feat(ai): add Vercel AI Gateway routing support (#1051)

* feat(ai): add Vercel AI Gateway routing support

Add vercelGatewayRouting to OpenAICompletionsCompat, parallel to
openRouterRouting. When a model targets ai-gateway.vercel.sh and has
vercelGatewayRouting configured, the openai-completions provider passes
providerOptions.gateway with only/order in the request body.

Changes:
- types.ts: VercelGatewayRouting interface + field on OpenAICompletionsCompat
- openai-completions.ts: buildParams passes providerOptions.gateway,
  detectCompat/getCompat include the new field
- model-registry.ts: VercelGatewayRoutingSchema for models.json validation
- test: updated Required<OpenAICompletionsCompat> in test fixture

* docs(coding-agent): add vercelGatewayRouting to custom models documentation

packages/ai/src/providers/openai-completions.ts

@@ -452,6 +452,17 @@ function buildParams(model: Model<"openai-completions">, context: Context, optio
 		(params as any).provider = model.compat.openRouterRouting;
 	}
 
+	// Vercel AI Gateway provider routing preferences
+	if (model.baseUrl.includes("ai-gateway.vercel.sh") && model.compat?.vercelGatewayRouting) {
+		const routing = model.compat.vercelGatewayRouting;
+		if (routing.only || routing.order) {
+			const gatewayOptions: Record<string, string[]> = {};
+			if (routing.only) gatewayOptions.only = routing.only;
+			if (routing.order) gatewayOptions.order = routing.order;
+			(params as any).providerOptions = { gateway: gatewayOptions };
+		}
+	}
+
 	return params;
 }
 
@@ -797,6 +808,7 @@ function detectCompat(model: Model<"openai-completions">): Required<OpenAIComple
 		requiresMistralToolIds: isMistral,
 		thinkingFormat: isZai ? "zai" : "openai",
 		openRouterRouting: {},
+		vercelGatewayRouting: {},
 	};
 }
 
@@ -821,5 +833,6 @@ function getCompat(model: Model<"openai-completions">): Required<OpenAICompletio
 		requiresMistralToolIds: model.compat.requiresMistralToolIds ?? detected.requiresMistralToolIds,
 		thinkingFormat: model.compat.thinkingFormat ?? detected.thinkingFormat,
 		openRouterRouting: model.compat.openRouterRouting ?? {},
+		vercelGatewayRouting: model.compat.vercelGatewayRouting ?? detected.vercelGatewayRouting,
 	};
 }

packages/ai/src/types.ts

@@ -218,6 +218,8 @@ export interface OpenAICompletionsCompat {
 	thinkingFormat?: "openai" | "zai";
 	/** OpenRouter-specific routing preferences. Only used when baseUrl points to OpenRouter. */
 	openRouterRouting?: OpenRouterRouting;
+	/** Vercel AI Gateway routing preferences. Only used when baseUrl points to Vercel AI Gateway. */
+	vercelGatewayRouting?: VercelGatewayRouting;
 }
 
 /** Compatibility settings for OpenAI Responses APIs. */
@@ -237,6 +239,18 @@ export interface OpenRouterRouting {
 	order?: string[];
 }
 
+/**
+ * Vercel AI Gateway routing preferences.
+ * Controls which upstream providers the gateway routes requests to.
+ * @see https://vercel.com/docs/ai-gateway/models-and-providers/provider-options
+ */
+export interface VercelGatewayRouting {
+	/** List of provider slugs to exclusively use for this request (e.g., ["bedrock", "anthropic"]). */
+	only?: string[];
+	/** List of provider slugs to try in order (e.g., ["anthropic", "openai"]). */
+	order?: string[];
+}
+
 // Model interface for the unified model system
 export interface Model<TApi extends Api> {
 	id: string;

packages/ai/test/openai-completions-tool-result-images.test.ts

@@ -31,6 +31,7 @@ const compat: Required<OpenAICompletionsCompat> = {
 	requiresMistralToolIds: false,
 	thinkingFormat: "openai",
 	openRouterRouting: {},
+	vercelGatewayRouting: {},
 };
 
 function buildToolResult(toolCallId: string, timestamp: number): ToolResultMessage {