fix(core): read provider errors from plain AI SDK stream errors (#51194)

packages/ai/src/provider-error.ts

@@ -80,7 +80,13 @@ const SERVER_CODES = new Set([
   "slow_down",
   "serviceunavailableexception",
 ])
-const INVALID_REQUEST_CODES = new Set(["invalid_prompt", "invalid_request_error", "validationexception"])
+// `invalid_request` is the Vercel AI Gateway's code for an upstream request rejection.
+const INVALID_REQUEST_CODES = new Set([
+  "invalid_prompt",
+  "invalid_request",
+  "invalid_request_error",
+  "validationexception",
+])
 // Azure OpenAI reports `content_filter` with `innererror.code` ResponsibleAIPolicyViolation.
 // OpenRouter tags provider failures with a typed `error_type`; its Responses skin also
 // emits `image_content_policy_violation` as the native code.

packages/core/src/aisdk.ts

@@ -24,7 +24,6 @@ import {
   ProviderMetadata,
   TransportError,
   ToolResultValue,
-  UnknownProviderError,
   type ContentPart,
   type LLMRequest,
   type Media,
@@ -936,15 +935,18 @@ function llmError(error: unknown, operation: "request" | "read") {
         code: network.code,
       }),
     })
-  return new AIError({
-    reason: new UnknownProviderError({
-      message: unknownErrorMessage(error),
-      body: errorBody(error),
-      cause: error,
-    }),
+  return RequestExecutor.httpFailure({
+    message: unknownErrorMessage(error),
+    data: errorValue(error) ?? error,
+    responseBody: errorBody(error),
+    cause: error,
   })
 }
 
+// AI SDK stream errors can arrive as plain objects. A gateway's type validation error keeps the provider's error
+// response in `value`, which carries the message and codes.
+const errorValue = (error: unknown) => (ProviderShared.isRecord(error) ? error.value : undefined)
+
 // Runtime-generated network failure shapes. The codes mirror the AI SDK's own
 // Bun network error list in handleFetchError; the messages are undici's fetch
 // TypeError and stream termination strings plus our SSE chunk timeout error.
@@ -1032,7 +1034,15 @@ const decodeProviderError = Schema.decodeUnknownOption(
 )
 
 function unknownErrorMessage(error: unknown) {
-  const message = error instanceof Error ? error.message : String(error)
+  const message =
+    error instanceof Error
+      ? error.message
+      : typeof error === "string"
+        ? error
+        : ([error, errorValue(error)]
+            .map((value) => Option.getOrUndefined(decodeProviderError(value)))
+            .flatMap((decoded) => [decoded?.error?.message, decoded?.message])
+            .find((value) => value?.trim()) ?? "")
   return message.trim() === "" ? "Provider request failed" : message
 }
 

packages/core/test/aisdk.test.ts

@@ -13,6 +13,7 @@ import {
   CompactionPart,
   ProviderID,
   HttpContext,
+  InvalidRequestError,
   LLMEvent,
   Message,
   RateLimitError,
@@ -883,6 +884,23 @@ Object.values({
   )
 })
 
+// Shapes the Vercel AI Gateway streams when the upstream rejects a request.
+Object.entries({
+  "type validation": {
+    name: "AI_TypeValidationError",
+    value: { error: { type: "invalid_request_error", message: "Bad max_tokens" } },
+  },
+  invalid_request: { code: "invalid_request", message: "Bad max_tokens" },
+}).forEach(([shape, failure]) =>
+  it.effect(`reads gateway ${shape} stream errors as invalid requests`, () =>
+    Effect.gen(function* () {
+      const error = yield* streamFailure(failure, true)
+      expect(error.message).toBe("Bad max_tokens")
+      expect(error.reason).toBeInstanceOf(InvalidRequestError)
+    }),
+  ),
+)
+
 it.effect("does not copy Error request internals into the provider body", () =>
   Effect.gen(function* () {
     const cause = Object.assign(new Error("Connection failed"), {