() {
         return randomFrom(
             new DenseVectorFieldMapper.HnswIndexOptions(randomIntBetween(1, 100), randomIntBetween(1, 10_000)),
@@ -62,18 +66,30 @@ public class DenseVectorFieldTypeTests extends FieldTypeTestCase {
             new DenseVectorFieldMapper.Int8HnswIndexOptions(
                 randomIntBetween(1, 100),
                 randomIntBetween(1, 10_000),
-                randomFrom((Float) null, 0f, (float) randomDoubleBetween(0.9, 1.0, true))
+                randomFrom((Float) null, 0f, (float) randomDoubleBetween(0.9, 1.0, true)),
+                randomFrom((DenseVectorFieldMapper.RescoreVector) null, randomRescoreVector())
             ),
             new DenseVectorFieldMapper.Int4HnswIndexOptions(
                 randomIntBetween(1, 100),
                 randomIntBetween(1, 10_000),
-                randomFrom((Float) null, 0f, (float) randomDoubleBetween(0.9, 1.0, true))
+                randomFrom((Float) null, 0f, (float) randomDoubleBetween(0.9, 1.0, true)),
+                randomFrom((DenseVectorFieldMapper.RescoreVector) null, randomRescoreVector())
             ),
             new DenseVectorFieldMapper.FlatIndexOptions(),
-            new DenseVectorFieldMapper.Int8FlatIndexOptions(randomFrom((Float) null, 0f, (float) randomDoubleBetween(0.9, 1.0, true))),
-            new DenseVectorFieldMapper.Int4FlatIndexOptions(randomFrom((Float) null, 0f, (float) randomDoubleBetween(0.9, 1.0, true))),
-            new DenseVectorFieldMapper.BBQHnswIndexOptions(randomIntBetween(1, 100), randomIntBetween(1, 10_000)),
-            new DenseVectorFieldMapper.BBQFlatIndexOptions()
+            new DenseVectorFieldMapper.Int8FlatIndexOptions(
+                randomFrom((Float) null, 0f, (float) randomDoubleBetween(0.9, 1.0, true)),
+                randomFrom((DenseVectorFieldMapper.RescoreVector) null, randomRescoreVector())
+            ),
+            new DenseVectorFieldMapper.Int4FlatIndexOptions(
+                randomFrom((Float) null, 0f, (float) randomDoubleBetween(0.9, 1.0, true)),
+                randomFrom((DenseVectorFieldMapper.RescoreVector) null, randomRescoreVector())
+            ),
+            new DenseVectorFieldMapper.BBQHnswIndexOptions(
+                randomIntBetween(1, 100),
+                randomIntBetween(1, 10_000),
+                randomFrom((DenseVectorFieldMapper.RescoreVector) null, randomRescoreVector())
+            ),
+            new DenseVectorFieldMapper.BBQFlatIndexOptions(randomFrom((DenseVectorFieldMapper.RescoreVector) null, randomRescoreVector()))
         );
     }
 
@@ -82,14 +98,20 @@ public class DenseVectorFieldTypeTests extends FieldTypeTestCase {
             new DenseVectorFieldMapper.Int8HnswIndexOptions(
                 randomIntBetween(1, 100),
                 randomIntBetween(1, 10_000),
-                randomFrom((Float) null, 0f, (float) randomDoubleBetween(0.9, 1.0, true))
+                randomFrom((Float) null, 0f, (float) randomDoubleBetween(0.9, 1.0, true)),
+                randomFrom((DenseVectorFieldMapper.RescoreVector) null, randomRescoreVector())
             ),
             new DenseVectorFieldMapper.Int4HnswIndexOptions(
                 randomIntBetween(1, 100),
                 randomIntBetween(1, 10_000),
-                randomFrom((Float) null, 0f, (float) randomDoubleBetween(0.9, 1.0, true))
+                randomFrom((Float) null, 0f, (float) randomDoubleBetween(0.9, 1.0, true)),
+                randomFrom((DenseVectorFieldMapper.RescoreVector) null, randomRescoreVector())
             ),
-            new DenseVectorFieldMapper.BBQHnswIndexOptions(randomIntBetween(1, 100), randomIntBetween(1, 10_000))
+            new DenseVectorFieldMapper.BBQHnswIndexOptions(
+                randomIntBetween(1, 100),
+                randomIntBetween(1, 10_000),
+                randomFrom((DenseVectorFieldMapper.RescoreVector) null, randomRescoreVector())
+            )
         );
     }
 
@@ -195,6 +217,9 @@ public class DenseVectorFieldTypeTests extends FieldTypeTestCase {
                 queryVector[i] = randomFloat();
             }
             Query query = field.createKnnQuery(VectorData.fromFloats(queryVector), 10, 10, null, null, null, producer);
+            if (query instanceof RescoreKnnVectorQuery rescoreKnnVectorQuery) {
+                query = rescoreKnnVectorQuery.innerQuery();
+            }
             assertThat(query, instanceOf(DiversifyingChildrenFloatKnnVectorQuery.class));
         }
         {
@@ -346,6 +371,9 @@ public class DenseVectorFieldTypeTests extends FieldTypeTestCase {
                 queryVector[i] = randomFloat();
             }
             Query query = fieldWith4096dims.createKnnQuery(VectorData.fromFloats(queryVector), 10, 10, null, null, null, null);
+            if (query instanceof RescoreKnnVectorQuery rescoreKnnVectorQuery) {
+                query = rescoreKnnVectorQuery.innerQuery();
+            }
             assertThat(query, instanceOf(KnnFloatVectorQuery.class));
         }