diff --git a/Makefile b/Makefile
index 49b9ba27e3..edeed7f06b 100644
--- a/Makefile
+++ b/Makefile
@@ -37,7 +37,7 @@ patch-oapi-templates: ## Patch oapi-codegen chi-middleware template with custom
 update-openapi: patch-oapi-templates ## Update OpenAPI spec
 	$(call print-target)
 	$(MAKE) -C api/spec generate
-	go generate ./api/...
+	go generate ./api/... ./openmeter/.../notificationevents
 
 .PHONY: generate-javascript-sdk
 generate-javascript-sdk: ## Generate JavaScript SDK
diff --git a/api/notificationevents/billing/openapi.yaml b/api/notificationevents/billing/openapi.yaml
new file mode 100644
index 0000000000..18eaaa71be
--- /dev/null
+++ b/api/notificationevents/billing/openapi.yaml
@@ -0,0 +1,63 @@
+openapi: 3.0.0
+info:
+  title: Billing.NotificationEvents
+  description: Notification Event contracts owned by the billing domain.
+  version: 0.0.0
+tags: []
+paths: {}
+components:
+  schemas:
+    BillingInvoiceCreatedV1Payload:
+      type: object
+      required:
+        - invoice_id
+        - customer_id
+        - status
+        - currency
+        - total
+      properties:
+        invoice_id:
+          allOf:
+            - $ref: "#/components/schemas/ULID"
+          description: Invoice that was created.
+        customer_id:
+          allOf:
+            - $ref: "#/components/schemas/ULID"
+          description: Customer the invoice belongs to.
+        status:
+          type: string
+          description: Invoice status at creation time.
+        currency:
+          allOf:
+            - $ref: "#/components/schemas/CurrencyCode"
+          description: Invoice currency.
+        total:
+          allOf:
+            - $ref: "#/components/schemas/Numeric"
+          description: Invoice total at creation time.
+      additionalProperties: false
+      description: |-
+        Payload of `v1.billing.invoice.created`.
+
+        The payload identifies the invoice and carries its state at creation time;
+        consumers fetch the full invoice through the API when they need it.
+    CurrencyCode:
+      type: string
+      minLength: 3
+      maxLength: 3
+      pattern: ^[A-Z]{3}$
+      description: |-
+        Three-letter [ISO4217](https://www.iso.org/iso-4217-currency-codes.html)
+        currency code. Custom three-letter currency codes are also supported for
+        convenience.
+      example: USD
+    Numeric:
+      type: string
+      pattern: ^\-?[0-9]+(\.[0-9]+)?$
+      description: Numeric represents an arbitrary precision number.
+    ULID:
+      type: string
+      pattern: ^[0-7][0-9A-HJKMNP-TV-Z]{25}$
+      description: ULID (Universally Unique Lexicographically Sortable Identifier).
+      title: ULID
+      example: 01G65Z755AFWAKHE12NY0CQ9FH
diff --git a/api/notificationevents/entitlement/openapi.yaml b/api/notificationevents/entitlement/openapi.yaml
new file mode 100644
index 0000000000..87953f9dc9
--- /dev/null
+++ b/api/notificationevents/entitlement/openapi.yaml
@@ -0,0 +1,94 @@
+openapi: 3.0.0
+info:
+  title: Entitlements.NotificationEvents
+  description: Notification Event contracts owned by the entitlements domain.
+  version: 0.0.0
+tags: []
+paths: {}
+components:
+  schemas:
+    EntitlementBalanceThreshold:
+      type: object
+      required:
+        - type
+        - value
+      properties:
+        type:
+          allOf:
+            - $ref: "#/components/schemas/EntitlementBalanceThresholdType"
+          description: Condition kind of the threshold.
+        value:
+          type: number
+          format: double
+          description: Threshold value, interpreted according to the threshold type.
+      additionalProperties: false
+      description: A single entitlement balance threshold.
+    EntitlementBalanceThresholdTriggeredV1Payload:
+      type: object
+      required:
+        - customer_id
+        - entitlement_id
+        - feature_key
+        - current_balance
+        - threshold
+      properties:
+        customer_id:
+          allOf:
+            - $ref: "#/components/schemas/ULID"
+          description: Customer owning the entitlement.
+        entitlement_id:
+          allOf:
+            - $ref: "#/components/schemas/ULID"
+          description: Entitlement whose balance crossed the threshold.
+        feature_key:
+          allOf:
+            - $ref: "#/components/schemas/ResourceKey"
+          description: Feature of the entitlement.
+        current_balance:
+          type: number
+          format: double
+          description: Balance at evaluation time.
+        threshold:
+          allOf:
+            - $ref: "#/components/schemas/EntitlementBalanceThreshold"
+          description: Threshold that was crossed.
+      additionalProperties: false
+      description: Payload of `v1.entitlement.balance_threshold.triggered`.
+    EntitlementBalanceThresholdTriggeredV1RuleConfig:
+      type: object
+      required:
+        - thresholds
+      properties:
+        thresholds:
+          type: array
+          items:
+            $ref: "#/components/schemas/EntitlementBalanceThreshold"
+          minItems: 1
+          description: Thresholds evaluated against the entitlement balance.
+        features:
+          type: array
+          items:
+            $ref: "#/components/schemas/ResourceKey"
+          description: Feature keys the Rule is limited to. All features when omitted.
+      additionalProperties: false
+      description: Rule configuration of `v1.entitlement.balance_threshold.triggered`.
+    EntitlementBalanceThresholdType:
+      type: string
+      enum:
+        - balance_at_or_below
+        - usage_percentage_at_or_above
+      description: Condition kind of an entitlement balance threshold.
+    ResourceKey:
+      type: string
+      minLength: 1
+      maxLength: 64
+      pattern: ^[a-z0-9]+(?:_[a-z0-9]+)*$
+      description: A key is a unique string that is used to identify a resource.
+      title: Resource Key
+      example: resource_key
+    ULID:
+      type: string
+      pattern: ^[0-7][0-9A-HJKMNP-TV-Z]{25}$
+      description: ULID (Universally Unique Lexicographically Sortable Identifier).
+      title: ULID
+      example: 01G65Z755AFWAKHE12NY0CQ9FH
diff --git a/api/spec/Makefile b/api/spec/Makefile
index ae4ec74067..3eb6a46f24 100644
--- a/api/spec/Makefile
+++ b/api/spec/Makefile
@@ -34,6 +34,7 @@ test: ## Run AIP TypeScript SDK and emitter tests
 	pnpm --filter @openmeter/api-spec-aip run test
 	pnpm run test:sdk:coverage
 	pnpm --filter @openmeter/typespec-typescript run check
+	pnpm --filter @openmeter/typespec-notification-events run test
 
 .PHONY: publish-aip-sdk
 publish-aip-sdk: ## Publish the AIP TypeScript SDK (@openmeter/client) to npm
diff --git a/api/spec/README.md b/api/spec/README.md
index 469e54abf3..5d987eb76e 100644
--- a/api/spec/README.md
+++ b/api/spec/README.md
@@ -23,3 +23,13 @@ The AIP package defines v3 metering and billing APIs in line with [Kong’s AIP
 
 - **OpenMeter** (`openmeter.tsp`): OpenMeter v3 API.
 - **Konnect** (`konnect.tsp`): Konnect metering & billing API, same surface with Konnect-specific auth and servers.
+
+---
+
+## Notification Event contracts (`packages/aip/src/<domain>/notification-events/`)
+
+The producing domain owns the payload, and for rule-produced events the Rule configuration, of each Notification Event type. It declares them in a `<Domain>.NotificationEvents` namespace, mapped to a Go package in `packages/aip/src/notification-events.tsp`. `make update-openapi` generates the Go structs, JSON Schemas and event type values into `openmeter/<domain>/notificationevents`, and the events-only OpenAPI spec into `api/notificationevents/<domain>/`.
+
+- A released contract is immutable. Change it by adding the next version (`v2.<name>`, `...V2Payload`) next to it, never by editing it in place. Nested types follow the same rule: a breaking change needs a new type. Reviewers enforce this; generation does not.
+- Payloads are dedicated models. They may use `Shared` types but must not reuse API resource models, so that API changes cannot change a contract.
+- [`packages/typespec-notification-events`](packages/typespec-notification-events) enforces the naming and `@id` conventions at compile time.
diff --git a/api/spec/packages/aip/oapi-codegen.notification-events.yaml b/api/spec/packages/aip/oapi-codegen.notification-events.yaml
new file mode 100644
index 0000000000..b8628a28f9
--- /dev/null
+++ b/api/spec/packages/aip/oapi-codegen.notification-events.yaml
@@ -0,0 +1,12 @@
+# yaml-language-server: $schema=https://raw.githubusercontent.com/oapi-codegen/oapi-codegen/HEAD/configuration-schema.json
+# Shared oapi-codegen configuration of every domain notificationevents package.
+# The generated go:generate directive in each package (generate.gen.go) passes
+# the package name (-package) and the output file (-o), so neither is set here.
