diff --git a/javascript/sentry-conventions/src/attributes.ts b/javascript/sentry-conventions/src/attributes.ts
index 6a5bf0d0b..08a9a1a30 100644
--- a/javascript/sentry-conventions/src/attributes.ts
+++ b/javascript/sentry-conventions/src/attributes.ts
@@ -1155,7 +1155,7 @@ export type APP_NAME_TYPE = string;
  *
  * Aliases: {@link APP_VITALS_START_COLD_VALUE} `app.vitals.start.cold.value`
  *
- * @deprecated Use {@link APP_VITALS_START_COLD_VALUE} (app.vitals.start.cold.value) instead - Replaced by app.vitals.start.cold.value to align with the app.vitals.* namespace for mobile performance attributes
+ * @deprecated Use {@link APP_VITALS_START_VALUE} (app.vitals.start.value) instead - Replaced by app.vitals.start.value plus app.vitals.start.type
  * @example 1234.56
  */
 export const APP_START_COLD = 'app_start_cold';
@@ -1226,7 +1226,7 @@ export type APP_START_TYPE_TYPE = string;
  *
  * Aliases: {@link APP_VITALS_START_WARM_VALUE} `app.vitals.start.warm.value`
  *
- * @deprecated Use {@link APP_VITALS_START_WARM_VALUE} (app.vitals.start.warm.value) instead - Replaced by app.vitals.start.warm.value to align with the app.vitals.* namespace for mobile performance attributes
+ * @deprecated Use {@link APP_VITALS_START_VALUE} (app.vitals.start.value) instead - Replaced by app.vitals.start.value plus app.vitals.start.type
  * @example 1234.56
  */
 export const APP_START_WARM = 'app_start_warm';
@@ -1457,6 +1457,7 @@ export type APP_VITALS_STALL_PERCENTAGE_TYPE = number;
  *
  * Aliases: {@link APP_START_COLD} `app_start_cold`
  *
+ * @deprecated Use {@link APP_VITALS_START_VALUE} (app.vitals.start.value) instead - Replaced by app.vitals.start.value plus app.vitals.start.type. Cold and warm are not aliases of the unified value because they are mutually exclusive type-specific names.
  * @example 1234.56
  */
 export const APP_VITALS_START_COLD_VALUE = 'app.vitals.start.cold.value';
@@ -1552,6 +1553,27 @@ export const APP_VITALS_START_TYPE = 'app.vitals.start.type';
  */
 export type APP_VITALS_START_TYPE_TYPE = string;
 
+// Path: model/attributes/app/app__vitals__start__value.json
+
+/**
+ * The duration of an app start in milliseconds. Use with app.vitals.start.type to distinguish cold vs warm starts. `app.vitals.start.value`
+ *
+ * Attribute Value Type: `number` {@link APP_VITALS_START_VALUE_TYPE}
+ *
+ * Apply Scrubbing: manual
+ *
+ * Attribute defined in OTEL: No
+ * Visibility: public
+ *
+ * @example 1234.56
+ */
+export const APP_VITALS_START_VALUE = 'app.vitals.start.value';
+
+/**
+ * Type for {@link APP_VITALS_START_VALUE} app.vitals.start.value
+ */
+export type APP_VITALS_START_VALUE_TYPE = number;
+
 // Path: model/attributes/app/app__vitals__start__warm__value.json
 
 /**
@@ -1566,6 +1588,7 @@ export type APP_VITALS_START_TYPE_TYPE = string;
  *
  * Aliases: {@link APP_START_WARM} `app_start_warm`
  *
+ * @deprecated Use {@link APP_VITALS_START_VALUE} (app.vitals.start.value) instead - Replaced by app.vitals.start.value plus app.vitals.start.type. Cold and warm are not aliases of the unified value because they are mutually exclusive type-specific names.
