diff --git a/apps/cli/ai/providers.ts b/apps/cli/ai/providers.ts
index 8be5cf620d..746d8f6dac 100644
--- a/apps/cli/ai/providers.ts
+++ b/apps/cli/ai/providers.ts
@@ -1,4 +1,5 @@
 import { password } from '@inquirer/prompts';
+import { validateAnthropicApiKey } from '@studio/common/ai/anthropic-key';
 import {
 	AI_MODELS,
 	DEFAULT_MODEL,
@@ -78,22 +79,30 @@ async function resolveAnthropicApiKey( options?: {
 } ): Promise< string | undefined > {
 	const { anthropicApiKey: savedKey } = await readCliConfig();
 	if ( savedKey && ! options?.force ) {
-		return savedKey;
+		// Re-prompt only when Anthropic definitively rejects the saved key;
+		// an unreachable API must not lock the user out of their provider.
+		const validation = await validateAnthropicApiKey( savedKey );
+		if ( validation.status !== 'invalid' ) {
+			return savedKey;
+		}
 	}
 
 	const apiKey = await password( {
 		message: __( 'Enter your Anthropic API key (will be saved for future use):' ),
 		mask: '*',
-		validate: ( value ) => {
-			if ( ! value.trim() ) {
+		validate: async ( value ) => {
+			const trimmed = value.trim();
+			if ( ! trimmed ) {
 				return __( 'API key is required' );
 			}
-			return true;
+			const validation = await validateAnthropicApiKey( trimmed );
+			return validation.status === 'invalid' ? validation.message : true;
 		},
 	} );
 
-	await updateCliConfigWithPartial( { anthropicApiKey: apiKey } );
-	return apiKey;
+	const trimmedKey = apiKey.trim();
+	await updateCliConfigWithPartial( { anthropicApiKey: trimmedKey } );
+	return trimmedKey;
 }
 
 function getStudioUserAgent(): string {
diff --git a/packages/common/ai/anthropic-key.ts b/packages/common/ai/anthropic-key.ts
new file mode 100644
index 0000000000..edad8dff74
--- /dev/null
+++ b/packages/common/ai/anthropic-key.ts
@@ -0,0 +1,51 @@
+import { __ } from '@wordpress/i18n';
+
+const ANTHROPIC_MODELS_URL = 'https://api.anthropic.com/v1/models?limit=1';
+const ANTHROPIC_API_VERSION = '2023-06-01';
+const VALIDATION_TIMEOUT_MS = 10_000;
+
+export type AnthropicKeyValidation =
+	| { status: 'valid' }
+	| { status: 'invalid'; message: string }
+	| { status: 'unverifiable'; message: string };
+
+/**
+ * Checks an Anthropic API key against the live API with a cheap authenticated
+ * request (listing models consumes no tokens).
+ *
+ * Only a definitive authentication failure reports `invalid`; rate limits,
+ * server errors, and network failures report `unverifiable` so callers can
+ * decide whether to accept the key anyway (e.g. saving while offline) rather
+ * than locking the user out on an Anthropic outage.
+ */
+export async function validateAnthropicApiKey( apiKey: string ): Promise< AnthropicKeyValidation > {
+	let response: Response;
+	try {
+		response = await fetch( ANTHROPIC_MODELS_URL, {
+			headers: {
+				'x-api-key': apiKey,
+				'anthropic-version': ANTHROPIC_API_VERSION,
+			},
+			signal: AbortSignal.timeout( VALIDATION_TIMEOUT_MS ),
+		} );
+	} catch {
+		return {
+			status: 'unverifiable',
+			message: __( 'Could not reach Anthropic to verify the API key.' ),
+		};
+	}
+
+	if ( response.ok ) {
+		return { status: 'valid' };
+	}
+	if ( response.status === 401 || response.status === 403 ) {
+		return {
+			status: 'invalid',
+			message: __( 'Anthropic rejected this API key. Check the key and try again.' ),
+		};
+	}
+	return {
+		status: 'unverifiable',
+		message: __( 'Could not verify the API key with Anthropic.' ),
+	};
+}
diff --git a/packages/common/ai/tests/anthropic-key.test.ts b/packages/common/ai/tests/anthropic-key.test.ts
new file mode 100644
index 0000000000..735fea8726
--- /dev/null
+++ b/packages/common/ai/tests/anthropic-key.test.ts
@@ -0,0 +1,61 @@
+import { afterEach, describe, expect, it, vi } from 'vitest';
+import { validateAnthropicApiKey } from '../anthropic-key';
+
+describe( 'validateAnthropicApiKey', () => {
+	afterEach( () => {
+		vi.unstubAllGlobals();
+	} );
+
+	function stubFetch( response: Partial< Response > | Error ) {
+		const fetchMock =
+			response instanceof Error
+				? vi.fn().mockRejectedValue( response )
+				: vi.fn().mockResolvedValue( response );
+		vi.stubGlobal( 'fetch', fetchMock );
+		return fetchMock;
+	}
+
+	it( 'reports a working key as valid and sends the Anthropic auth headers', async () => {
+		const fetchMock = stubFetch( { ok: true, status: 200 } );
+
+		await expect( validateAnthropicApiKey( 'sk-ant-test-1234' ) ).resolves.toEqual( {
+			status: 'valid',
+		} );
+		expect( fetchMock ).toHaveBeenCalledWith(
+			'https://api.anthropic.com/v1/models?limit=1',
+			expect.objectContaining( {
+				headers: expect.objectContaining( { 'x-api-key': 'sk-ant-test-1234' } ),
+			} )
+		);
+	} );
+
+	it.each( [ 401, 403 ] )(
+		'reports an authentication failure (%d) as invalid',
+		async ( status ) => {
+			stubFetch( { ok: false, status } );
+
+			await expect( validateAnthropicApiKey( 'sk-ant-bad' ) ).resolves.toMatchObject( {
+				status: 'invalid',
+			} );
+		}
+	);
+
+	it.each( [ 429, 500 ] )(
+		'reports a non-auth API failure (%d) as unverifiable, not invalid',
+		async ( status ) => {
+			stubFetch( { ok: false, status } );
+
+			await expect( validateAnthropicApiKey( 'sk-ant-test-1234' ) ).resolves.toMatchObject( {
+				status: 'unverifiable',
+			} );
+		}
+	);
+
+	it( 'reports a network failure as unverifiable', async () => {
+		stubFetch( new Error( 'network down' ) );
+
+		await expect( validateAnthropicApiKey( 'sk-ant-test-1234' ) ).resolves.toMatchObject( {
+			status: 'unverifiable',
+		} );
+	} );
+} );