+generate:
+  models: true
+compatibility:
+  disable-required-readonly-as-pointer: true
+  always-prefix-enum-values: true
+output-options:
+  nullable-type: true
+  skip-prune: true
diff --git a/api/spec/packages/aip/package.json b/api/spec/packages/aip/package.json
index c48d2b9674..5c6a65853a 100644
--- a/api/spec/packages/aip/package.json
+++ b/api/spec/packages/aip/package.json
@@ -3,7 +3,7 @@
   "version": "0.1.0",
   "type": "module",
   "scripts": {
-    "generate": "tsp compile --config tspconfig.yaml ./src && node ./scripts/flatten-allof.mjs ./output/definitions/metering-and-billing/v3/openapi.MeteringAndBilling.yaml && node ./scripts/seal-object-schemas.mjs ./output/definitions/metering-and-billing/v3/*.yaml",
+    "generate": "tsp compile --config tspconfig.yaml ./src && node ./scripts/flatten-allof.mjs ./output/definitions/metering-and-billing/v3/openapi.MeteringAndBilling.yaml && node ./scripts/seal-object-schemas.mjs ./output/definitions/metering-and-billing/v3/*.yaml && tsp compile --config tspconfig.notification-events.yaml ./src/notification-events.tsp && node ./scripts/generate-notification-events.mjs",
     "bundle": "openapi bundle output/definitions/metering-and-billing/v3/openapi.OpenMeter.yaml",
     "watch": "tsp compile --watch --config tspconfig.yaml ./src",
     "test": "node --test test/*.test.js",
@@ -19,6 +19,7 @@
   },
   "devDependencies": {
     "@openmeter/typespec-go": "workspace:*",
+    "@openmeter/typespec-notification-events": "workspace:*",
     "@openmeter/typespec-typescript": "workspace:*",
     "@redocly/cli": "2.40.0",
     "@types/node": "26.1.1",
diff --git a/api/spec/packages/aip/scripts/generate-notification-events.mjs b/api/spec/packages/aip/scripts/generate-notification-events.mjs
new file mode 100644
index 0000000000..9cfe558c4a
--- /dev/null
+++ b/api/spec/packages/aip/scripts/generate-notification-events.mjs
@@ -0,0 +1,84 @@
+// Generates the per-domain Notification Event artifacts and copies them into
+// the Go module.
+//
+// Run after `tsp compile --config tspconfig.notification-events.yaml`, which
+// emits the JSON Schemas, the generated Go files and manifest.json. For every @goPackage
+// namespace in the manifest this script:
+//   1. compiles a generated entry point that makes the namespace an OpenAPI
+//      service, producing the events-only OpenAPI document of its types;
+//   2. copies that document to its committed location under api/, and the
+//      emitted generate.gen.go, events.gen.go and JSON Schemas into the Go
+//      package directory. `go generate` then runs oapi-codegen through the
+//      directive in generate.gen.go, like every other oapi-codegen target.
+import { execFileSync } from 'node:child_process'
+import { cpSync, mkdirSync, readFileSync, rmSync, writeFileSync } from 'node:fs'
+import { dirname, join, relative, resolve } from 'node:path'
+import { fileURLToPath } from 'node:url'
+
+const pkgRoot = resolve(dirname(fileURLToPath(import.meta.url)), '..')
+const repoRoot = resolve(pkgRoot, '../../../..')
+const out = join(pkgRoot, 'output/notification-events')
+const manifest = JSON.parse(
+  readFileSync(join(out, '_go/manifest.json'), 'utf8'),
+)
+
+for (const entry of manifest) {
+  const entryDir = join(out, 'entries')
+  const entryFile = join(entryDir, `${entry.dir.replaceAll('/', '_')}.tsp`)
+  const openapiDir = join(out, 'openapi', entry.dir)
+  mkdirSync(entryDir, { recursive: true })
+  writeFileSync(
+    entryFile,
+    [
+      `import "${relative(entryDir, join(pkgRoot, 'src/notification-events.tsp'))}";`,
+      '',
+      `@@TypeSpec.service(${entry.namespace}, #{ title: "${entry.namespace}" });`,
+      '',
+    ].join('\n'),
+  )
+  execFileSync(
+    'tsp',
+    [
+      'compile',
+      '--config',
+      join(pkgRoot, 'tspconfig.notification-events-openapi.yaml'),
+      entryFile,
+      '--option',
+      `@typespec/openapi3.emitter-output-dir=${openapiDir}`,
+    ],
+    { cwd: pkgRoot, stdio: 'inherit' },
+  )
+  // Same post-processing as v3: oapi-codegen and kin-openapi need
+  // additionalProperties: false instead of the emitter's { not: {} }.
+  execFileSync(
+    'node',
+    [
+      join(pkgRoot, 'scripts/seal-object-schemas.mjs'),
+      join(openapiDir, 'openapi.yaml'),
+    ],
+    {
+      stdio: 'inherit',
+    },
+  )
+
+  const goDir = join(repoRoot, entry.dir)
+  mkdirSync(goDir, { recursive: true })
+  mkdirSync(dirname(join(repoRoot, entry.spec)), { recursive: true })
+  cpSync(join(openapiDir, 'openapi.yaml'), join(repoRoot, entry.spec))
+  cpSync(
+    join(out, '_go', entry.dir, 'generate.gen.go'),
+    join(goDir, 'generate.gen.go'),
+  )
+  rmSync(join(goDir, 'events.gen.go'), { force: true })
+  rmSync(join(goDir, 'schemas'), { recursive: true, force: true })
+  if (entry.schemas.length > 0) {
+    cpSync(
+      join(out, '_go', entry.dir, 'events.gen.go'),
+      join(goDir, 'events.gen.go'),
+    )
+    mkdirSync(join(goDir, 'schemas'))
+    for (const { source, target } of entry.schemas) {
+      cpSync(join(out, 'jsonschema', source), join(goDir, 'schemas', target))
+    }
+  }
+}
diff --git a/api/spec/packages/aip/src/billing/notification-events/index.tsp b/api/spec/packages/aip/src/billing/notification-events/index.tsp
new file mode 100644
index 0000000000..de42abb45f
--- /dev/null
+++ b/api/spec/packages/aip/src/billing/notification-events/index.tsp
@@ -0,0 +1 @@
+import "./invoice.tsp";
diff --git a/api/spec/packages/aip/src/billing/notification-events/invoice.tsp b/api/spec/packages/aip/src/billing/notification-events/invoice.tsp
new file mode 100644
index 0000000000..ebc32a3920
--- /dev/null
+++ b/api/spec/packages/aip/src/billing/notification-events/invoice.tsp
@@ -0,0 +1,48 @@
+import "@typespec/json-schema";
+import "@openmeter/typespec-notification-events";
+import "../../shared/index.tsp";
+
+using TypeSpec.JsonSchema;
+using NotificationCodegen;
+
+/**
+ * Notification Event contracts owned by the billing domain.
+ */
+namespace Billing.NotificationEvents;
+
+/**
+ * Payload of `v1.billing.invoice.created`.
+ *
+ * The payload identifies the invoice and carries its state at creation time;
+ * consumers fetch the full invoice through the API when they need it.
+ */
+@jsonSchema
+@id("v1.billing.invoice.created.payload")
+@eventType("v1.billing.invoice.created")
+@friendlyName("BillingInvoiceCreatedV1Payload")
+model InvoiceCreatedV1Payload {
+  /**
+   * Invoice that was created.
+   */
+  invoice_id: Shared.ULID;
+
+  /**
+   * Customer the invoice belongs to.
+   */
+  customer_id: Shared.ULID;
+
+  /**
+   * Invoice status at creation time.
+   */
+  status: string;
+
+  /**
+   * Invoice currency.
+   */
+  currency: Shared.CurrencyCode;
+
+  /**
+   * Invoice total at creation time.
+   */
+  total: Shared.Numeric;
+}
diff --git a/api/spec/packages/aip/src/entitlements/notification-events/balance-threshold.tsp b/api/spec/packages/aip/src/entitlements/notification-events/balance-threshold.tsp
new file mode 100644
index 0000000000..7c5e6e1d72
--- /dev/null
+++ b/api/spec/packages/aip/src/entitlements/notification-events/balance-threshold.tsp
@@ -0,0 +1,99 @@
+import "@typespec/json-schema";
+import "@openmeter/typespec-notification-events";
+import "../../shared/index.tsp";
+
+using TypeSpec.JsonSchema;
+using NotificationCodegen;
+
+/**
+ * Notification Event contracts owned by the entitlements domain.
+ */
+namespace Entitlements.NotificationEvents;
+
+/**
+ * Condition kind of an entitlement balance threshold.
+ */
+@friendlyName("EntitlementBalanceThresholdType")
+enum BalanceThresholdType {
+  /**
+   * Triggers when the remaining balance drops to or below the value.
+   */
+  BalanceAtOrBelow: "balance_at_or_below",
+
+  /**
+   * Triggers when the used percentage of the entitlement reaches the value.
+   */
+  UsagePercentageAtOrAbove: "usage_percentage_at_or_above",
+}
+
+/**
+ * A single entitlement balance threshold.
+ */
+@friendlyName("EntitlementBalanceThreshold")
+model BalanceThreshold {
+  /**
+   * Condition kind of the threshold.
+   */
+  type: BalanceThresholdType;
+
+  /**
+   * Threshold value, interpreted according to the threshold type.
+   */
+  value: float64;
+}
+
+/**
+ * Rule configuration of `v1.entitlement.balance_threshold.triggered`.
+ */
+@jsonSchema
+@id("v1.entitlement.balance_threshold.triggered.rule_config")
+@friendlyName("EntitlementBalanceThresholdTriggeredV1RuleConfig")
+model BalanceThresholdTriggeredV1RuleConfig {
+  /**
+   * Thresholds evaluated against the entitlement balance.
+   */
+  @minItems(1)
+  thresholds: BalanceThreshold[];
+
+  /**
+   * Feature keys the Rule is limited to. All features when omitted.
