diff --git a/package.json b/package.json
index 08e62e7..d4d08d3 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
   "name": "@unleash/client-specification",
-  "version": "5.1.9",
+  "version": "5.2.0",
   "description": "A collection of test specifications to guide client implementations in various languages",
   "scripts": {
     "test": "node index",
diff --git a/schema/delta-event-schema.js b/schema/delta-event-schema.js
new file mode 100644
index 0000000..e840181
--- /dev/null
+++ b/schema/delta-event-schema.js
@@ -0,0 +1,29 @@
+const Joi = require('joi');
+const featureSchema = require('./feature-schema');
+const segmentSchema = require('./segment-schema');
+
+const deltaEventSchema = Joi.alternatives().try(
+    Joi.object({
+        eventId: Joi.number().required(),
+        type: Joi.string().valid("hydration").required(),
+        segments: Joi.array().items(segmentSchema).optional(),
+        features: Joi.array().items(featureSchema).required(),
+    }),
+    Joi.object({
+        eventId: Joi.number().required(),
+        type: Joi.string().valid("feature-updated").required(),
+        feature: featureSchema.required(),
+    }),
+    Joi.object({
+        eventId: Joi.number().required(),
+        type: Joi.string().valid("feature-removed").required(),
+        featureName: Joi.string().required(),
+    }),
+    Joi.object({
+        eventId: Joi.number().required(),
+        type: Joi.string().valid("segment-updated").required(),
+        segment: segmentSchema.required(),
+    })
+);
+
+module.exports = deltaEventSchema;
diff --git a/schema/deltas-schema.js b/schema/deltas-schema.js
new file mode 100644
index 0000000..a84879c
--- /dev/null
+++ b/schema/deltas-schema.js
@@ -0,0 +1,8 @@
+const Joi = require('joi');
+const deltaEventSchema = require('./delta-event-schema.js');
+
+const deltasSchema = Joi.object({
+    events: Joi.array().items(deltaEventSchema).required(),
+});
+
+module.exports = deltasSchema;
\ No newline at end of file
diff --git a/schema/feature-schema.js b/schema/feature-schema.js
new file mode 100644
index 0000000..0c63dea
--- /dev/null
+++ b/schema/feature-schema.js
@@ -0,0 +1,67 @@
+const Joi = require('joi');
+
+const featureSchema = Joi.object().keys({
+    name: Joi.string().required(),
+    description: Joi.string().optional(),
+    enabled: Joi.boolean().required(),
+    project: Joi.string().optional(),
+    type: Joi.string().optional(),
+    description: Joi.string().optional().allow(null),
+    impressionData: Joi.boolean().optional(),
+    stale: Joi.boolean().optional(),
+    dependencies: Joi.array().optional().items(
+        Joi.object().keys({
+            feature: Joi.string().required(),
+            enabled: Joi.bool().optional(),
+            variants: Joi.array().items(Joi.string()).optional()
+        })
+    ),
+    segments: Joi.array().items(Joi.number()),
+    strategies: Joi.array().items(
+        Joi.object().keys({
+            name: Joi.string().required(),
+            parameters: Joi.object(),
+            variants: Joi.array().items(
+                Joi.object().keys({
+                    name: Joi.string().required(),
+                    payload: Joi.object().required().keys({
+                        type: Joi.string().required(),
+                        value: Joi.string().required().allow(""),
+                    }).optional(),
+                    weight: Joi.number().min(0).max(100000),
+                    stickiness: Joi.string().optional(),
+                })
+            ).optional(),
+            constraints: Joi.array().items(
+                Joi.object().keys({
+                    contextName: Joi.string().required(),
+                    operator: Joi.string().required(),
+                    values: Joi.array().items(Joi.string()),
+                    caseInsensitive: Joi.bool().optional(),
+                    inverted: Joi.bool().optional(),
+                    value: Joi.string().optional()
+                }).optional()
+            ),
+            segments: Joi.array().items(Joi.number()).optional()
+        })
+    ),
+    variants: Joi.array().items(
+        Joi.object().keys({
+            name: Joi.string().required(),
+            payload: Joi.object().required().keys({
+                type: Joi.string().required(),
+                value: Joi.string().required().allow(""),
+            }).optional(),
+            weight: Joi.number().min(0).max(100000),
+            stickiness: Joi.string().optional(),
+            overrides: Joi.array().items(
+                Joi.object().keys({
+                    contextName: Joi.string().required(),
+                    values: Joi.array().items(Joi.string()),
+                }).optional()
+            ),
+        })
+    )
+});
+
+module.exports = featureSchema;
diff --git a/schema/features-schema.js b/schema/features-schema.js
index c369a4a..2f20a1e 100644
--- a/schema/features-schema.js
+++ b/schema/features-schema.js
@@ -1,85 +1,11 @@
 const Joi = require('joi');
+const featureSchema = require('./feature-schema');
+const segmentSchema = require('./segment-schema');
 
-const schema = Joi.object().keys({
-    version: Joi.number()
-        .min(1)
-        .required(),
-    features: Joi.array().items(
-        Joi.object().keys({
-            name: Joi.string().required(),
-            description: Joi.string().optional(),
-            enabled: Joi.boolean().required(),
-            dependencies: Joi.array().optional().items(
-                Joi.object().keys({
-                    feature: Joi.string().required(),
-                    enabled: Joi.bool().optional(),
-                    variants: Joi.array().items(Joi.string()).optional()
-                })
-            ),
-            strategies: Joi.array().items(