  * @example 1234.56
  */
 export const APP_VITALS_START_WARM_VALUE = 'app.vitals.start.warm.value';
@@ -17769,6 +17792,7 @@ export const ATTRIBUTE_TYPE: Record<string, AttributeType> = {
   'app.vitals.start.reason': 'string',
   'app.vitals.start.screen': 'string',
   'app.vitals.start.type': 'string',
+  'app.vitals.start.value': 'double',
   'app.vitals.start.warm.value': 'double',
   'app.vitals.ttfd.value': 'double',
   'app.vitals.ttid.value': 'double',
@@ -18564,6 +18588,7 @@ export type AttributeName =
   | typeof APP_VITALS_START_REASON
   | typeof APP_VITALS_START_SCREEN
   | typeof APP_VITALS_START_TYPE
+  | typeof APP_VITALS_START_VALUE
   | typeof APP_VITALS_START_WARM_VALUE
   | typeof APP_VITALS_TTFD_VALUE
   | typeof APP_VITALS_TTID_VALUE
@@ -20162,7 +20187,7 @@ export const ATTRIBUTE_METADATA: Record<AttributeName, AttributeMetadata> = {
   app_start_cold: {
     brief: 'The duration of a cold app start in milliseconds',
     type: 'double',
-    keys: ['app.vitals.start.cold.value', 'app_start_cold'],
+    keys: ['app_start_cold'],
     applyScrubbing: {
       key: 'manual',
     },
@@ -20170,13 +20195,18 @@ export const ATTRIBUTE_METADATA: Record<AttributeName, AttributeMetadata> = {
     visibility: 'public',
     example: 1234.56,
     deprecation: {
-      replacement: 'app.vitals.start.cold.value',
-      reason:
-        'Replaced by app.vitals.start.cold.value to align with the app.vitals.* namespace for mobile performance attributes',
-      status: 'backfill',
+      replacement: 'app.vitals.start.value',
+      reason: 'Replaced by app.vitals.start.value plus app.vitals.start.type',
+      status: 'transform',
+      transformation: 'app_vitals_start_cold_warm_to_value',
     },
     aliases: ['app.vitals.start.cold.value'],
     changelog: [
+      {
+        version: 'next',
+        prs: [576],
+        description: 'Retargeted deprecation replacement to app.vitals.start.value via transform',
+      },
       { version: '0.5.0', prs: [323], description: 'Added and deprecated in favor of app.vitals.start.cold.value' },
     ],
   },
@@ -20219,7 +20249,7 @@ export const ATTRIBUTE_METADATA: Record<AttributeName, AttributeMetadata> = {
   app_start_warm: {
     brief: 'The duration of a warm app start in milliseconds',
     type: 'double',
-    keys: ['app.vitals.start.warm.value', 'app_start_warm'],
+    keys: ['app_start_warm'],
     applyScrubbing: {
       key: 'manual',
     },
@@ -20227,13 +20257,18 @@ export const ATTRIBUTE_METADATA: Record<AttributeName, AttributeMetadata> = {
     visibility: 'public',
     example: 1234.56,
     deprecation: {
-      replacement: 'app.vitals.start.warm.value',
-      reason:
-        'Replaced by app.vitals.start.warm.value to align with the app.vitals.* namespace for mobile performance attributes',
-      status: 'backfill',
+      replacement: 'app.vitals.start.value',
+      reason: 'Replaced by app.vitals.start.value plus app.vitals.start.type',
+      status: 'transform',
+      transformation: 'app_vitals_start_cold_warm_to_value',
     },
     aliases: ['app.vitals.start.warm.value'],
     changelog: [
+      {
+        version: 'next',
+        prs: [576],
+        description: 'Retargeted deprecation replacement to app.vitals.start.value via transform',
+      },
       { version: '0.5.0', prs: [323], description: 'Added and deprecated in favor of app.vitals.start.warm.value' },
     ],
   },
@@ -20373,15 +20408,29 @@ export const ATTRIBUTE_METADATA: Record<AttributeName, AttributeMetadata> = {
   'app.vitals.start.cold.value': {
     brief: 'The duration of a cold app start in milliseconds',
     type: 'double',
-    keys: ['app.vitals.start.cold.value', 'app_start_cold'],
+    keys: ['app.vitals.start.cold.value'],
     applyScrubbing: {
       key: 'manual',
     },
     isInOtel: false,
     visibility: 'public',
     example: 1234.56,
+    deprecation: {
+      replacement: 'app.vitals.start.value',
+      reason:
+        'Replaced by app.vitals.start.value plus app.vitals.start.type. Cold and warm are not aliases of the unified value because they are mutually exclusive type-specific names.',
+      status: 'transform',