+   */
+  features?: Shared.ResourceKey[];
+}
+
+/**
+ * Payload of `v1.entitlement.balance_threshold.triggered`.
+ */
+@jsonSchema
+@id("v1.entitlement.balance_threshold.triggered.payload")
+@eventType(
+  "v1.entitlement.balance_threshold.triggered",
+  BalanceThresholdTriggeredV1RuleConfig
+)
+@friendlyName("EntitlementBalanceThresholdTriggeredV1Payload")
+model BalanceThresholdTriggeredV1Payload {
+  /**
+   * Customer owning the entitlement.
+   */
+  customer_id: Shared.ULID;
+
+  /**
+   * Entitlement whose balance crossed the threshold.
+   */
+  entitlement_id: Shared.ULID;
+
+  /**
+   * Feature of the entitlement.
+   */
+  feature_key: Shared.ResourceKey;
+
+  /**
+   * Balance at evaluation time.
+   */
+  current_balance: float64;
+
+  /**
+   * Threshold that was crossed.
+   */
+  threshold: BalanceThreshold;
+}
diff --git a/api/spec/packages/aip/src/entitlements/notification-events/index.tsp b/api/spec/packages/aip/src/entitlements/notification-events/index.tsp
new file mode 100644
index 0000000000..37dcdff455
--- /dev/null
+++ b/api/spec/packages/aip/src/entitlements/notification-events/index.tsp
@@ -0,0 +1 @@
+import "./balance-threshold.tsp";
diff --git a/api/spec/packages/aip/src/notification-events.tsp b/api/spec/packages/aip/src/notification-events.tsp
new file mode 100644
index 0000000000..22e53995ec
--- /dev/null
+++ b/api/spec/packages/aip/src/notification-events.tsp
@@ -0,0 +1,24 @@
+import "@openmeter/typespec-notification-events";
+// Common aliases the top-level Billing namespace and Shared depends on Common,
+// so every compilation touching Shared needs Billing in the program.
+import "./common/error.tsp";
+import "./common/pagination.tsp";
+import "./billing/index.tsp";
+import "./billing/notification-events/index.tsp";
+import "./entitlements/notification-events/index.tsp";
+
+using NotificationCodegen;
+
+// Maps every Notification Event namespace to the Go package generated from it.
+// Adding a producing domain means importing its notification-events folder and
+// adding one @@goPackage here; scripts/generate-notification-events.mjs picks
+// it up.
+@@goPackage(
+  Entitlements.NotificationEvents,
+  "github.com/openmeterio/openmeter/openmeter/entitlement/notificationevents"
+);
+
+@@goPackage(
+  Billing.NotificationEvents,
+  "github.com/openmeterio/openmeter/openmeter/billing/notificationevents"
+);
diff --git a/api/spec/packages/aip/tspconfig.notification-events-openapi.yaml b/api/spec/packages/aip/tspconfig.notification-events-openapi.yaml
new file mode 100644
index 0000000000..8f3871c87e
--- /dev/null
+++ b/api/spec/packages/aip/tspconfig.notification-events-openapi.yaml
@@ -0,0 +1,12 @@
+# Events-only OpenAPI document of one @goPackage namespace, the input of
+# oapi-codegen for the namespace's Go package. Driven by
+# scripts/generate-notification-events.mjs, which generates the entry point and
+# sets emitter-output-dir.
+emit:
+  - '@typespec/openapi3'
+options:
+  '@typespec/openapi3':
+    seal-object-schemas: true
+linter:
+  extends:
+    - '@openmeter/api-spec-aip/all'
diff --git a/api/spec/packages/aip/tspconfig.notification-events.yaml b/api/spec/packages/aip/tspconfig.notification-events.yaml
new file mode 100644
index 0000000000..47a493ff1e
--- /dev/null
+++ b/api/spec/packages/aip/tspconfig.notification-events.yaml
@@ -0,0 +1,27 @@
+# Notification Event contracts: JSON Schemas of Event payloads and Rule
+# configurations, the generated Go Event type files and the manifest consumed by
+# scripts/generate-notification-events.mjs.
+emit:
+  - '@typespec/json-schema'
+  - '@openmeter/typespec-notification-events'
+parameters:
+  base-dir:
+    default: '{cwd}'
+output-dir: '{base-dir}'
+options:
+  '@typespec/json-schema':
+    emitter-output-dir: '{output-dir}/output/notification-events/jsonschema'
+    file-type: json
+    seal-object-schemas: true
+  '@openmeter/typespec-notification-events':
+    # The leading underscore keeps Go tooling from treating the emitted .go
+    # files as packages of the root module.
+    emitter-output-dir: '{output-dir}/output/notification-events/_go'
+    module-path: 'github.com/openmeterio/openmeter'
+    eventtype-import-path: 'github.com/openmeterio/openmeter/openmeter/notification/v4'
+    # Repository-relative paths referenced by the generated go:generate directives.
+    oapi-codegen-config: 'api/spec/packages/aip/oapi-codegen.notification-events.yaml'
+    spec-dir: 'api/notificationevents'
+linter:
+  extends:
+    - '@openmeter/api-spec-aip/all'
diff --git a/api/spec/packages/typespec-notification-events/lib/index.js b/api/spec/packages/typespec-notification-events/lib/index.js
new file mode 100644
index 0000000000..15b059f0a7
--- /dev/null
+++ b/api/spec/packages/typespec-notification-events/lib/index.js
@@ -0,0 +1,282 @@
+import {
+  createTypeSpecLibrary,
+  emitFile,
+  getFriendlyName,
+  getNamespaceFullName,
+  paramMessage,
+  resolvePath,
+} from '@typespec/compiler'
+import { getId, isJsonSchemaDeclaration } from '@typespec/json-schema'
+import { posix } from 'node:path'
+
+export const $lib = createTypeSpecLibrary({
+  name: '@openmeter/typespec-notification-events',
+  diagnostics: {
+    'invalid-event-type': {
+      severity: 'error',
+      messages: {
+        default: paramMessage`Event type "${'eventType'}" must be v<version>.<name> with a positive version and at least two lowercase snake_case name segments.`,
+      },
+    },
+    'invalid-contract': {
+      severity: 'error',
+      messages: {
+        default: paramMessage`${'detail'}`,
+      },
+    },
+    'event-type-outside-go-package': {
+      severity: 'error',
+      messages: {
+        default:
+          'Event payloads must be declared directly in a namespace decorated with @goPackage.',
+      },
+    },
+  },
+  emitter: {
+    options: {
+      type: 'object',
+      additionalProperties: false,
+      properties: {
+        'module-path': { type: 'string' },
+        'eventtype-import-path': { type: 'string' },
+        'oapi-codegen-config': { type: 'string' },
+        'spec-dir': { type: 'string' },
+      },
+      required: [
+        'module-path',
+        'eventtype-import-path',
+        'oapi-codegen-config',
+        'spec-dir',
+      ],
+    },
+  },
+})
+
+const goPackageKey = $lib.createStateSymbol('goPackage')
+const eventTypeKey = $lib.createStateSymbol('eventType')
+
+// Canonical Event type: v<version>.<name>, where the name has at least two
+// lowercase snake_case segments (<resource>.<operation>).
+const eventTypePattern =
+  /^v([1-9][0-9]*)\.([a-z][a-z0-9_]*(?:\.[a-z][a-z0-9_]*)+)$/
+
+export const $decorators = {
+  NotificationCodegen: {
+    goPackage(context, target, path) {
+      context.program.stateMap(goPackageKey).set(target, { path })
+    },
+    eventType(context, target, eventType, ruleConfig) {
+      const match = eventTypePattern.exec(eventType)
+      if (!match) {
+        context.program.reportDiagnostic(
+          $lib.createDiagnostic({
+            code: 'invalid-event-type',
+            format: { eventType },
+            target: context.decoratorTarget,
+          }),
+        )
+        return
+      }
+      context.program.stateMap(eventTypeKey).set(target, {
+        eventType,
+        version: Number(match[1]),
+        name: match[2],
+        ruleConfig,
+      })
+    },
+  },
+}
+
+// The Go identifier oapi-codegen derives from the OpenAPI component name,
+// which the AIP linter requires to be set through @friendlyName.
+const goName = (program, type) => getFriendlyName(program, type) ?? type.name
+
+// Released contracts are immutable and identified by their canonical Event
+// type, so the contract roots carry it in every name: the JSON Schema $id
+// (<event type>.payload / <event type>.rule_config) and the friendly name
+// (...V<version>Payload / ...V<version>RuleConfig, sharing one stem).
+// Nested types stay unversioned; changing one requires a new type.
+export function $onValidate(program) {
+  const packages = program.stateMap(goPackageKey)
+  const invalid = (target, detail) =>
+    program.reportDiagnostic(
+      $lib.createDiagnostic({
+        code: 'invalid-contract',
+        format: { detail },
+        target,
+      }),
+    )
+
+  for (const [model, e] of program.stateMap(eventTypeKey)) {
+    if (!packages.has(model.namespace)) {
+      program.reportDiagnostic(
+        $lib.createDiagnostic({
+          code: 'event-type-outside-go-package',
+          target: model,
+        }),
+      )
+    }
+
+    const payload = goName(program, model)
+    const payloadSuffix = `V${e.version}Payload`
+    const hasPayloadSuffix = payload.endsWith(payloadSuffix)
+    if (!hasPayloadSuffix) {
+      invalid(
+        model,
+        `Payload ${payload} of ${e.eventType} must have a friendly name ending in ${payloadSuffix}.`,
+      )
+    }
+
+    const roots = [[model, `${e.eventType}.payload`]]
+    if (e.ruleConfig) {
+      roots.push([e.ruleConfig, `${e.eventType}.rule_config`])
+      // The expected name derives from the payload's, so it is only
+      // meaningful once the payload name itself is valid.
