diff --git a/.changeset/add-device-platform-exclude.md b/.changeset/add-device-platform-exclude.md
new file mode 100644
index 0000000000..0fc66c5c74
--- /dev/null
+++ b/.changeset/add-device-platform-exclude.md
@@ -0,0 +1,5 @@
+---
+"adcontextprotocol": minor
+---
+
+Add `targeting.device_platform_exclude` as the typed operating-system exclusion companion to `device_platform`, with exclude-wins and reject-rather-than-drop semantics.
diff --git a/docs/media-buy/advanced-topics/targeting.mdx b/docs/media-buy/advanced-topics/targeting.mdx
index 407f0efbf4..51a4274c39 100644
--- a/docs/media-buy/advanced-topics/targeting.mdx
+++ b/docs/media-buy/advanced-topics/targeting.mdx
@@ -485,10 +485,13 @@ Use for **technical requirements**:
 ```json
 {
   "$schema": "/schemas/core/targeting.json",
-  "device_platform": ["ios", "android"]
+  "device_platform": ["ios", "android"],
+  "device_platform_exclude": ["fire_os"]
 }
 ```
 
+Use `device_platform_exclude` when a campaign supports most platforms with a small deny-list. Exclusion wins if a value appears in both arrays. Device-platform inclusion and exclusion support are implied by `media_buy`; a seller that cannot enforce a requested platform constraint must reject it rather than broaden delivery.
+
 **Available platforms** (defined in [`device-platform.json`](https://adcontextprotocol.org/schemas/v3/enums/device-platform.json), based on Sec-CH-UA-Platform standard extended for CTV):
 - Browser: `ios`, `android`, `windows`, `macos`, `linux`, `chromeos`
 - CTV: `tvos`, `tizen`, `webos`, `fire_os`, `roku_os`
@@ -831,6 +834,14 @@ For products where inventory and audience planning are inseparable, such as line
 - **Use cases**: App install campaigns (iOS-only app), CTV-specific campaigns
 - **Values**: `ios`, `android`, `windows`, `macos`, `linux`, `chromeos`, `tvos`, `tizen`, `webos`, `fire_os`, `roku_os`
 
+### device_platform_exclude
+- **Description**: Exclude specific operating-system platforms from delivery
+- **Format**: Array of device platform identifiers
+- **Examples**: `["fire_os"]`, `["tvos", "roku_os"]`
+- **Use cases**: Exclude platforms incompatible with an app, landing experience, or creative runtime
+- **Conflict rule**: Exclusion wins when a platform is present in both `device_platform` and `device_platform_exclude`
+- **Note**: Support is implied by `media_buy`; sellers reject constraints they cannot enforce
+
 ### device_type
 - **Description**: Restrict to specific device form factors
 - **Format**: Array of device type identifiers
diff --git a/docs/protocol/get_adcp_capabilities.mdx b/docs/protocol/get_adcp_capabilities.mdx
index ecf8de5734..95fb0b447b 100644
--- a/docs/protocol/get_adcp_capabilities.mdx
+++ b/docs/protocol/get_adcp_capabilities.mdx
@@ -244,7 +244,7 @@ The following fields have been removed from the capabilities response:
 - `features.content_standards` — Replaced by `media_buy.content_standards` object. Presence of the object indicates support.
 - `features.audience_targeting` — Replaced by `media_buy.audience_targeting` object. Presence of the object indicates support.
 - `features.conversion_tracking` — Replaced by `media_buy.conversion_tracking` object. Presence of the object indicates support.
-- `execution.targeting.device_platform`, `device_type` — Implied by `media_buy` support.
+- `execution.targeting.device_platform`, `device_platform_exclude`, `device_type`, `device_type_exclude` — Implied by `media_buy` support.
 - `execution.targeting.audience_include`, `audience_exclude` — Implied by `audience_targeting` object presence.
 - `execution.trusted_match.supported` — Object presence indicates support.
 - `brand.identity` — Implied by `brand` in `supported_protocols`. `get_brand_identity` is always available.
diff --git a/static/schemas/source/core/targeting.json b/static/schemas/source/core/targeting.json
index 2d1bb5edc0..172f216a6a 100644
--- a/static/schemas/source/core/targeting.json
+++ b/static/schemas/source/core/targeting.json
@@ -210,6 +210,14 @@
       },
       "minItems": 1
     },
+    "device_platform_exclude": {
+      "type": "array",
+      "description": "Exclude specific operating-system platforms from delivery. Uses the same canonical device-platform vocabulary as device_platform. Exclusion wins when a platform appears in both include and exclude arrays. Support is implied by media_buy support; sellers MUST reject an exclusion they cannot enforce rather than silently dropping it.",
+      "items": {
+        "$ref": "/schemas/enums/device-platform.json"
+      },
+      "minItems": 1
+    },
     "device_type": {
       "type": "array",
       "description": "Restrict to specific device form factors. Use for campaigns targeting hardware categories rather than operating systems (e.g., mobile-only promotions, CTV campaigns).",
diff --git a/tests/device-platform-exclude.test.cjs b/tests/device-platform-exclude.test.cjs
new file mode 100644
index 0000000000..055166f396
--- /dev/null
+++ b/tests/device-platform-exclude.test.cjs
@@ -0,0 +1,25 @@
+const assert = require('node:assert/strict');
+const fs = require('node:fs');
+const path = require('node:path');
+const { describe, it } = require('node:test');
+
+const targeting = JSON.parse(fs.readFileSync(
+  path.join(__dirname, '..', 'static', 'schemas', 'source', 'core', 'targeting.json'),
+  'utf8',
+));
+
+describe('device_platform_exclude targeting overlay', () => {
+  it('uses the canonical device-platform enum with a non-empty array', () => {
+    const field = targeting.properties.device_platform_exclude;
+    assert.equal(field.type, 'array');
+    assert.equal(field.minItems, 1);
+    assert.equal(field.items.$ref, '/schemas/enums/device-platform.json');
+  });
+
+  it('pins exclude-wins and reject-rather-than-drop semantics', () => {
+    const description = targeting.properties.device_platform_exclude.description;
+    assert.match(description, /Exclusion wins/);
+    assert.match(description, /MUST reject/);
+    assert.match(description, /silently dropping/);
+  });
+});