fix: improve xai cache hit rate (#35970)

packages/core/package.json

@@ -80,7 +80,7 @@
     "@ai-sdk/provider-utils": "4.0.23",
     "@ai-sdk/togetherai": "2.0.41",
     "@ai-sdk/vercel": "2.0.39",
-    "@ai-sdk/xai": "3.0.82",
+    "@ai-sdk/xai": "3.0.102",
     "@aws-sdk/credential-providers": "3.1057.0",
     "@effect/opentelemetry": "catalog:",
     "@effect/platform-node": "catalog:",

packages/core/test/provider-xai-responses.test.ts

@@ -0,0 +1,32 @@
+import { createXai } from "@ai-sdk/xai"
+import { expect, test } from "bun:test"
+
+test("xAI Responses sends promptCacheKey as prompt_cache_key", async () => {
+  let body: Record<string, unknown> | undefined
+  const mockFetch = Object.assign(
+    async (_input: Parameters<typeof fetch>[0], init?: RequestInit) => {
+      body = JSON.parse(String(init?.body))
+      return Response.json({
+        id: "response-1",
+        created_at: 0,
+        model: "grok-4",
+        object: "response",
+        output: [],
+        usage: { input_tokens: 1, output_tokens: 0 },
+        status: "completed",
+      })
+    },
+    { preconnect: fetch.preconnect },
+  )
+  const model = createXai({
+    apiKey: "test",
+    fetch: mockFetch,
+  }).responses("grok-4")
+
+  await model.doGenerate({
+    prompt: [{ role: "user", content: [{ type: "text", text: "Hello" }] }],
+    providerOptions: { xai: { promptCacheKey: "session-123" } },
+  })
+
+  expect(body?.prompt_cache_key).toBe("session-123")
+})