+      const expected = payload.replace(/Payload$/, 'RuleConfig')
+      if (hasPayloadSuffix && goName(program, e.ruleConfig) !== expected) {
+        invalid(
+          e.ruleConfig,
+          `Rule configuration of ${e.eventType} must have the friendly name ${expected}.`,
+        )
+      }
+    }
+    for (const [type, id] of roots) {
+      if (!isJsonSchemaDeclaration(program, type)) {
+        invalid(type, `${type.name} must be decorated with @jsonSchema.`)
+      }
+      if (getId(program, type) !== id) {
+        invalid(type, `${type.name} must be decorated with @id("${id}").`)
+      }
+    }
+  }
+}
+
+// Emits, under the emitter output directory:
+//   - <go package dir>/generate.gen.go for every @goPackage namespace, holding
+//     the go:generate directive that runs oapi-codegen on the package's
+//     events-only OpenAPI document with the shared configuration;
+//   - <go package dir>/events.gen.go for every package owning @eventType
+//     payloads: the Event type value and the embedded JSON Schemas;
+//   - manifest.json describing every @goPackage namespace, used by
+//     scripts/generate-notification-events.mjs to generate the events-only
+//     OpenAPI documents and copy them, the Go files and the schemas into the
+//     repository.
+//
+// Paths in options and in the manifest are relative to the repository root.
+export async function $onEmit(context) {
+  const program = context.program
+  const modulePath = context.options['module-path']
+  const eventTypeImportPath = context.options['eventtype-import-path']
+  const eventTypePkg = eventTypeImportPath.split('/').pop()
+  const oapiCodegenConfig = context.options['oapi-codegen-config']
+  const specDir = context.options['spec-dir']
+
+  const eventsByNamespace = new Map()
+  for (const [model, def] of program.stateMap(eventTypeKey)) {
+    const list = eventsByNamespace.get(model.namespace) ?? []
+    list.push({ model, ...def })
+    eventsByNamespace.set(model.namespace, list)
+  }
+
+  const manifest = []
+  for (const [ns, { path }] of program.stateMap(goPackageKey)) {
+    if (!path.startsWith(modulePath + '/')) {
+      throw new Error(`@goPackage path ${path} is outside module ${modulePath}`)
+    }
+    const dir = path.slice(modulePath.length + 1)
+    const pkgName = path.split('/').pop()
+    // openmeter/entitlement/notificationevents -> <spec-dir>/entitlement/openapi.yaml
+    const domain = dir.replace(/^openmeter\//, '').replace(/\/[^/]+$/, '')
+    const spec = posix.join(specDir, domain, 'openapi.yaml')
+    const header = [
+      '// Code generated by @openmeter/typespec-notification-events, DO NOT EDIT.',
+      '',
+      `package ${pkgName}`,
+      '',
+    ]
+
+    await emitFile(program, {
+      path: resolvePath(context.emitterOutputDir, dir, 'generate.gen.go'),
+      content: [
+        ...header,
+        [
+          '//go:generate go tool github.com/oapi-codegen/oapi-codegen/v2/cmd/oapi-codegen',
+          `-config ${posix.relative(dir, oapiCodegenConfig)}`,
+          `-package ${pkgName}`,
+          '-o payloads.gen.go',
+          posix.relative(dir, spec),
+        ].join(' '),
+        '',
+      ].join('\n'),
+    })
+
+    const schemas = []
+    const events = (eventsByNamespace.get(ns) ?? []).sort((a, b) =>
+      a.eventType.localeCompare(b.eventType),
+    )
+    if (events.length > 0) {
+      const lines = [
+        ...header,
+        'import (',
+        '\t_ "embed"',
+        '',
+        `\t"${eventTypeImportPath}"`,
+        ')',
+        '',
+      ]
+      for (const e of events) {
+        const payload = goName(program, e.model)
+        const stem = payload.replace(/Payload$/, '')
+        // @typespec/json-schema names files after the TypeSpec declaration;
+        // the copy into the Go package renames them after their $id.
+        const payloadSchema = `${e.eventType}.payload.json`
+        schemas.push({ source: `${e.model.name}.json`, target: payloadSchema })
+        lines.push(
+          `// ${stem}EventType is ${e.eventType}.`,
+          `var ${stem}EventType = ${eventTypePkg}.EventType{`,
+          `\tName:    "${e.name}",`,
+          `\tVersion: ${e.version},`,
+          '}',
+          '',
+          `// ${stem}PayloadJSONSchema is the JSON Schema (draft 2020-12) of ${payload}.`,
+          '//',
+          `//go:embed schemas/${payloadSchema}`,
+          `var ${stem}PayloadJSONSchema []byte`,
+          '',
+        )
+        if (e.ruleConfig) {
+          const ruleConfigSchema = `${e.eventType}.rule_config.json`
+          schemas.push({
+            source: `${e.ruleConfig.name}.json`,
+            target: ruleConfigSchema,
+          })
+          lines.push(
+            `// ${stem}RuleConfigJSONSchema is the JSON Schema (draft 2020-12) of`,
+            `// ${goName(program, e.ruleConfig)}, the Rule configuration of ${e.eventType}.`,
+            '//',
+            `//go:embed schemas/${ruleConfigSchema}`,
+            `var ${stem}RuleConfigJSONSchema []byte`,
+            '',
+          )
+        }
+      }
+      await emitFile(program, {
+        path: resolvePath(context.emitterOutputDir, dir, 'events.gen.go'),
+        content: lines.join('\n'),
+      })
+    }
+
+    manifest.push({
+      namespace: getNamespaceFullName(ns),
+      dir,
+      package: pkgName,
+      spec,
+      schemas,
+    })
+  }
+
+  await emitFile(program, {
+    path: resolvePath(context.emitterOutputDir, 'manifest.json'),
+    content: JSON.stringify(manifest, null, 2) + '\n',
+  })
+}
diff --git a/api/spec/packages/typespec-notification-events/lib/main.tsp b/api/spec/packages/typespec-notification-events/lib/main.tsp
new file mode 100644
index 0000000000..f392d1b096
--- /dev/null
+++ b/api/spec/packages/typespec-notification-events/lib/main.tsp
@@ -0,0 +1,32 @@
+import "./index.js";
+
+/**
+ * Decorators that drive Notification Event contract code generation: which Go
+ * package owns a TypeSpec namespace, and which payload models are Event types.
+ */
+namespace NotificationCodegen;
+
+/**
+ * Declares the Go package generated from every model, enum and union declared
+ * directly in the namespace.
+ *
+ * @param path Go import path of the package.
+ */
+extern dec goPackage(
+  target: TypeSpec.Reflection.Namespace,
+  path: valueof string
+);
+
+/**
+ * Declares the model as the payload of a canonical Notification Event type.
+ *
+ * @param eventType Canonical Event type, `v<version>.<name>`, e.g.
+ * `v1.entitlement.balance_threshold.triggered`.
+ * @param ruleConfig Rule configuration model; omitted for system Event types
+ * that no Rule can produce.
+ */
+extern dec eventType(
+  target: TypeSpec.Reflection.Model,
+  eventType: valueof string,
+  ruleConfig?: TypeSpec.Reflection.Model
+);
diff --git a/api/spec/packages/typespec-notification-events/package.json b/api/spec/packages/typespec-notification-events/package.json
new file mode 100644
index 0000000000..ab5df31f02
--- /dev/null
+++ b/api/spec/packages/typespec-notification-events/package.json
@@ -0,0 +1,25 @@
+{
+  "name": "@openmeter/typespec-notification-events",
+  "version": "0.0.1",
+  "private": true,
+  "type": "module",
+  "main": "lib/index.js",
+  "tspMain": "lib/main.tsp",
+  "exports": {
+    ".": {
+      "typespec": "./lib/main.tsp",
+      "default": "./lib/index.js"
+    }
+  },
+  "scripts": {
+    "test": "vitest --run"
+  },
+  "dependencies": {
+    "@typespec/compiler": "1.14.0",
+    "@typespec/json-schema": "1.14.0",
+    "@typespec/openapi": "1.14.0"
+  },
+  "devDependencies": {
+    "vitest": "4.1.10"
+  }
+}
diff --git a/api/spec/packages/typespec-notification-events/test/notification-events.test.js b/api/spec/packages/typespec-notification-events/test/notification-events.test.js
new file mode 100644
index 0000000000..7c50b1cd8c
--- /dev/null
+++ b/api/spec/packages/typespec-notification-events/test/notification-events.test.js
@@ -0,0 +1,189 @@
+import { resolvePath } from '@typespec/compiler'
+import {
+  createTester,
+  expectDiagnosticEmpty,
+  expectDiagnostics,
+} from '@typespec/compiler/testing'
+import { describe, expect, it } from 'vitest'
+
+const Tester = createTester(resolvePath(import.meta.dirname, '..'), {
+  libraries: [
+    '@typespec/json-schema',
+    '@openmeter/typespec-notification-events',
+  ],
+})
+  .importLibraries()
+  .using('TypeSpec.JsonSchema', 'NotificationCodegen')
+
+const lib = '@openmeter/typespec-notification-events'
+
+// A rule-produced Event type with every contract convention satisfied; each
+// test overrides one declaration to break exactly one convention.
