diff --git a/packages/ai/src/protocols/open-responses.ts b/packages/ai/src/protocols/open-responses.ts
index f767fb2e9b7..554997c4333 100644
--- a/packages/ai/src/protocols/open-responses.ts
+++ b/packages/ai/src/protocols/open-responses.ts
@@ -353,6 +353,10 @@ interface ReasoningStreamItem {
   // strings, but typing the map as `Record<number, ...>` documents intent
   // and matches the wire field.
   readonly summaryParts: Readonly<Record<number, ReasoningSummaryStatus>>
+  // Summary indexes that received at least one streamed delta. The `:0` block
+  // is started eagerly when the item opens, so block existence cannot tell
+  // whether a `.done` final would duplicate streamed text.
+  readonly deltaIndexes: ReadonlySet<number>
 }
 
 // =============================================================================
@@ -805,19 +809,33 @@ const onOutputTextDone = (state: ParserState, event: Event, id: string): StepRes
 }
 
 export const onReasoningDelta = (state: ParserState, event: Event, itemID: string): StepResult => {
-  if (!event.delta || !state.reasoningItems[itemID]) return [state, NO_EVENTS]
+  const item = state.reasoningItems[itemID]
+  if (!event.delta || !item) return [state, NO_EVENTS]
+  const index = event.summary_index ?? 0
   const events: LLMEvent[] = []
-  const id = `${itemID}:${event.summary_index ?? 0}`
   return [
     {
       ...state,
-      lifecycle: Lifecycle.reasoningDelta(state.lifecycle, events, id, event.delta),
+      lifecycle: Lifecycle.reasoningDelta(state.lifecycle, events, `${itemID}:${index}`, event.delta),
+      reasoningItems: {
+        ...state.reasoningItems,
+        [itemID]: { ...item, deltaIndexes: new Set([...item.deltaIndexes, index]) },
+      },
     },
     events,
   ]
 }
 
-export const onReasoningDone = (state: ParserState, _event: Event): StepResult => [state, NO_EVENTS]
+// Some compatible gateways emit a reasoning final without streaming any
+// deltas, mirroring `response.output_text.done`. Reconcile the complete text
+// as a single delta unless that summary index already streamed one.
+export const onReasoningDone = (state: ParserState, event: Event, itemID: string): StepResult => {
+  const item = state.reasoningItems[itemID]
+  if (!item || typeof event.text !== "string") return [state, NO_EVENTS]
+  const index = event.summary_index ?? 0
+  if (item.deltaIndexes.has(index)) return [state, NO_EVENTS]
+  return onReasoningDelta(state, { ...event, delta: event.text }, itemID)
+}
 
 const reasoningMetadata = (state: ParserState, item: StreamItem & { id: string }) =>
   providerMetadata(state, { itemId: item.id, reasoningEncryptedContent: item.encrypted_content ?? null })
@@ -855,7 +873,11 @@ const onOutputItemAdded = (state: ParserState, event: Event): StepResult => {
         lifecycle: Lifecycle.reasoningStart(state.lifecycle, events, `${item.id}:0`, reasoningMetadata(state, item)),
         reasoningItems: {
           ...state.reasoningItems,
-          [item.id]: { encryptedContent: item.encrypted_content, summaryParts: { 0: "active" } },
+          [item.id]: {
+            encryptedContent: item.encrypted_content,
+            summaryParts: { 0: "active" },
+            deltaIndexes: new Set(),
+          },
         },
       },
       events,
@@ -1161,6 +1183,15 @@ export const step = (state: ParserState, event: Event) => {
     if (!event.item_id) return ProviderShared.eventError(state.id, `${event.type} is missing item_id`)
     return Effect.succeed(onReasoningDelta(state, event, event.item_id))
   }
+  if (
+    event.type === "response.reasoning.done" ||
+    event.type === "response.reasoning_summary_text.done" ||
+    event.type === "response.reasoning_summary.done" ||
+    event.type === "response.reasoning_text.done"
+  ) {
+    if (!event.item_id) return ProviderShared.eventError(state.id, `${event.type} is missing item_id`)
+    return Effect.succeed(onReasoningDone(state, event, event.item_id))
+  }
   if (event.type === "response.reasoning_summary_part.added")
     return event.item_id
       ? Effect.succeed(onReasoningSummaryPartAdded(state, event))
diff --git a/packages/ai/src/protocols/openai-responses.ts b/packages/ai/src/protocols/openai-responses.ts
index ae2c8ca89c8..e93e6feafc0 100644
--- a/packages/ai/src/protocols/openai-responses.ts
+++ b/packages/ai/src/protocols/openai-responses.ts
@@ -166,10 +166,6 @@ const step = (state: OpenResponses.ParserState, event: OpenResponses.Event) => {
     return event.item_id
       ? Effect.succeed(OpenResponses.onReasoningDelta(state, event, event.item_id))
       : ProviderShared.eventError(ADAPTER, `${event.type} is missing item_id`)
-  if (event.type === "response.reasoning_text.done" || event.type === "response.reasoning_summary.done")
-    return event.item_id
-      ? Effect.succeed(OpenResponses.onReasoningDone(state, event))
-      : ProviderShared.eventError(ADAPTER, `${event.type} is missing item_id`)
   if (event.type === "response.output_item.done" && event.item && ResponsesHostedTools.isItem(event.item, HOSTED_TOOLS))
     return ResponsesHostedTools.onDone(state, event.item, HOSTED_TOOLS)
   return OpenResponses.step(state, event)
diff --git a/packages/ai/src/protocols/xai-responses.ts b/packages/ai/src/protocols/xai-responses.ts
index 01ab748946a..9a620927c24 100644
--- a/packages/ai/src/protocols/xai-responses.ts
+++ b/packages/ai/src/protocols/xai-responses.ts
@@ -1,7 +1,5 @@
-import { Effect } from "effect"
 import { Protocol } from "../route/protocol.js"
 import { OpenResponses } from "./open-responses.js"
-import { ProviderShared } from "./shared.js"
 import { ResponsesHostedTools } from "./utils/responses-hosted-tools.js"
 