-                Joi.object().keys({
-                    name: Joi.string().required(),
-                    parameters: Joi.object(),
-                    variants: Joi.array().items(
-                        Joi.object().keys({
-                            name: Joi.string().required(),
-                            payload: Joi.object().required().keys({
-                                type: Joi.string().required(),
-                                value: Joi.string().required().allow(""),
-                            }).optional(),
-                            weight: Joi.number().min(0).max(100000),
-                            stickiness: Joi.string().optional(),
-                        })).optional(),
-                    constraints: Joi.array().items(
-                        Joi.object().keys({
-                            contextName: Joi.string().required(),
-                            operator: Joi.string().required(),
-                            values: Joi.array().items(Joi.string()),
-                            caseInsensitive: Joi.bool().optional(),
-                            inverted: Joi.bool().optional(),
-                            value: Joi.string().optional()
-                        }).optional()
-                    ),
-                    segments: Joi.array().items(Joi.number()).optional()
-                })
-            ),
-            variants: Joi.array().items(
-                Joi.object().keys({
-                    name: Joi.string().required(),
-                    payload: Joi.object().required().keys({
-                        type: Joi.string().required(),
-                        value: Joi.string().required().allow(""),
-                    }).optional(),
-                    weight: Joi.number().min(0).max(100000),
-                    stickiness: Joi.string().optional(),
-                    overrides: Joi.array().items(
-                        Joi
-                            .object()
-                            .keys({
-                                contextName: Joi.string().required(),
-                                values: Joi.array().items(Joi.string()),
-                            })
-                            .optional()
-                    ),
-                })
-            )
-        })
-    ),
-    segments: Joi.array().items(
-        Joi.object().keys({
-            id: Joi.number().required(),
-            constraints: Joi.array().items(
-                Joi.object().keys({
-                    contextName: Joi.string().required(),
-                    operator: Joi.string().required(),
-                    values: Joi.array().items(Joi.string()),
-                    caseInsensitive: Joi.bool().optional(),
-                    inverted: Joi.bool().optional(),
-                    value: Joi.string().optional()
-                }).optional()
-            ),
-        }).optional()
-    )
+const featuresSchema = Joi.object().keys({
+    version: Joi.number().min(1).required(),
+    features: Joi.array().items(featureSchema),
+    segments: Joi.array().items(segmentSchema)
 });
 
-module.exports = schema;
+module.exports = featuresSchema;
\ No newline at end of file
diff --git a/schema/segment-schema.js b/schema/segment-schema.js
new file mode 100644
index 0000000..7f3b881
--- /dev/null
+++ b/schema/segment-schema.js
@@ -0,0 +1,18 @@
+const Joi = require('joi');
+
+const segmentSchema = Joi.object().keys({
+    id: Joi.number().required(),
+    name: Joi.string().optional().allow(null),
+    constraints: Joi.array().items(
+        Joi.object().keys({
+            contextName: Joi.string().required(),
+            operator: Joi.string().required(),
+            values: Joi.array().items(Joi.string()),
+            caseInsensitive: Joi.bool().optional(),
+            inverted: Joi.bool().optional(),
+            value: Joi.string().optional()
+        }).optional()
+    ),
+});
+
+module.exports = segmentSchema;
diff --git a/schema/test-case-schema.js b/schema/test-case-schema.js
index b0201dd..1d44127 100644
--- a/schema/test-case-schema.js
+++ b/schema/test-case-schema.js
@@ -1,10 +1,11 @@
 const Joi = require('joi');
 const featuresSchema = require('./features-schema.js');
+const deltasSchema = require('./deltas-schema.js');
 const contextSchema = require('./context-schema.js');
 
 const schema = Joi.object().keys({
     name: Joi.string(),
-    state: featuresSchema,
+    state: Joi.alternatives().try(featuresSchema, deltasSchema).required(),
     tests: Joi.array().items(
         Joi.object().keys({
             description: Joi.string().required(),
diff --git a/specifications/19-delta-api-hydration.json b/specifications/19-delta-api-hydration.json
new file mode 100644
index 0000000..cf49ed7
--- /dev/null
+++ b/specifications/19-delta-api-hydration.json
@@ -0,0 +1,67 @@
+{
+    "name": "19-delta-api-hydration",
+    "state": {
+        "events": [
+            {
+                "eventId": 1,
+                "type": "hydration",
+                "segments": [
+                    {
+                        "id": 1,
+                        "name": "delta.api.hydration.segment",
+                        "constraints": [
+                            {
+                                "values": [
+                                    "abc",
+                                    "edf",
+                                    "gbd"
+                                ],
+                                "inverted": false,
+                                "operator": "IN",
+                                "contextName": "appName",
+                                "caseInsensitive": false
+                            }
+                        ]
+                    }
+                ],
+                "features": [
+                    {