+function contract({
+  goPackage = '@goPackage("github.com/example/mod/openmeter/widget/notificationevents")',
+  eventType = 'v1.widget.thing.happened',
+  payloadName = 'WidgetThingHappenedV1Payload',
+  payloadId = 'v1.widget.thing.happened.payload',
+  ruleConfigName = 'WidgetThingHappenedV1RuleConfig',
+  ruleConfigJsonSchema = '@jsonSchema',
+} = {}) {
+  return `
+    ${goPackage}
+    namespace Widget.NotificationEvents {
+      ${ruleConfigJsonSchema}
+      @id("v1.widget.thing.happened.rule_config")
+      @friendlyName("${ruleConfigName}")
+      model ThingHappenedV1RuleConfig {
+        limit: int32;
+      }
+
+      @jsonSchema
+      @id("${payloadId}")
+      @eventType("${eventType}", ThingHappenedV1RuleConfig)
+      @friendlyName("${payloadName}")
+      model ThingHappenedV1Payload {
+        thing_id: string;
+      }
+    }
+  `
+}
+
+describe('contract validation', () => {
+  it('accepts a contract that follows every convention', async () => {
+    expectDiagnosticEmpty(await Tester.diagnose(contract()))
+  })
+
+  it('rejects a malformed Event type', async () => {
+    const diagnostics = await Tester.diagnose(
+      contract({ eventType: 'widget.thing.happened' }),
+    )
+
+    expectDiagnostics(diagnostics, { code: `${lib}/invalid-event-type` })
+  })
+
+  it('rejects an Event type outside a @goPackage namespace', async () => {
+    const diagnostics = await Tester.diagnose(contract({ goPackage: '' }))
+
+    expectDiagnostics(diagnostics, {
+      code: `${lib}/event-type-outside-go-package`,
+    })
+  })
+
+  it('rejects a payload name without the version suffix and reports only that', async () => {
+    // The Rule configuration name is derived from the payload name, so a
+    // second diagnostic about it would name a wrong expectation.
+    const diagnostics = await Tester.diagnose(
+      contract({ payloadName: 'WidgetThingHappenedPayload' }),
+    )
+
+    expectDiagnostics(diagnostics, {
+      code: `${lib}/invalid-contract`,
+      message:
+        'Payload WidgetThingHappenedPayload of v1.widget.thing.happened must have a friendly name ending in V1Payload.',
+    })
+  })
+
+  it('rejects a Rule configuration name that does not match the payload', async () => {
+    const diagnostics = await Tester.diagnose(
+      contract({ ruleConfigName: 'WidgetThingRuleConfig' }),
+    )
+
+    expectDiagnostics(diagnostics, {
+      code: `${lib}/invalid-contract`,
+      message:
+        'Rule configuration of v1.widget.thing.happened must have the friendly name WidgetThingHappenedV1RuleConfig.',
+    })
+  })
+
+  it('rejects a contract root without @jsonSchema', async () => {
+    const diagnostics = await Tester.diagnose(
+      contract({ ruleConfigJsonSchema: '' }),
+    )
+
+    expectDiagnostics(diagnostics, {
+      code: `${lib}/invalid-contract`,
+      message: 'ThingHappenedV1RuleConfig must be decorated with @jsonSchema.',
+    })
+  })
+
+  it('rejects a contract root whose @id does not match its Event type', async () => {
+    const diagnostics = await Tester.diagnose(
+      contract({ payloadId: 'widget.thing.happened.payload' }),
+    )
+
+    expectDiagnostics(diagnostics, {
+      code: `${lib}/invalid-contract`,
+      message:
+        'ThingHappenedV1Payload must be decorated with @id("v1.widget.thing.happened.payload").',
+    })
+  })
+})
+
+describe('emitter', () => {
+  const EmitTester = Tester.emit(lib, {
+    'module-path': 'github.com/example/mod',
+    'eventtype-import-path': 'github.com/example/mod/openmeter/notification/v4',
+    'oapi-codegen-config': 'api/oapi-codegen.yaml',
+    'spec-dir': 'api/notificationevents',
+  })
+
+  it('emits the go:generate directive, Event types and manifest of a package', async () => {
+    const { outputs } = await EmitTester.compile(contract())
+
+    expect(outputs['openmeter/widget/notificationevents/generate.gen.go'])
+      .toBe(`// Code generated by @openmeter/typespec-notification-events, DO NOT EDIT.
+
+package notificationevents
+
+//go:generate go tool github.com/oapi-codegen/oapi-codegen/v2/cmd/oapi-codegen -config ../../../api/oapi-codegen.yaml -package notificationevents -o payloads.gen.go ../../../api/notificationevents/widget/openapi.yaml
+`)
+
+    expect(outputs['openmeter/widget/notificationevents/events.gen.go'])
+      .toBe(`// Code generated by @openmeter/typespec-notification-events, DO NOT EDIT.
+
+package notificationevents
+
+import (
+	_ "embed"
+
+	"github.com/example/mod/openmeter/notification/v4"
+)
+
+// WidgetThingHappenedV1EventType is v1.widget.thing.happened.
+var WidgetThingHappenedV1EventType = v4.EventType{
+	Name:    "widget.thing.happened",
+	Version: 1,
+}
+
+// WidgetThingHappenedV1PayloadJSONSchema is the JSON Schema (draft 2020-12) of WidgetThingHappenedV1Payload.
+//
+//go:embed schemas/v1.widget.thing.happened.payload.json
+var WidgetThingHappenedV1PayloadJSONSchema []byte
+
+// WidgetThingHappenedV1RuleConfigJSONSchema is the JSON Schema (draft 2020-12) of
+// WidgetThingHappenedV1RuleConfig, the Rule configuration of v1.widget.thing.happened.
+//
+//go:embed schemas/v1.widget.thing.happened.rule_config.json
+var WidgetThingHappenedV1RuleConfigJSONSchema []byte
+`)
+
+    expect(JSON.parse(outputs['manifest.json'])).toEqual([
+      {
+        namespace: 'Widget.NotificationEvents',
+        dir: 'openmeter/widget/notificationevents',
+        package: 'notificationevents',
+        spec: 'api/notificationevents/widget/openapi.yaml',
+        schemas: [
+          {
+            source: 'ThingHappenedV1Payload.json',
+            target: 'v1.widget.thing.happened.payload.json',
+          },
+          {
+            source: 'ThingHappenedV1RuleConfig.json',
+            target: 'v1.widget.thing.happened.rule_config.json',
+          },
+        ],
+      },
+    ])
+  })
+})
diff --git a/api/spec/pnpm-lock.yaml b/api/spec/pnpm-lock.yaml
index 72e121e9d1..adf68f73fd 100644
--- a/api/spec/pnpm-lock.yaml
+++ b/api/spec/pnpm-lock.yaml
@@ -54,6 +54,9 @@ importers:
       '@openmeter/typespec-go':
         specifier: workspace:*
         version: link:../typespec-go
+      '@openmeter/typespec-notification-events':
+        specifier: workspace:*
+        version: link:../typespec-notification-events
       '@openmeter/typespec-typescript':
         specifier: workspace:*
         version: link:../typespec-typescript
@@ -180,6 +183,22 @@ importers:
         specifier: 4.1.12
         version: 4.1.12(@types/node@26.1.1)(@vitest/coverage-v8@4.1.12)(vite@8.1.6(@types/node@26.1.1)(esbuild@0.28.1)(tsx@4.23.1)(yaml@2.9.0))
 
+  packages/typespec-notification-events:
+    dependencies:
+      '@typespec/compiler':
+        specifier: 1.14.0
+        version: 1.14.0(patch_hash=4ba2da18fa7e2cd90e9c499debf14fc53ec5b6abae9eb2f5ddcb0c2eb52c0717)(@types/node@26.1.1)
+      '@typespec/json-schema':
+        specifier: 1.14.0
+        version: 1.14.0(@typespec/compiler@1.14.0(patch_hash=4ba2da18fa7e2cd90e9c499debf14fc53ec5b6abae9eb2f5ddcb0c2eb52c0717)(@types/node@26.1.1))
+      '@typespec/openapi':
+        specifier: 1.14.0
+        version: 1.14.0(patch_hash=a717b240dcdc3d23f8b752d783844b65ef750bad173549d92db12a5a0131183c)(@typespec/compiler@1.14.0(patch_hash=4ba2da18fa7e2cd90e9c499debf14fc53ec5b6abae9eb2f5ddcb0c2eb52c0717)(@types/node@26.1.1))(@typespec/http@1.14.0(patch_hash=2c55262cf42b2d54e5db3b8fe28abb4ab702cf9dbf34b5650c367270ec6ee5ef)(@typespec/compiler@1.14.0(patch_hash=4ba2da18fa7e2cd90e9c499debf14fc53ec5b6abae9eb2f5ddcb0c2eb52c0717)(@types/node@26.1.1))(@typespec/streams@0.84.0(@typespec/compiler@1.14.0(patch_hash=4ba2da18fa7e2cd90e9c499debf14fc53ec5b6abae9eb2f5ddcb0c2eb52c0717)(@types/node@26.1.1))))
+    devDependencies:
+      vitest:
+        specifier: 4.1.10
+        version: 4.1.10(@types/node@26.1.1)(@vitest/coverage-v8@4.1.10)(vite@8.0.16(@types/node@26.1.1)(esbuild@0.28.1)(tsx@4.23.1)(yaml@2.9.0))
+
   packages/typespec-typescript:
     dependencies:
       '@alloy-js/core':
diff --git a/go.mod b/go.mod
index 608ae69b7c..57fa548a2d 100644
--- a/go.mod
+++ b/go.mod
@@ -69,6 +69,7 @@ require (
 	github.com/samber/lo v1.53.0
 	github.com/samber/mo v1.17.0
 	github.com/samber/slog-multi v1.8.0
+	github.com/santhosh-tekuri/jsonschema/v6 v6.0.3
 	github.com/shopspring/decimal v1.5.0
 	github.com/spf13/cobra v1.10.2
 	github.com/spf13/pflag v1.0.10
@@ -187,7 +188,6 @@ require (
 	github.com/robfig/cron/v3 v3.0.1 // indirect
 	github.com/sagikazarmark/locafero v0.11.0 // indirect
 	github.com/samber/slog-common v0.21.0 // indirect
-	github.com/santhosh-tekuri/jsonschema/v6 v6.0.3 // indirect
 	github.com/segmentio/asm v1.2.1 // indirect
 	github.com/sergi/go-diff v1.4.0 // indirect
 	github.com/sony/gobreaker v1.0.0 // indirect
diff --git a/openmeter/billing/notificationevents/events.gen.go b/openmeter/billing/notificationevents/events.gen.go
new file mode 100644
index 0000000000..3c29c04dbd
--- /dev/null
+++ b/openmeter/billing/notificationevents/events.gen.go
@@ -0,0 +1,20 @@
+// Code generated by @openmeter/typespec-notification-events, DO NOT EDIT.