 const ADAPTER = "xai-responses"
@@ -27,15 +25,9 @@ const HOSTED_TOOLS = {
   },
 } as const satisfies ResponsesHostedTools.Definitions
 
+// Grok speaks the standard Responses reasoning dialect (`reasoning_summary_text.*`,
+// handled by the baseline); only its hosted tool vocabulary differs.
 const step = (state: OpenResponses.ParserState, event: OpenResponses.Event) => {
-  if (event.type === "response.reasoning_text.delta" || event.type === "response.reasoning_summary.delta")
-    return event.item_id
-      ? Effect.succeed(OpenResponses.onReasoningDelta(state, event, event.item_id))
-      : ProviderShared.eventError(ADAPTER, `${event.type} is missing item_id`)
-  if (event.type === "response.reasoning_text.done" || event.type === "response.reasoning_summary.done")
-    return event.item_id
-      ? Effect.succeed(OpenResponses.onReasoningDone(state, event))
-      : ProviderShared.eventError(ADAPTER, `${event.type} is missing item_id`)
   if (event.type === "response.output_item.done" && event.item && ResponsesHostedTools.isItem(event.item, HOSTED_TOOLS))
     return ResponsesHostedTools.onDone(state, event.item, HOSTED_TOOLS)
   return OpenResponses.step(state, event)
diff --git a/packages/ai/test/provider/openai-compatible-responses.test.ts b/packages/ai/test/provider/openai-compatible-responses.test.ts
index 859312c4f6d..22c5f8f5d31 100644
--- a/packages/ai/test/provider/openai-compatible-responses.test.ts
+++ b/packages/ai/test/provider/openai-compatible-responses.test.ts
@@ -173,6 +173,37 @@ describe("Open Responses-compatible route", () => {
     }),
   )
 
+  it.effect("reconciles raw reasoning finals without streamed deltas", () =>
+    Effect.gen(function* () {
+      const model = configure({
+        apiKey: "test-key",
+        baseURL: "https://responses.example.test/v1",
+      }).model("example-model")
+      const response = yield* LLMClient.generate(LLM.request({ model, prompt: "Think it through." })).pipe(
+        Effect.provide(
+          fixedResponse(
+            sseEvents(
+              {
+                type: "response.output_item.added",
+                item: { type: "reasoning", id: "rs_raw", encrypted_content: null },
+              },
+              // Raw reasoning finals carry no summary index; they reconcile
+              // into the item's first block.
+              { type: "response.reasoning.done", item_id: "rs_raw", text: "Raw chain of thought." },
+              {
+                type: "response.output_item.done",
+                item: { type: "reasoning", id: "rs_raw", encrypted_content: "raw-state" },
+              },
+              { type: "response.completed", response: { id: "resp_1" } },
+            ),
+          ),
+        ),
+      )
+
+      expect(response.reasoning).toBe("Raw chain of thought.")
+    }),
+  )
+
   it.effect("preserves nullable phases in the forgiving Open Responses baseline", () =>
     Effect.gen(function* () {
       const model = configure({
diff --git a/packages/ai/test/provider/openai-responses.test.ts b/packages/ai/test/provider/openai-responses.test.ts
index 3587efc1f6b..9fd367a684f 100644
--- a/packages/ai/test/provider/openai-responses.test.ts
+++ b/packages/ai/test/provider/openai-responses.test.ts
@@ -2196,6 +2196,105 @@ describe("OpenAI Responses route", () => {
     }),
   )
 