+      transformation: 'app_vitals_start_cold_warm_to_value',
+    },
     aliases: ['app_start_cold'],
-    changelog: [{ version: '0.5.0', prs: [313], description: 'Added app.vitals.start.cold.value attribute' }],
+    changelog: [
+      {
+        version: 'next',
+        prs: [576],
+        description: 'Deprecated in favor of app.vitals.start.value plus app.vitals.start.type via transform',
+      },
+      { version: '0.5.0', prs: [313], description: 'Added app.vitals.start.cold.value attribute' },
+    ],
   },
   'app.vitals.start.prewarmed': {
     brief: 'Whether the app start was prewarmed.',
@@ -20433,18 +20482,51 @@ export const ATTRIBUTE_METADATA: Record<AttributeName, AttributeMetadata> = {
     aliases: ['app_start_type'],
     changelog: [{ version: '0.5.0', prs: [313], description: 'Added app.vitals.start.type attribute' }],
   },
+  'app.vitals.start.value': {
+    brief:
+      'The duration of an app start in milliseconds. Use with app.vitals.start.type to distinguish cold vs warm starts.',
+    type: 'double',
+    keys: ['app.vitals.start.value'],
+    applyScrubbing: {
+      key: 'manual',
+    },
+    isInOtel: false,
+    visibility: 'public',
+    example: 1234.56,
+    changelog: [
+      { version: 'next', prs: [576], description: 'Added app.vitals.start.value as the unified app start duration' },
+    ],
+    additionalContext: [
+      'Send this together with app.vitals.start.type (`cold` or `warm`). This replaces app.vitals.start.cold.value and app.vitals.start.warm.value.',
+      'Not aliased to the cold/warm attributes: those names are type-specific, not 1:1 copies of this key. Ingest derives this attribute (and type) from the older names via the app_vitals_start_cold_warm_to_value transformation.',
+    ],
+  },
   'app.vitals.start.warm.value': {
     brief: 'The duration of a warm app start in milliseconds',
     type: 'double',
-    keys: ['app.vitals.start.warm.value', 'app_start_warm'],
+    keys: ['app.vitals.start.warm.value'],
     applyScrubbing: {
       key: 'manual',
     },
     isInOtel: false,
     visibility: 'public',
     example: 1234.56,
+    deprecation: {
+      replacement: 'app.vitals.start.value',
+      reason:
+        'Replaced by app.vitals.start.value plus app.vitals.start.type. Cold and warm are not aliases of the unified value because they are mutually exclusive type-specific names.',
+      status: 'transform',
+      transformation: 'app_vitals_start_cold_warm_to_value',
+    },
     aliases: ['app_start_warm'],
-    changelog: [{ version: '0.5.0', prs: [313], description: 'Added app.vitals.start.warm.value attribute' }],
+    changelog: [
+      {
+        version: 'next',
+        prs: [576],
+        description: 'Deprecated in favor of app.vitals.start.value plus app.vitals.start.type via transform',
+      },
+      { version: '0.5.0', prs: [313], description: 'Added app.vitals.start.warm.value attribute' },
+    ],
   },
   'app.vitals.ttfd.value': {
     brief: 'The duration of time to full display in milliseconds',
@@ -31788,10 +31870,10 @@ export const ATTRIBUTE_SEARCH_METADATA: Record<string, AttributeSearchMetadata>
     deprecationChain: ['app.vitals.stall.percentage', 'stall_percentage'],
   },
   'app.vitals.start.cold.value': {
-    canonicalName: 'app.vitals.start.cold.value',
+    canonicalName: 'app.vitals.start.value',
     type: 'double',
     brief: 'The duration of a cold app start in milliseconds',
-    deprecationChain: ['app.vitals.start.cold.value', 'app_start_cold'],
+    deprecationChain: ['app.vitals.start.cold.value'],
   },
   'app.vitals.start.prewarmed': {
     canonicalName: 'app.vitals.start.prewarmed',
@@ -31818,11 +31900,18 @@ export const ATTRIBUTE_SEARCH_METADATA: Record<string, AttributeSearchMetadata>
     brief: 'The type of app start, for example `cold` or `warm`',
     deprecationChain: ['app.vitals.start.type', 'app_start_type'],
   },
+  'app.vitals.start.value': {
+    canonicalName: 'app.vitals.start.value',
+    type: 'double',
+    brief:
+      'The duration of an app start in milliseconds. Use with app.vitals.start.type to distinguish cold vs warm starts.',
+    deprecationChain: ['app.vitals.start.value'],
+  },
   'app.vitals.start.warm.value': {