+
+package notificationevents
+
+import (
+	_ "embed"
+
+	"github.com/openmeterio/openmeter/openmeter/notification/v4"
+)
+
+// BillingInvoiceCreatedV1EventType is v1.billing.invoice.created.
+var BillingInvoiceCreatedV1EventType = v4.EventType{
+	Name:    "billing.invoice.created",
+	Version: 1,
+}
+
+// BillingInvoiceCreatedV1PayloadJSONSchema is the JSON Schema (draft 2020-12) of BillingInvoiceCreatedV1Payload.
+//
+//go:embed schemas/v1.billing.invoice.created.payload.json
+var BillingInvoiceCreatedV1PayloadJSONSchema []byte
diff --git a/openmeter/billing/notificationevents/events_test.go b/openmeter/billing/notificationevents/events_test.go
new file mode 100644
index 0000000000..15b14ebf51
--- /dev/null
+++ b/openmeter/billing/notificationevents/events_test.go
@@ -0,0 +1,41 @@
+package notificationevents
+
+import (
+	"bytes"
+	"encoding/json"
+	"testing"
+
+	"github.com/santhosh-tekuri/jsonschema/v6"
+	"github.com/stretchr/testify/require"
+)
+
+func TestInvoiceCreatedContract(t *testing.T) {
+	require.Equal(t, "v1.billing.invoice.created", BillingInvoiceCreatedV1EventType.String())
+	require.NoError(t, BillingInvoiceCreatedV1EventType.Validate())
+
+	// given the schema generated from the same TypeSpec model as the struct
+	doc, err := jsonschema.UnmarshalJSON(bytes.NewReader(BillingInvoiceCreatedV1PayloadJSONSchema))
+	require.NoError(t, err)
+
+	c := jsonschema.NewCompiler()
+	require.NoError(t, c.AddResource("schema.json", doc))
+
+	schema, err := c.Compile("schema.json")
+	require.NoError(t, err)
+
+	// when business logic marshals the generated struct
+	raw, err := json.Marshal(BillingInvoiceCreatedV1Payload{
+		InvoiceId:  "01J2KNAG7SY9X6V8E5P4D3C2ZF",
+		CustomerId: "01J2KNBH8TZ0Y7W9F6Q5E4D3AG",
+		Status:     "draft",
+		Currency:   "USD",
+		Total:      "12.50",
+	})
+	require.NoError(t, err)
+
+	payload, err := jsonschema.UnmarshalJSON(bytes.NewReader(raw))
+	require.NoError(t, err)
+
+	// then the schema accepts it
+	require.NoError(t, schema.Validate(payload))
+}
diff --git a/openmeter/billing/notificationevents/generate.gen.go b/openmeter/billing/notificationevents/generate.gen.go
new file mode 100644
index 0000000000..f081f046fb
--- /dev/null
+++ b/openmeter/billing/notificationevents/generate.gen.go
@@ -0,0 +1,5 @@
+// Code generated by @openmeter/typespec-notification-events, DO NOT EDIT.
+
+package notificationevents
+
+//go:generate go tool github.com/oapi-codegen/oapi-codegen/v2/cmd/oapi-codegen -config ../../../api/spec/packages/aip/oapi-codegen.notification-events.yaml -package notificationevents -o payloads.gen.go ../../../api/notificationevents/billing/openapi.yaml
diff --git a/openmeter/billing/notificationevents/notificationevents.go b/openmeter/billing/notificationevents/notificationevents.go
new file mode 100644
index 0000000000..a4bff9809d
--- /dev/null
+++ b/openmeter/billing/notificationevents/notificationevents.go
@@ -0,0 +1,5 @@
+// Package notificationevents contains the Notification Event contracts owned
+// by the billing domain. Everything else in it is generated from
+// api/spec/packages/aip/src/billing/notification-events; run `make gen-api`
+// after changing the TypeSpec.
+package notificationevents
diff --git a/openmeter/billing/notificationevents/payloads.gen.go b/openmeter/billing/notificationevents/payloads.gen.go
new file mode 100644
index 0000000000..7285644806
--- /dev/null
+++ b/openmeter/billing/notificationevents/payloads.gen.go
@@ -0,0 +1,36 @@
+// Package notificationevents provides primitives to interact with the openapi HTTP API.
+//
+// Code generated by github.com/oapi-codegen/oapi-codegen/v2 version v2.7.1 DO NOT EDIT.
+package notificationevents
+
+// BillingInvoiceCreatedV1Payload Payload of `v1.billing.invoice.created`.
+//
+// The payload identifies the invoice and carries its state at creation time;
+// consumers fetch the full invoice through the API when they need it.
+type BillingInvoiceCreatedV1Payload struct {
+	// Currency Invoice currency.
+	Currency CurrencyCode `json:"currency"`
+
+	// CustomerId Customer the invoice belongs to.
+	CustomerId ULID `json:"customer_id"`
+
+	// InvoiceId Invoice that was created.
+	InvoiceId ULID `json:"invoice_id"`
+
+	// Status Invoice status at creation time.
+	Status string `json:"status"`
+
+	// Total Invoice total at creation time.
+	Total Numeric `json:"total"`
+}
+
+// CurrencyCode Three-letter [ISO4217](https://www.iso.org/iso-4217-currency-codes.html)
+// currency code. Custom three-letter currency codes are also supported for
+// convenience.
+type CurrencyCode = string
+
+// Numeric Numeric represents an arbitrary precision number.
+type Numeric = string
+
+// ULID ULID (Universally Unique Lexicographically Sortable Identifier).
+type ULID = string
diff --git a/openmeter/billing/notificationevents/schemas/v1.billing.invoice.created.payload.json b/openmeter/billing/notificationevents/schemas/v1.billing.invoice.created.payload.json
new file mode 100644
index 0000000000..b8574ca923
--- /dev/null
+++ b/openmeter/billing/notificationevents/schemas/v1.billing.invoice.created.payload.json
@@ -0,0 +1,64 @@
+{
+    "$schema": "https://json-schema.org/draft/2020-12/schema",
+    "$id": "v1.billing.invoice.created.payload",
+    "type": "object",
+    "properties": {
+        "invoice_id": {
+            "$ref": "#/$defs/ULID",
+            "description": "Invoice that was created."
+        },
+        "customer_id": {
+            "$ref": "#/$defs/ULID",
+            "description": "Customer the invoice belongs to."
+        },
+        "status": {
+            "type": "string",
+            "description": "Invoice status at creation time."
+        },
+        "currency": {
+            "$ref": "#/$defs/CurrencyCode",
+            "description": "Invoice currency."
+        },
+        "total": {
+            "$ref": "#/$defs/Numeric",
+            "description": "Invoice total at creation time."
+        }
+    },
+    "required": [
+        "invoice_id",
+        "customer_id",
+        "status",
+        "currency",
+        "total"
+    ],
+    "unevaluatedProperties": {
+        "not": {}
+    },
+    "description": "Payload of `v1.billing.invoice.created`.\n\nThe payload identifies the invoice and carries its state at creation time;\nconsumers fetch the full invoice through the API when they need it.",
+    "$defs": {
+        "ULID": {
+            "type": "string",
+            "examples": [
+                "01G65Z755AFWAKHE12NY0CQ9FH"
+            ],
+            "pattern": "^[0-7][0-9A-HJKMNP-TV-Z]{25}$",
+            "description": "ULID (Universally Unique Lexicographically Sortable Identifier).",
+            "title": "ULID"
+        },
+        "CurrencyCode": {
+            "type": "string",
+            "examples": [
+                "USD"
+            ],
+            "minLength": 3,
+            "maxLength": 3,
+            "pattern": "^[A-Z]{3}$",
+            "description": "Three-letter [ISO4217](https://www.iso.org/iso-4217-currency-codes.html)\ncurrency code. Custom three-letter currency codes are also supported for\nconvenience."
+        },
+        "Numeric": {
+            "type": "string",
+            "pattern": "^\\-?[0-9]+(\\.[0-9]+)?$",
+            "description": "Numeric represents an arbitrary precision number."