+  it.effect("reconciles reasoning summaries that arrive only as finals", () =>
+    Effect.gen(function* () {
+      const response = yield* LLMClient.generate(
+        LLMRequest.update(request, { providerOptions: { store: false } }),
+      ).pipe(
+        Effect.provide(
+          fixedResponse(
+            sseEvents(
+              {
+                type: "response.output_item.added",
+                item: { type: "reasoning", id: "rs_1", encrypted_content: null },
+              },
+              { type: "response.reasoning_summary_part.added", item_id: "rs_1", summary_index: 0 },
+              // No `.delta` events at all: the gateway sends the complete
+              // summary text in the `.done` final.
+              {
+                type: "response.reasoning_summary_text.done",
+                item_id: "rs_1",
+                summary_index: 0,
+                text: "Checked the diff.",
+              },
+              { type: "response.reasoning_summary_part.done", item_id: "rs_1", summary_index: 0 },
+              {
+                type: "response.output_item.done",
+                item: {
+                  type: "reasoning",
+                  id: "rs_1",
+                  summary: [{ type: "summary_text", text: "Checked the diff." }],
+                  encrypted_content: "encrypted-state",
+                },
+              },
+              { type: "response.completed", response: { id: "resp_1" } },
+            ),
+          ),
+        ),
+      )
+
+      expect(response.reasoning).toBe("Checked the diff.")
+      expect(response.events.filter((event) => event.type.startsWith("reasoning-"))).toEqual([
+        {
+          type: "reasoning-start",
+          id: "rs_1:0",
+          providerMetadata: { openai: { itemId: "rs_1", reasoningEncryptedContent: null } },
+        },
+        { type: "reasoning-delta", id: "rs_1:0", text: "Checked the diff.", providerMetadata: undefined },
+        {
+          type: "reasoning-end",
+          id: "rs_1:0",
+          providerMetadata: { openai: { itemId: "rs_1", reasoningEncryptedContent: "encrypted-state" } },
+        },
+      ])
+
+      const prepared = yield* compileRequest(
+        LLM.request({
+          model,
+          messages: [response.message],
+          providerOptions: { store: false, include: ["reasoning.encrypted_content"] },
+        }),
+      )
+      expect(prepared.body.input).toEqual([
+        {
+          type: "reasoning",
+          id: "rs_1",
+          summary: [{ type: "summary_text", text: "Checked the diff." }],
+          encrypted_content: "encrypted-state",
+        },
+      ])
+    }),
+  )
+
+  it.effect("does not duplicate reasoning finals after streamed deltas", () =>
+    Effect.gen(function* () {
+      const response = yield* LLMClient.generate(request).pipe(
+        Effect.provide(
+          fixedResponse(
+            sseEvents(
+              { type: "response.output_item.added", item: { type: "reasoning", id: "rs_1", encrypted_content: null } },
+              { type: "response.reasoning_summary_part.added", item_id: "rs_1", summary_index: 0 },
+              { type: "response.reasoning_summary_text.delta", item_id: "rs_1", summary_index: 0, delta: "Streamed" },
+              // Repeats the complete text, as the spec allows.
+              { type: "response.reasoning_summary_text.done", item_id: "rs_1", summary_index: 0, text: "Streamed" },
+              { type: "response.reasoning_summary_part.done", item_id: "rs_1", summary_index: 0 },
+              {
+                type: "response.output_item.done",
+                item: { type: "reasoning", id: "rs_1", encrypted_content: "encrypted-state" },
+              },
+              { type: "response.completed", response: { id: "resp_1" } },
+            ),
+          ),
+        ),
+      )
+
+      expect(response.reasoning).toBe("Streamed")
+      expect(response.events.filter((event) => event.type === "reasoning-delta")).toEqual([
+        { type: "reasoning-delta", id: "rs_1:0", text: "Streamed", providerMetadata: undefined },
+      ])
+    }),
+  )
+
   it.effect("closes reasoning summary parts when storage is not disabled", () =>
     Effect.gen(function* () {
       const response = yield* LLMClient.generate(LLMRequest.update(request, { providerOptions: { store: true } })).pipe(
diff --git a/packages/ai/test/provider/xai-responses.test.ts b/packages/ai/test/provider/xai-responses.test.ts
index 5defc903623..211cace89eb 100644
--- a/packages/ai/test/provider/xai-responses.test.ts
+++ b/packages/ai/test/provider/xai-responses.test.ts
@@ -24,7 +24,7 @@ describe("xAI Responses route", () => {
     }),
   )
 
-  it.effect("parses xAI reasoning text events", () =>
+  it.effect("parses xAI reasoning summaries", () =>
     Effect.gen(function* () {
       const response = yield* LLMClient.generate(LLM.request({ model, prompt: "Think" })).pipe(
         Effect.provide(
@@ -34,8 +34,13 @@ describe("xAI Responses route", () => {
                 type: "response.output_item.added",
                 item: { type: "reasoning", id: "reasoning_1" },
               },
-              { type: "response.reasoning_text.delta", item_id: "reasoning_1", delta: "Considering." },
-              { type: "response.reasoning_text.done", item_id: "reasoning_1" },
+              // Grok streams reasoning with the standard summary event name.
+              {
+                type: "response.reasoning_summary_text.delta",
+                item_id: "reasoning_1",
+                summary_index: 0,
+                delta: "Considering.",
+              },
               {
                 type: "response.output_item.done",
                 item: { type: "reasoning", id: "reasoning_1", encrypted_content: "opaque" },