-    canonicalName: 'app.vitals.start.warm.value',
+    canonicalName: 'app.vitals.start.value',
     type: 'double',
     brief: 'The duration of a warm app start in milliseconds',
-    deprecationChain: ['app.vitals.start.warm.value', 'app_start_warm'],
+    deprecationChain: ['app.vitals.start.warm.value'],
   },
   'app.vitals.ttfd.value': {
     canonicalName: 'app.vitals.ttfd.value',
@@ -31837,10 +31926,10 @@ export const ATTRIBUTE_SEARCH_METADATA: Record<string, AttributeSearchMetadata>
     deprecationChain: ['app.vitals.ttid.value', 'time_to_initial_display'],
   },
   app_start_cold: {
-    canonicalName: 'app.vitals.start.cold.value',
+    canonicalName: 'app.vitals.start.value',
     type: 'double',
     brief: 'The duration of a cold app start in milliseconds',
-    deprecationChain: ['app.vitals.start.cold.value', 'app_start_cold'],
+    deprecationChain: ['app_start_cold'],
   },
   app_start_type: {
     canonicalName: 'app.vitals.start.type',
@@ -31849,10 +31938,10 @@ export const ATTRIBUTE_SEARCH_METADATA: Record<string, AttributeSearchMetadata>
     deprecationChain: ['app.vitals.start.type', 'app_start_type'],
   },
   app_start_warm: {
-    canonicalName: 'app.vitals.start.warm.value',
+    canonicalName: 'app.vitals.start.value',
     type: 'double',
     brief: 'The duration of a warm app start in milliseconds',
-    deprecationChain: ['app.vitals.start.warm.value', 'app_start_warm'],
+    deprecationChain: ['app_start_warm'],
   },
   'art.gc.blocking_count': {
     canonicalName: 'art.gc.blocking_count',
@@ -36414,6 +36503,7 @@ export type Attributes = {
   [APP_VITALS_START_REASON]?: APP_VITALS_START_REASON_TYPE;
   [APP_VITALS_START_SCREEN]?: APP_VITALS_START_SCREEN_TYPE;
   [APP_VITALS_START_TYPE]?: APP_VITALS_START_TYPE_TYPE;
+  [APP_VITALS_START_VALUE]?: APP_VITALS_START_VALUE_TYPE;
   [APP_VITALS_START_WARM_VALUE]?: APP_VITALS_START_WARM_VALUE_TYPE;
   [APP_VITALS_TTFD_VALUE]?: APP_VITALS_TTFD_VALUE_TYPE;
   [APP_VITALS_TTID_VALUE]?: APP_VITALS_TTID_VALUE_TYPE;
diff --git a/model/attribute_transformations/app_vitals_start_cold_warm_to_value.json b/model/attribute_transformations/app_vitals_start_cold_warm_to_value.json
new file mode 100644
index 000000000..a1f5b2772
--- /dev/null
+++ b/model/attribute_transformations/app_vitals_start_cold_warm_to_value.json
@@ -0,0 +1,82 @@
+{
+  "id": "app_vitals_start_cold_warm_to_value",
+  "brief": "Derive unified app.vitals.start.value and app.vitals.start.type from the type-specific cold and warm duration attributes. Cold and warm are mutually exclusive, so they are not 1:1 aliases of the unified key.",
+  "inputs": [
+    {
+      "attribute": "app.vitals.start.cold.value",
+      "brief": "Deprecated cold app start duration."
+    },
+    {
+      "attribute": "app.vitals.start.warm.value",
+      "brief": "Deprecated warm app start duration."
+    },
+    {
+      "attribute": "app_start_cold",
+      "brief": "Legacy cold app start duration."
+    },
+    {
+      "attribute": "app_start_warm",
+      "brief": "Legacy warm app start duration."
+    }
+  ],
+  "outputs": [
+    {
+      "attribute": "app.vitals.start.value",
+      "brief": "Unified app start duration in milliseconds."
+    },
+    {
+      "attribute": "app.vitals.start.type",
+      "brief": "App start type, cold or warm."
+    }
+  ],
+  "actions": [
+    "If app.vitals.start.value is already present, keep it and do not overwrite it.",
+    "Prefer app.vitals.start.cold.value over app_start_cold, and app.vitals.start.warm.value over app_start_warm, when both a namespaced and a legacy name are present.",
+    "If a cold duration is present and app.vitals.start.value is missing, copy that duration to app.vitals.start.value and set app.vitals.start.type to \"cold\" when type is missing.",
+    "Otherwise, if a warm duration is present and app.vitals.start.value is missing, copy that duration to app.vitals.start.value and set app.vitals.start.type to \"warm\" when type is missing.",
+    "Do not copy a source duration that exceeds 180000 milliseconds.",
+    "Leave the source cold and warm attributes in place. Do not treat cold and warm as interchangeable copies of the unified key."