+                        "impressionData": false,
+                        "enabled": true,
+                        "name": "delta.api.hydration",
+                        "description": null,
+                        "project": "default",
+                        "stale": false,
+                        "type": "release",
+                        "variants": [],
+                        "segments": [
+                            1
+                        ],
+                        "strategies": [
+                            {
+                                "name": "flexibleRollout",
+                                "constraints": [],
+                                "parameters": {
+                                    "groupId": "delta.api.hydration",
+                                    "rollout": "100",
+                                    "stickiness": "default"
+                                },
+                                "variants": []
+                            }
+                        ]
+                    }
+                ]
+            }
+        ]
+    },
+    "tests": [
+        {
+            "description": "Hydration feature should be enabled when context criteria are met",
+            "context": {
+                "appName": "abc"
+            },
+            "toggleName": "delta.api.hydration",
+            "expectedResult": true
+        }
+    ]
+}
\ No newline at end of file
diff --git a/specifications/20-delta-api-events.json b/specifications/20-delta-api-events.json
new file mode 100644
index 0000000..24bdf46
--- /dev/null
+++ b/specifications/20-delta-api-events.json
@@ -0,0 +1,111 @@
+{
+    "name": "19-delta-api-hydration",
+    "state": {
+        "events": [
+            {
+                "eventId": 1,
+                "type": "feature-updated",
+                "feature": {
+                    "impressionData": false,
+                    "enabled": true,
+                    "name": "delta.api.events.updated.1",
+                    "description": null,
+                    "project": "default",
+                    "stale": false,
+                    "type": "release",
+                    "variants": [],
+                    "strategies": [
+                        {
+                            "name": "default"
+                        }
+                    ]
+                }
+            },
+            {
+                "eventId": 2,
+                "type": "feature-updated",
+                "feature": {
+                    "impressionData": false,
+                    "enabled": true,
+                    "name": "delta.api.events.updated.2",
+                    "description": null,
+                    "project": "default",
+                    "stale": false,
+                    "type": "release",
+                    "variants": [],
+                    "strategies": [
+                        {
+                            "name": "default"
+                        }
+                    ]
+                }
+            },
+            {
+                "eventId": 3,
+                "type": "feature-removed",
+                "featureName": "delta.api.events.updated.2"
+            },
+            {
+            "eventId": 4,
+            "type": "segment-updated",
+            "segment": {
+                "id": 1,
+                "name": "my-segment",
+                "constraints": [
+                        {
+                            "values": [
+                                "abc",
+                                "edf",
+                                "gbd"
+                            ],
+                            "inverted": false,
+                            "operator": "IN",
+                            "contextName": "appName",
+                            "caseInsensitive": false
+                        }
+                    ]
+                }
+            },
+            {
+                "eventId": 5,
+                "type": "feature-updated",
+                "feature": {
+                    "impressionData": false,
+                    "enabled": true,
+                    "name": "delta.api.events.updated.3",
+                    "description": null,
+                    "project": "default",
+                    "stale": false,
+                    "type": "release",
+                    "variants": [],
+                    "strategies": [
+                        {
+                            "name": "default",
+                            "segments": [1]
+                        }
+                    ]
+                }
+            }
+        ]
+    },
+    "tests": [
+        {
+            "description": "delta.api.events.updated.1 should be enabled",
+            "context": {},
+            "toggleName": "delta.api.events.updated.1",
+            "expectedResult": true
+        },
+        {
+            "description": "delta.api.events.updated.2 should be disabled",
+            "context": {},
+            "toggleName": "delta.api.events.updated.2",
+            "expectedResult": false
+        },
+        {
+            "description": "delta.api.events.updated.3 should be enabled with segment",
+            "context": { "appName": "abc" },
+            "toggleName": "delta.api.events.updated.3",
+            "expectedResult": true
+        }
+    ]
+}
diff --git a/specifications/index.json b/specifications/index.json
index 1f1a999..d2c446c 100644
--- a/specifications/index.json
+++ b/specifications/index.json
@@ -16,5 +16,7 @@
   "15-global-constraints.json",
   "16-strategy-variants.json",
   "17-dependent-features.json",
-  "18-utf8-flag-names.json"
-]
+  "18-utf8-flag-names.json",
+  "19-delta-api-hydration.json",
+  "20-delta-api-events.json"
+]
\ No newline at end of file