diff --git a/packages/fold-agent/src/Config/ModelSelections.ts b/packages/fold-agent/src/Config/ModelSelections.ts
index f3067c0..3df12c8 100644
--- a/packages/fold-agent/src/Config/ModelSelections.ts
+++ b/packages/fold-agent/src/Config/ModelSelections.ts
@@ -1,8 +1,8 @@
 import { DEFAULT_CODEX_MODEL_ID } from '@humanlayer/fold-codex'
 import { DEFAULT_ANTHROPIC_MODEL_ID, type ModelCatalogEntry, type FoldModel } from '@humanlayer/fold-core'
 import { DEFAULT_OPENCODE_MODEL_ID, GROK_BUILD_MODEL_ID } from '@humanlayer/fold-opencode'
-import { DEFAULT_XAI_MODEL_ID } from '@humanlayer/fold-xai'
-import { Predicate, Effect, Match } from 'effect'
+import { DEFAULT_XAI_MODEL_ID, XAI_FRONTIER_MODELS } from '@humanlayer/fold-xai'
+import { Effect, Match, Predicate } from 'effect'
 
 import { agentModelsFromConfig, type AgentModelsOptions, RoleResolutionError } from './AgentModels'
 import type { ConfigRole, ProfileConfig, ProfileModeName, RoleBinding, FoldConfig } from './ConfigSchema'
@@ -77,7 +77,7 @@ export const describeModelConfiguration = (
 		const defaultModels = Match.value(provider.kind).pipe(
 			Match.when('codex', () => [DEFAULT_OPENCODE_MODEL_ID]),
 			Match.when('opencode', () => [DEFAULT_OPENCODE_MODEL_ID, GROK_BUILD_MODEL_ID]),
-			Match.when('xai', () => ['grok-4.5', DEFAULT_XAI_MODEL_ID]),
+			Match.when('xai', () => XAI_FRONTIER_MODELS.map(({ modelId }) => modelId)),
 			Match.orElse((): ReadonlyArray<string> => []),
 		)
 		const models = [
diff --git a/packages/fold-xai/src/XaiModel.ts b/packages/fold-xai/src/XaiModel.ts
index 3465ac5..931a223 100644
--- a/packages/fold-xai/src/XaiModel.ts
+++ b/packages/fold-xai/src/XaiModel.ts
@@ -10,9 +10,9 @@ import { FetchHttpClient, HttpClient } from 'effect/unstable/http'
 
 import type { XaiAuthStore } from './AuthStore'
 import { makeXaiAuth, withXaiAuth } from './XaiAuth'
+import { DEFAULT_XAI_MODEL_ID } from './XaiModelCatalog'
 
 export const XAI_API_URL = 'https://api.x.ai/v1'
-export const DEFAULT_XAI_MODEL_ID = 'grok-4.6'
 
 export type XaiModelOptions = {
 	readonly model?: string
diff --git a/packages/fold-xai/src/XaiModelCatalog.ts b/packages/fold-xai/src/XaiModelCatalog.ts
new file mode 100644
index 0000000..fe017b8
--- /dev/null
+++ b/packages/fold-xai/src/XaiModelCatalog.ts
@@ -0,0 +1,21 @@
+import { Schema } from 'effect'
+
+/** Model IDs verified for xAI subscription-backed OAuth sessions. */
+export const XaiFrontierModelId = Schema.Literals(['grok-4.5', 'grok-4.6'])
+export type XaiFrontierModelId = typeof XaiFrontierModelId.Type
+
+/** One model exposed to embedding hosts for validation and selection controls. */
+export const XaiFrontierModel = Schema.Struct({
+	modelId: XaiFrontierModelId,
+	label: Schema.NonEmptyString,
+})
+export type XaiFrontierModel = typeof XaiFrontierModel.Type
+
+/** Frontier Grok models supported by Fold's xAI OAuth transport. */
+export const XAI_FRONTIER_MODELS = [
+	{ modelId: 'grok-4.5', label: 'Grok 4.5' },
+	{ modelId: 'grok-4.6', label: 'Grok 4.6' },
+] as const satisfies ReadonlyArray<XaiFrontierModel>
+
+/** The model selected when an embedding host does not provide one. */
+export const DEFAULT_XAI_MODEL_ID: XaiFrontierModelId = 'grok-4.6'
diff --git a/packages/fold-xai/src/index.ts b/packages/fold-xai/src/index.ts
index 413bc30..45ecb09 100644
--- a/packages/fold-xai/src/index.ts
+++ b/packages/fold-xai/src/index.ts
@@ -2,3 +2,4 @@ export * from './AuthStore'
 export * from './OAuthFlows'
 export * from './XaiAuth'
 export * from './XaiModel'
+export * from './XaiModelCatalog'
diff --git a/packages/fold-xai/test/Xai.vi.test.ts b/packages/fold-xai/test/Xai.vi.test.ts
index d26c954..f86359b 100644
--- a/packages/fold-xai/test/Xai.vi.test.ts
+++ b/packages/fold-xai/test/Xai.vi.test.ts
@@ -2,15 +2,17 @@ import { readdir, rm } from 'node:fs/promises'
 
 import * as NodeFileSystem from '@effect/platform-node/NodeFileSystem'
 import { describe, expect, it } from '@effect/vitest'
-import { Effect, Option } from 'effect'
+import { Effect, Option, Schema } from 'effect'
 
 import {
 	buildXaiAuthorizeUrl,
 	DEFAULT_XAI_MODEL_ID,
 	makeXaiAuthStore,
+	XAI_FRONTIER_MODELS,
 	XAI_BROWSER_REDIRECT_URI,
 	XAI_CLIENT_ID,
 	xaiModel,
+	XaiFrontierModelId,
 	XaiTokenData,
 } from '../src/index'
 
@@ -48,6 +50,17 @@ describe('xAI OAuth', () => {
 })
 
 describe('xaiModel', () => {
+	it('exports the supported frontier catalog and defaults to its newest model', () => {
+		expect(XAI_FRONTIER_MODELS).toEqual([
+			{ modelId: 'grok-4.5', label: 'Grok 4.5' },
+			{ modelId: 'grok-4.6', label: 'Grok 4.6' },
+		])
+		expect(XAI_FRONTIER_MODELS.at(-1)?.modelId).toBe(DEFAULT_XAI_MODEL_ID)
+		expect(Schema.is(XaiFrontierModelId)('grok-4.5')).toBe(true)
+		expect(Schema.is(XaiFrontierModelId)('grok-4.6')).toBe(true)
+		expect(Schema.is(XaiFrontierModelId)('grok-unverified')).toBe(false)
+	})
+
 	it('returns a FoldModel-compatible OpenAI snapshot', () => {
 		const model = xaiModel()
 		expect(model.activeModel).toMatchObject({