+  ],
+  "examples": [
+    {
+      "name": "cold namespaced duration",
+      "input": {
+        "app.vitals.start.cold.value": 1234.0
+      },
+      "output": {
+        "app.vitals.start.value": 1234.0,
+        "app.vitals.start.type": "cold"
+      }
+    },
+    {
+      "name": "warm namespaced duration",
+      "input": {
+        "app.vitals.start.warm.value": 567.0
+      },
+      "output": {
+        "app.vitals.start.value": 567.0,
+        "app.vitals.start.type": "warm"
+      }
+    },
+    {
+      "name": "legacy cold duration",
+      "input": {
+        "app_start_cold": 1234.0
+      },
+      "output": {
+        "app.vitals.start.value": 1234.0,
+        "app.vitals.start.type": "cold"
+      }
+    },
+    {
+      "name": "legacy warm duration",
+      "input": {
+        "app_start_warm": 567.0
+      },
+      "output": {
+        "app.vitals.start.value": 567.0,
+        "app.vitals.start.type": "warm"
+      }
+    }
+  ]
+}
diff --git a/model/attributes/app/app__vitals__start__cold__value.json b/model/attributes/app/app__vitals__start__cold__value.json
index 4614c8ec1..bb13b2626 100644
--- a/model/attributes/app/app__vitals__start__cold__value.json
+++ b/model/attributes/app/app__vitals__start__cold__value.json
@@ -8,8 +8,19 @@
   "is_in_otel": false,
   "example": 1234.56,
   "alias": ["app_start_cold"],
+  "deprecation": {
+    "replacement": "app.vitals.start.value",
+    "reason": "Replaced by app.vitals.start.value plus app.vitals.start.type. Cold and warm are not aliases of the unified value because they are mutually exclusive type-specific names.",
+    "_status": "transform",
+    "transformation": "app_vitals_start_cold_warm_to_value"
+  },
   "visibility": "public",
   "changelog": [
+    {
+      "version": "next",
+      "prs": [576],
+      "description": "Deprecated in favor of app.vitals.start.value plus app.vitals.start.type via transform"
+    },
     {
       "version": "0.5.0",
       "prs": [313],
diff --git a/model/attributes/app/app__vitals__start__value.json b/model/attributes/app/app__vitals__start__value.json
new file mode 100644
index 000000000..94710f00d
--- /dev/null
+++ b/model/attributes/app/app__vitals__start__value.json
@@ -0,0 +1,22 @@
+{
+  "key": "app.vitals.start.value",
+  "brief": "The duration of an app start in milliseconds. Use with app.vitals.start.type to distinguish cold vs warm starts.",
+  "type": "double",
+  "apply_scrubbing": {
+    "key": "manual"
+  },
+  "is_in_otel": false,
+  "example": 1234.56,
+  "visibility": "public",
+  "additional_context": [
+    "Send this together with app.vitals.start.type (`cold` or `warm`). This replaces app.vitals.start.cold.value and app.vitals.start.warm.value.",
+    "Not aliased to the cold/warm attributes: those names are type-specific, not 1:1 copies of this key. Ingest derives this attribute (and type) from the older names via the app_vitals_start_cold_warm_to_value transformation."
+  ],
+  "changelog": [
+    {
+      "version": "next",
+      "prs": [576],
+      "description": "Added app.vitals.start.value as the unified app start duration"
+    }
+  ]
+}
diff --git a/model/attributes/app/app__vitals__start__warm__value.json b/model/attributes/app/app__vitals__start__warm__value.json
index 824f023a2..5f662a28e 100644
--- a/model/attributes/app/app__vitals__start__warm__value.json
+++ b/model/attributes/app/app__vitals__start__warm__value.json
@@ -8,8 +8,19 @@
   "is_in_otel": false,
   "example": 1234.56,
   "alias": ["app_start_warm"],
+  "deprecation": {
+    "replacement": "app.vitals.start.value",
+    "reason": "Replaced by app.vitals.start.value plus app.vitals.start.type. Cold and warm are not aliases of the unified value because they are mutually exclusive type-specific names.",
+    "_status": "transform",
+    "transformation": "app_vitals_start_cold_warm_to_value"
+  },
   "visibility": "public",
   "changelog": [
+    {
+      "version": "next",
+      "prs": [576],
+      "description": "Deprecated in favor of app.vitals.start.value plus app.vitals.start.type via transform"
+    },
     {
       "version": "0.5.0",
       "prs": [313],
diff --git a/model/attributes/app_start_cold.json b/model/attributes/app_start_cold.json
index 0381aebe2..e1f2d010f 100644
--- a/model/attributes/app_start_cold.json
+++ b/model/attributes/app_start_cold.json
@@ -9,12 +9,18 @@
   "example": 1234.56,