+        }
+    }
+}
\ No newline at end of file
diff --git a/openmeter/entitlement/notificationevents/events.gen.go b/openmeter/entitlement/notificationevents/events.gen.go
new file mode 100644
index 0000000000..bfc509d384
--- /dev/null
+++ b/openmeter/entitlement/notificationevents/events.gen.go
@@ -0,0 +1,26 @@
+// Code generated by @openmeter/typespec-notification-events, DO NOT EDIT.
+
+package notificationevents
+
+import (
+	_ "embed"
+
+	"github.com/openmeterio/openmeter/openmeter/notification/v4"
+)
+
+// EntitlementBalanceThresholdTriggeredV1EventType is v1.entitlement.balance_threshold.triggered.
+var EntitlementBalanceThresholdTriggeredV1EventType = v4.EventType{
+	Name:    "entitlement.balance_threshold.triggered",
+	Version: 1,
+}
+
+// EntitlementBalanceThresholdTriggeredV1PayloadJSONSchema is the JSON Schema (draft 2020-12) of EntitlementBalanceThresholdTriggeredV1Payload.
+//
+//go:embed schemas/v1.entitlement.balance_threshold.triggered.payload.json
+var EntitlementBalanceThresholdTriggeredV1PayloadJSONSchema []byte
+
+// EntitlementBalanceThresholdTriggeredV1RuleConfigJSONSchema is the JSON Schema (draft 2020-12) of
+// EntitlementBalanceThresholdTriggeredV1RuleConfig, the Rule configuration of v1.entitlement.balance_threshold.triggered.
+//
+//go:embed schemas/v1.entitlement.balance_threshold.triggered.rule_config.json
+var EntitlementBalanceThresholdTriggeredV1RuleConfigJSONSchema []byte
diff --git a/openmeter/entitlement/notificationevents/events_test.go b/openmeter/entitlement/notificationevents/events_test.go
new file mode 100644
index 0000000000..a858f751d0
--- /dev/null
+++ b/openmeter/entitlement/notificationevents/events_test.go
@@ -0,0 +1,96 @@
+package notificationevents
+
+import (
+	"bytes"
+	"encoding/json"
+	"strings"
+	"testing"
+
+	"github.com/santhosh-tekuri/jsonschema/v6"
+	"github.com/stretchr/testify/require"
+)
+
+func compileSchema(t *testing.T, raw []byte) *jsonschema.Schema {
+	t.Helper()
+
+	doc, err := jsonschema.UnmarshalJSON(bytes.NewReader(raw))
+	require.NoError(t, err)
+
+	c := jsonschema.NewCompiler()
+	require.NoError(t, c.AddResource("schema.json", doc))
+
+	s, err := c.Compile("schema.json")
+	require.NoError(t, err)
+
+	return s
+}
+
+func validateJSON(t *testing.T, s *jsonschema.Schema, raw string) error {
+	t.Helper()
+
+	v, err := jsonschema.UnmarshalJSON(strings.NewReader(raw))
+	require.NoError(t, err)
+
+	return s.Validate(v)
+}
+
+func TestBalanceThresholdTriggeredContract(t *testing.T) {
+	require.Equal(t, "v1.entitlement.balance_threshold.triggered", EntitlementBalanceThresholdTriggeredV1EventType.String())
+	require.NoError(t, EntitlementBalanceThresholdTriggeredV1EventType.Validate())
+
+	t.Run("payload struct matches payload schema", func(t *testing.T) {
+		// given the schema generated from the same TypeSpec model as the struct
+		schema := compileSchema(t, EntitlementBalanceThresholdTriggeredV1PayloadJSONSchema)
+
+		// when business logic marshals the generated struct
+		raw, err := json.Marshal(EntitlementBalanceThresholdTriggeredV1Payload{
+			CustomerId:     "01J2KNAG7SY9X6V8E5P4D3C2ZF",
+			EntitlementId:  "01J2KNBH8TZ0Y7W9F6Q5E4D3AG",
+			FeatureKey:     "api_requests",
+			CurrentBalance: 18,
+			Threshold: EntitlementBalanceThreshold{
+				Type:  EntitlementBalanceThresholdTypeBalanceAtOrBelow,
+				Value: 20,
+			},
+		})
+		require.NoError(t, err)
+
+		// then the schema accepts it
+		require.NoError(t, validateJSON(t, schema, string(raw)))
+	})
+
+	t.Run("payload schema rejects unknown properties and enum values", func(t *testing.T) {
+		schema := compileSchema(t, EntitlementBalanceThresholdTriggeredV1PayloadJSONSchema)
+
+		require.Error(t, validateJSON(t, schema, `{
+			"customer_id": "01J2KNAG7SY9X6V8E5P4D3C2ZF",
+			"entitlement_id": "01J2KNBH8TZ0Y7W9F6Q5E4D3AG",
+			"feature_key": "api_requests",
+			"current_balance": 18,
+			"threshold": {"type": "balance_at_or_below", "value": 20},
+			"unexpected": true
+		}`))
+
+		require.Error(t, validateJSON(t, schema, `{
+			"customer_id": "01J2KNAG7SY9X6V8E5P4D3C2ZF",
+			"entitlement_id": "01J2KNBH8TZ0Y7W9F6Q5E4D3AG",
+			"feature_key": "api_requests",
+			"current_balance": 18,
+			"threshold": {"type": "bogus", "value": 20}
+		}`))
+	})
+
+	t.Run("rule config struct matches rule config schema", func(t *testing.T) {
+		schema := compileSchema(t, EntitlementBalanceThresholdTriggeredV1RuleConfigJSONSchema)
+
+		raw, err := json.Marshal(EntitlementBalanceThresholdTriggeredV1RuleConfig{
+			Thresholds: []EntitlementBalanceThreshold{
+				{Type: EntitlementBalanceThresholdTypeUsagePercentageAtOrAbove, Value: 80},
+			},
+		})
+		require.NoError(t, err)
+		require.NoError(t, validateJSON(t, schema, string(raw)))
+
+		require.Error(t, validateJSON(t, schema, `{"thresholds": []}`), "at least one threshold is required")
+	})
+}
diff --git a/openmeter/entitlement/notificationevents/generate.gen.go b/openmeter/entitlement/notificationevents/generate.gen.go
new file mode 100644
index 0000000000..815434b3dc
--- /dev/null
+++ b/openmeter/entitlement/notificationevents/generate.gen.go
@@ -0,0 +1,5 @@
+// Code generated by @openmeter/typespec-notification-events, DO NOT EDIT.
+
+package notificationevents
+
+//go:generate go tool github.com/oapi-codegen/oapi-codegen/v2/cmd/oapi-codegen -config ../../../api/spec/packages/aip/oapi-codegen.notification-events.yaml -package notificationevents -o payloads.gen.go ../../../api/notificationevents/entitlement/openapi.yaml
diff --git a/openmeter/entitlement/notificationevents/notificationevents.go b/openmeter/entitlement/notificationevents/notificationevents.go
new file mode 100644
index 0000000000..b288819da8
--- /dev/null
+++ b/openmeter/entitlement/notificationevents/notificationevents.go
@@ -0,0 +1,5 @@
+// Package notificationevents contains the Notification Event contracts owned
+// by the entitlements domain. Everything else in it is generated from
+// api/spec/packages/aip/src/entitlements/notification-events; run
+// `make gen-api` after changing the TypeSpec.
+package notificationevents
diff --git a/openmeter/entitlement/notificationevents/payloads.gen.go b/openmeter/entitlement/notificationevents/payloads.gen.go
new file mode 100644
index 0000000000..f2f38043ca
--- /dev/null
+++ b/openmeter/entitlement/notificationevents/payloads.gen.go
@@ -0,0 +1,67 @@
+// Package notificationevents provides primitives to interact with the openapi HTTP API.
+//
+// Code generated by github.com/oapi-codegen/oapi-codegen/v2 version v2.7.1 DO NOT EDIT.
+package notificationevents
+
+// Defines values for EntitlementBalanceThresholdType.
+const (
+	EntitlementBalanceThresholdTypeBalanceAtOrBelow         EntitlementBalanceThresholdType = "balance_at_or_below"
+	EntitlementBalanceThresholdTypeUsagePercentageAtOrAbove EntitlementBalanceThresholdType = "usage_percentage_at_or_above"
+)
+
+// Valid indicates whether the value is a known member of the EntitlementBalanceThresholdType enum.
+func (e EntitlementBalanceThresholdType) Valid() bool {
+	switch e {
+	case EntitlementBalanceThresholdTypeBalanceAtOrBelow:
+		return true
+	case EntitlementBalanceThresholdTypeUsagePercentageAtOrAbove:
+		return true
+	default:
+		return false
+	}
+}
+
+// EntitlementBalanceThreshold A single entitlement balance threshold.
+type EntitlementBalanceThreshold struct {
+	// Type Condition kind of the threshold.
+	Type EntitlementBalanceThresholdType `json:"type"`
+
+	// Value Threshold value, interpreted according to the threshold type.
+	Value float64 `json:"value"`
+}
+
+// EntitlementBalanceThresholdTriggeredV1Payload Payload of `v1.entitlement.balance_threshold.triggered`.
+type EntitlementBalanceThresholdTriggeredV1Payload struct {
+	// CurrentBalance Balance at evaluation time.
+	CurrentBalance float64 `json:"current_balance"`
+
+	// CustomerId Customer owning the entitlement.
+	CustomerId ULID `json:"customer_id"`
+
+	// EntitlementId Entitlement whose balance crossed the threshold.
+	EntitlementId ULID `json:"entitlement_id"`
+
+	// FeatureKey Feature of the entitlement.