   "alias": ["app.vitals.start.cold.value"],
   "deprecation": {
-    "replacement": "app.vitals.start.cold.value",
-    "reason": "Replaced by app.vitals.start.cold.value to align with the app.vitals.* namespace for mobile performance attributes",
-    "_status": "backfill"
+    "replacement": "app.vitals.start.value",
+    "reason": "Replaced by app.vitals.start.value plus app.vitals.start.type",
+    "_status": "transform",
+    "transformation": "app_vitals_start_cold_warm_to_value"
   },
   "visibility": "public",
   "changelog": [
+    {
+      "version": "next",
+      "prs": [576],
+      "description": "Retargeted deprecation replacement to app.vitals.start.value via transform"
+    },
     {
       "version": "0.5.0",
       "prs": [323],
diff --git a/model/attributes/app_start_warm.json b/model/attributes/app_start_warm.json
index a73587cac..070da7626 100644
--- a/model/attributes/app_start_warm.json
+++ b/model/attributes/app_start_warm.json
@@ -9,12 +9,18 @@
   "example": 1234.56,
   "alias": ["app.vitals.start.warm.value"],
   "deprecation": {
-    "replacement": "app.vitals.start.warm.value",
-    "reason": "Replaced by app.vitals.start.warm.value to align with the app.vitals.* namespace for mobile performance attributes",
-    "_status": "backfill"
+    "replacement": "app.vitals.start.value",
+    "reason": "Replaced by app.vitals.start.value plus app.vitals.start.type",
+    "_status": "transform",
+    "transformation": "app_vitals_start_cold_warm_to_value"
   },
   "visibility": "public",
   "changelog": [
+    {
+      "version": "next",
+      "prs": [576],
+      "description": "Retargeted deprecation replacement to app.vitals.start.value via transform"
+    },
     {
       "version": "0.5.0",
       "prs": [323],
diff --git a/model/measurements/app_start_cold.json b/model/measurements/app_start_cold.json
index 9b73fba0f..07fa90051 100644
--- a/model/measurements/app_start_cold.json
+++ b/model/measurements/app_start_cold.json
@@ -1,8 +1,8 @@
 {
   "key": "app_start_cold",
   "full_name": "App Start Cold",
-  "brief": "The time it takes for the app to start from a cold state",
+  "brief": "The time it takes for the app to start from a cold state. Corresponds to app.vitals.start.value when app.vitals.start.type is cold.",
   "unit": "millisecond",
   "platform": "mobile",
-  "attribute": "app.vitals.start.cold.value"
+  "attribute": "app.vitals.start.value"
 }
diff --git a/model/measurements/app_start_warm.json b/model/measurements/app_start_warm.json
index b62779c24..d38e6a613 100644
--- a/model/measurements/app_start_warm.json
+++ b/model/measurements/app_start_warm.json
@@ -1,8 +1,8 @@
 {
   "key": "app_start_warm",
   "full_name": "App Start Warm",
-  "brief": "The time it takes for the app to start from a warm state",
+  "brief": "The time it takes for the app to start from a warm state. Corresponds to app.vitals.start.value when app.vitals.start.type is warm.",
   "unit": "millisecond",
   "platform": "mobile",
-  "attribute": "app.vitals.start.warm.value"
+  "attribute": "app.vitals.start.value"
 }
diff --git a/python/src/sentry_conventions/attributes.py b/python/src/sentry_conventions/attributes.py
index e78a4b14d..795a5236a 100644
--- a/python/src/sentry_conventions/attributes.py
+++ b/python/src/sentry_conventions/attributes.py
@@ -197,6 +197,8 @@ class _AttributeNamesMeta(type):
         "APP_APP_NAME",
         "APP_APP_START_TIME",
         "APP_APP_VERSION",
+        "APP_VITALS_START_COLD_VALUE",
+        "APP_VITALS_START_WARM_VALUE",
         "APP_START_COLD",
         "APP_START_TYPE",
         "APP_START_WARM",
@@ -1151,6 +1153,7 @@ class ATTRIBUTE_NAMES(metaclass=_AttributeNamesMeta):
     Defined in OTEL: No
     Visibility: public
     Aliases: app_start_cold
+    DEPRECATED: Use app.vitals.start.value instead - Replaced by app.vitals.start.value plus app.vitals.start.type. Cold and warm are not aliases of the unified value because they are mutually exclusive type-specific names.
     Example: 1234.56
     """
 
@@ -1205,6 +1208,17 @@ class ATTRIBUTE_NAMES(metaclass=_AttributeNamesMeta):
     Example: "cold"
     """
 
+    # Path: model/attributes/app/app__vitals__start__value.json
+    APP_VITALS_START_VALUE: Literal["app.vitals.start.value"] = "app.vitals.start.value"
+    """The duration of an app start in milliseconds. Use with app.vitals.start.type to distinguish cold vs warm starts.
+
+    Type: float
+    Apply Scrubbing: manual
+    Defined in OTEL: No
+    Visibility: public
+    Example: 1234.56
+    """
+
     # Path: model/attributes/app/app__vitals__start__warm__value.json
     APP_VITALS_START_WARM_VALUE: Literal["app.vitals.start.warm.value"] = (
         "app.vitals.start.warm.value"
@@ -1216,6 +1230,7 @@ class ATTRIBUTE_NAMES(metaclass=_AttributeNamesMeta):
     Defined in OTEL: No
     Visibility: public
     Aliases: app_start_warm
+    DEPRECATED: Use app.vitals.start.value instead - Replaced by app.vitals.start.value plus app.vitals.start.type. Cold and warm are not aliases of the unified value because they are mutually exclusive type-specific names.
     Example: 1234.56
     """
 
@@ -1252,7 +1267,7 @@ class ATTRIBUTE_NAMES(metaclass=_AttributeNamesMeta):
     Defined in OTEL: No
     Visibility: public
     Aliases: app.vitals.start.cold.value
-    DEPRECATED: Use app.vitals.start.cold.value instead - Replaced by app.vitals.start.cold.value to align with the app.vitals.* namespace for mobile performance attributes
+    DEPRECATED: Use app.vitals.start.value instead - Replaced by app.vitals.start.value plus app.vitals.start.type
     Example: 1234.56
     """
 
@@ -1278,7 +1293,7 @@ class ATTRIBUTE_NAMES(metaclass=_AttributeNamesMeta):
     Defined in OTEL: No
     Visibility: public
     Aliases: app.vitals.start.warm.value
-    DEPRECATED: Use app.vitals.start.warm.value instead - Replaced by app.vitals.start.warm.value to align with the app.vitals.* namespace for mobile performance attributes
+    DEPRECATED: Use app.vitals.start.value instead - Replaced by app.vitals.start.value plus app.vitals.start.type
     Example: 1234.56
     """
 
@@ -11411,16 +11426,24 @@ class ATTRIBUTE_NAMES(metaclass=_AttributeNamesMeta):
     "app.vitals.start.cold.value": AttributeMetadata(
         brief="The duration of a cold app start in milliseconds",
         type=AttributeType.DOUBLE,
-        keys=(
-            "app.vitals.start.cold.value",
-            "app_start_cold",
-        ),
+        keys=("app.vitals.start.cold.value",),
         apply_scrubbing=ApplyScrubbingInfo(key=ApplyScrubbing.MANUAL),
         is_in_otel=False,
         visibility=Visibility.PUBLIC,
         example=1234.56,
+        deprecation=DeprecationInfo(
+            replacement="app.vitals.start.value",
+            reason="Replaced by app.vitals.start.value plus app.vitals.start.type. Cold and warm are not aliases of the unified value because they are mutually exclusive type-specific names.",
+            status=DeprecationStatus.TRANSFORM,
+            transformation="app_vitals_start_cold_warm_to_value",
+        ),
         aliases=["app_start_cold"],
         changelog=[
+            ChangelogEntry(
+                version="next",
+                prs=[576],
+                description="Deprecated in favor of app.vitals.start.value plus app.vitals.start.type via transform",
+            ),
             ChangelogEntry(
                 version="0.5.0",
                 prs=[313],
@@ -11496,19 +11519,47 @@ class ATTRIBUTE_NAMES(metaclass=_AttributeNamesMeta):
             ),
         ],
     ),
+    "app.vitals.start.value": AttributeMetadata(
+        brief="The duration of an app start in milliseconds. Use with app.vitals.start.type to distinguish cold vs warm starts.",
+        type=AttributeType.DOUBLE,
+        keys=("app.vitals.start.value",),
+        apply_scrubbing=ApplyScrubbingInfo(key=ApplyScrubbing.MANUAL),
+        is_in_otel=False,
+        visibility=Visibility.PUBLIC,
+        example=1234.56,
+        changelog=[
+            ChangelogEntry(
+                version="next",
+                prs=[576],
+                description="Added app.vitals.start.value as the unified app start duration",
+            ),
+        ],
+        additional_context=[
+            "Send this together with app.vitals.start.type (`cold` or `warm`). This replaces app.vitals.start.cold.value and app.vitals.start.warm.value.",
+            "Not aliased to the cold/warm attributes: those names are type-specific, not 1:1 copies of this key. Ingest derives this attribute (and type) from the older names via the app_vitals_start_cold_warm_to_value transformation.",
+        ],
+    ),
     "app.vitals.start.warm.value": AttributeMetadata(
         brief="The duration of a warm app start in milliseconds",