+	FeatureKey ResourceKey `json:"feature_key"`
+
+	// Threshold Threshold that was crossed.
+	Threshold EntitlementBalanceThreshold `json:"threshold"`
+}
+
+// EntitlementBalanceThresholdTriggeredV1RuleConfig Rule configuration of `v1.entitlement.balance_threshold.triggered`.
+type EntitlementBalanceThresholdTriggeredV1RuleConfig struct {
+	// Features Feature keys the Rule is limited to. All features when omitted.
+	Features *[]ResourceKey `json:"features,omitempty"`
+
+	// Thresholds Thresholds evaluated against the entitlement balance.
+	Thresholds []EntitlementBalanceThreshold `json:"thresholds"`
+}
+
+// EntitlementBalanceThresholdType Condition kind of an entitlement balance threshold.
+type EntitlementBalanceThresholdType string
+
+// ResourceKey A key is a unique string that is used to identify a resource.
+type ResourceKey = string
+
+// ULID ULID (Universally Unique Lexicographically Sortable Identifier).
+type ULID = string
diff --git a/openmeter/entitlement/notificationevents/schemas/v1.entitlement.balance_threshold.triggered.payload.json b/openmeter/entitlement/notificationevents/schemas/v1.entitlement.balance_threshold.triggered.payload.json
new file mode 100644
index 0000000000..5f5b688b37
--- /dev/null
+++ b/openmeter/entitlement/notificationevents/schemas/v1.entitlement.balance_threshold.triggered.payload.json
@@ -0,0 +1,89 @@
+{
+    "$schema": "https://json-schema.org/draft/2020-12/schema",
+    "$id": "v1.entitlement.balance_threshold.triggered.payload",
+    "type": "object",
+    "properties": {
+        "customer_id": {
+            "$ref": "#/$defs/ULID",
+            "description": "Customer owning the entitlement."
+        },
+        "entitlement_id": {
+            "$ref": "#/$defs/ULID",
+            "description": "Entitlement whose balance crossed the threshold."
+        },
+        "feature_key": {
+            "$ref": "#/$defs/ResourceKey",
+            "description": "Feature of the entitlement."
+        },
+        "current_balance": {
+            "type": "number",
+            "description": "Balance at evaluation time."
+        },
+        "threshold": {
+            "$ref": "#/$defs/BalanceThreshold",
+            "description": "Threshold that was crossed."
+        }
+    },
+    "required": [
+        "customer_id",
+        "entitlement_id",
+        "feature_key",
+        "current_balance",
+        "threshold"
+    ],
+    "unevaluatedProperties": {
+        "not": {}
+    },
+    "description": "Payload of `v1.entitlement.balance_threshold.triggered`.",
+    "$defs": {
+        "ULID": {
+            "type": "string",
+            "examples": [
+                "01G65Z755AFWAKHE12NY0CQ9FH"
+            ],
+            "pattern": "^[0-7][0-9A-HJKMNP-TV-Z]{25}$",
+            "description": "ULID (Universally Unique Lexicographically Sortable Identifier).",
+            "title": "ULID"
+        },
+        "ResourceKey": {
+            "type": "string",
+            "examples": [
+                "resource_key"
+            ],
+            "minLength": 1,
+            "maxLength": 64,
+            "pattern": "^[a-z0-9]+(?:_[a-z0-9]+)*$",
+            "description": "A key is a unique string that is used to identify a resource.",
+            "title": "Resource Key"
+        },
+        "BalanceThreshold": {
+            "type": "object",
+            "properties": {
+                "type": {
+                    "$ref": "#/$defs/BalanceThresholdType",
+                    "description": "Condition kind of the threshold."
+                },
+                "value": {
+                    "type": "number",
+                    "description": "Threshold value, interpreted according to the threshold type."
+                }
+            },
+            "required": [
+                "type",
+                "value"
+            ],
+            "unevaluatedProperties": {
+                "not": {}
+            },
+            "description": "A single entitlement balance threshold."
+        },
+        "BalanceThresholdType": {
+            "type": "string",
+            "enum": [
+                "balance_at_or_below",
+                "usage_percentage_at_or_above"
+            ],
+            "description": "Condition kind of an entitlement balance threshold."
+        }
+    }
+}
\ No newline at end of file
diff --git a/openmeter/entitlement/notificationevents/schemas/v1.entitlement.balance_threshold.triggered.rule_config.json b/openmeter/entitlement/notificationevents/schemas/v1.entitlement.balance_threshold.triggered.rule_config.json
new file mode 100644
index 0000000000..d910900669
--- /dev/null
+++ b/openmeter/entitlement/notificationevents/schemas/v1.entitlement.balance_threshold.triggered.rule_config.json
@@ -0,0 +1,71 @@
+{
+    "$schema": "https://json-schema.org/draft/2020-12/schema",
+    "$id": "v1.entitlement.balance_threshold.triggered.rule_config",
+    "type": "object",
+    "properties": {
+        "thresholds": {
+            "type": "array",
+            "items": {
+                "$ref": "#/$defs/BalanceThreshold"
+            },
+            "minItems": 1,
+            "description": "Thresholds evaluated against the entitlement balance."
+        },
+        "features": {
+            "type": "array",
+            "items": {
+                "$ref": "#/$defs/ResourceKey"
+            },
+            "description": "Feature keys the Rule is limited to. All features when omitted."
+        }
+    },
+    "required": [
+        "thresholds"
+    ],
+    "unevaluatedProperties": {
+        "not": {}
+    },
+    "description": "Rule configuration of `v1.entitlement.balance_threshold.triggered`.",
+    "$defs": {
+        "BalanceThreshold": {
+            "type": "object",
+            "properties": {
+                "type": {
+                    "$ref": "#/$defs/BalanceThresholdType",
+                    "description": "Condition kind of the threshold."
+                },
+                "value": {
+                    "type": "number",
+                    "description": "Threshold value, interpreted according to the threshold type."
+                }
+            },
+            "required": [
+                "type",
+                "value"
+            ],
+            "unevaluatedProperties": {
+                "not": {}
+            },
+            "description": "A single entitlement balance threshold."
+        },
+        "ResourceKey": {
+            "type": "string",
+            "examples": [
+                "resource_key"
+            ],
+            "minLength": 1,
+            "maxLength": 64,
+            "pattern": "^[a-z0-9]+(?:_[a-z0-9]+)*$",
+            "description": "A key is a unique string that is used to identify a resource.",
+            "title": "Resource Key"
+        },
+        "BalanceThresholdType": {
+            "type": "string",
+            "enum": [
+                "balance_at_or_below",
+                "usage_percentage_at_or_above"
+            ],
+            "description": "Condition kind of an entitlement balance threshold."
+        }
+    }
+}
\ No newline at end of file
diff --git a/openmeter/notification/v4/event.go b/openmeter/notification/v4/event.go
new file mode 100644
index 0000000000..f47602d98a
--- /dev/null
+++ b/openmeter/notification/v4/event.go
@@ -0,0 +1,47 @@
+// Package v4 holds the Notification vNext types, starting with the identity of
+// Notification Event types. Every domain's generated notificationevents package
+// imports it, so it must not depend on Notification or any domain package.
+package v4
+
+import (
+	"errors"
+	"fmt"
+	"regexp"
+
+	"github.com/openmeterio/openmeter/pkg/models"
+)
+
+// namePattern matches <resource>.<operation> or <subsystem>.<resource>.<operation>
+// with lowercase snake_case segments. Keep it in sync with the @eventType check
+// in api/spec/packages/typespec-notification-events.
+var namePattern = regexp.MustCompile(`^[a-z][a-z0-9_]*(\.[a-z][a-z0-9_]*)+$`)
+
+var _ models.Validator = (*EventType)(nil)
+
+// EventType is a versioned Event type. Its canonical string form,
+// v<version>.<name>, crosses API, Kafka, persistence and Provider boundaries.
+// Versions have no compatibility guarantee: a changed contract is a new
+// version.
+type EventType struct {
+	Name    string
+	Version int
+}
+
+// String returns the canonical form, e.g. v1.billing.invoice.created.
+func (t EventType) String() string {
+	return fmt.Sprintf("v%d.%s", t.Version, t.Name)
+}
+
+func (t EventType) Validate() error {
+	var errs []error
+
+	if !namePattern.MatchString(t.Name) {
+		errs = append(errs, fmt.Errorf("name %q must have at least two lowercase snake_case segments", t.Name))
+	}
+
+	if t.Version < 1 {
+		errs = append(errs, fmt.Errorf("version must be positive, got %d", t.Version))
+	}
+
+	return models.NewNillableGenericValidationError(errors.Join(errs...))
+}
diff --git a/openmeter/notification/v4/event_test.go b/openmeter/notification/v4/event_test.go
new file mode 100644
index 0000000000..3668ce2a90
--- /dev/null
+++ b/openmeter/notification/v4/event_test.go
@@ -0,0 +1,23 @@
+package v4
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestEventType(t *testing.T) {
+	et := EventType{Name: "billing.invoice.created", Version: 1}
+
+	require.Equal(t, "v1.billing.invoice.created", et.String())
+	require.NoError(t, et.Validate())
+
+	for _, invalid := range []EventType{
+		{Name: "invoice", Version: 1},
+		{Name: "Billing.invoice.created", Version: 1},
+		{Name: "billing.invoice.created.", Version: 1},
+		{Name: "billing.invoice.created", Version: 0},
+	} {
+		require.Error(t, invalid.Validate(), invalid.String())
+	}
+}