         type=AttributeType.DOUBLE,
-        keys=(
-            "app.vitals.start.warm.value",
-            "app_start_warm",
-        ),
+        keys=("app.vitals.start.warm.value",),
         apply_scrubbing=ApplyScrubbingInfo(key=ApplyScrubbing.MANUAL),
         is_in_otel=False,
         visibility=Visibility.PUBLIC,
         example=1234.56,
+        deprecation=DeprecationInfo(
+            replacement="app.vitals.start.value",
+            reason="Replaced by app.vitals.start.value plus app.vitals.start.type. Cold and warm are not aliases of the unified value because they are mutually exclusive type-specific names.",
+            status=DeprecationStatus.TRANSFORM,
+            transformation="app_vitals_start_cold_warm_to_value",
+        ),
         aliases=["app_start_warm"],
         changelog=[
+            ChangelogEntry(
+                version="next",
+                prs=[576],
+                description="Deprecated in favor of app.vitals.start.value plus app.vitals.start.type via transform",
+            ),
             ChangelogEntry(
                 version="0.5.0",
                 prs=[313],
@@ -11559,21 +11610,24 @@ class ATTRIBUTE_NAMES(metaclass=_AttributeNamesMeta):
     "app_start_cold": AttributeMetadata(
         brief="The duration of a cold app start in milliseconds",
         type=AttributeType.DOUBLE,
-        keys=(
-            "app.vitals.start.cold.value",
-            "app_start_cold",
-        ),
+        keys=("app_start_cold",),
         apply_scrubbing=ApplyScrubbingInfo(key=ApplyScrubbing.MANUAL),
         is_in_otel=False,
         visibility=Visibility.PUBLIC,
         example=1234.56,
         deprecation=DeprecationInfo(
-            replacement="app.vitals.start.cold.value",
-            reason="Replaced by app.vitals.start.cold.value to align with the app.vitals.* namespace for mobile performance attributes",
-            status=DeprecationStatus.BACKFILL,
+            replacement="app.vitals.start.value",
+            reason="Replaced by app.vitals.start.value plus app.vitals.start.type",
+            status=DeprecationStatus.TRANSFORM,
+            transformation="app_vitals_start_cold_warm_to_value",
         ),
         aliases=["app.vitals.start.cold.value"],
         changelog=[
+            ChangelogEntry(
+                version="next",
+                prs=[576],
+                description="Retargeted deprecation replacement to app.vitals.start.value via transform",
+            ),
             ChangelogEntry(
                 version="0.5.0",
                 prs=[323],
@@ -11611,21 +11665,24 @@ class ATTRIBUTE_NAMES(metaclass=_AttributeNamesMeta):
     "app_start_warm": AttributeMetadata(
         brief="The duration of a warm app start in milliseconds",
         type=AttributeType.DOUBLE,
-        keys=(
-            "app.vitals.start.warm.value",
-            "app_start_warm",
-        ),
+        keys=("app_start_warm",),
         apply_scrubbing=ApplyScrubbingInfo(key=ApplyScrubbing.MANUAL),
         is_in_otel=False,
         visibility=Visibility.PUBLIC,
         example=1234.56,
         deprecation=DeprecationInfo(
-            replacement="app.vitals.start.warm.value",
-            reason="Replaced by app.vitals.start.warm.value to align with the app.vitals.* namespace for mobile performance attributes",
-            status=DeprecationStatus.BACKFILL,
+            replacement="app.vitals.start.value",
+            reason="Replaced by app.vitals.start.value plus app.vitals.start.type",
+            status=DeprecationStatus.TRANSFORM,
+            transformation="app_vitals_start_cold_warm_to_value",
         ),
         aliases=["app.vitals.start.warm.value"],
         changelog=[
+            ChangelogEntry(
+                version="next",
+                prs=[576],
+                description="Retargeted deprecation replacement to app.vitals.start.value via transform",
+            ),
             ChangelogEntry(
                 version="0.5.0",
                 prs=[323],
@@ -24267,6 +24324,7 @@ class ATTRIBUTE_NAMES(metaclass=_AttributeNamesMeta):
         "app.vitals.start.reason": str,
         "app.vitals.start.screen": str,
         "app.vitals.start.type": str,
+        "app.vitals.start.value": float,
         "app.vitals.start.warm.value": float,
         "app.vitals.ttfd.value": float,
         "app.vitals.ttid.value": float,