diff --git a/src/agents/pi-embedded-runner/moonshot-stream-wrappers.ts b/src/agents/pi-embedded-runner/moonshot-stream-wrappers.ts
index c066a168a0f..f9ce52eb234 100644
--- a/src/agents/pi-embedded-runner/moonshot-stream-wrappers.ts
+++ b/src/agents/pi-embedded-runner/moonshot-stream-wrappers.ts
@@ -1,6 +1,7 @@
 import type { StreamFn } from "@mariozechner/pi-agent-core";
 import { streamSimple } from "@mariozechner/pi-ai";
 import type { ThinkLevel } from "../../auto-reply/thinking.js";
+import { usesMoonshotThinkingPayloadCompat } from "../provider-capabilities.js";
 
 type MoonshotThinkingType = "enabled" | "disabled";
 
@@ -62,7 +63,7 @@ export function shouldApplyMoonshotPayloadCompat(params: {
   const normalizedProvider = params.provider.trim().toLowerCase();
   const normalizedModelId = params.modelId.trim().toLowerCase();
 
-  if (normalizedProvider === "moonshot") {
+  if (usesMoonshotThinkingPayloadCompat(normalizedProvider)) {
     return true;
   }
 
diff --git a/src/agents/pi-embedded-runner/xai-stream-wrappers.test.ts b/src/agents/pi-embedded-runner/xai-stream-wrappers.test.ts
new file mode 100644
index 00000000000..a005f2c4721
--- /dev/null
+++ b/src/agents/pi-embedded-runner/xai-stream-wrappers.test.ts
@@ -0,0 +1,39 @@
+import type { StreamFn } from "@mariozechner/pi-agent-core";
+import type { Context, Model } from "@mariozechner/pi-ai";
+import { describe, expect, it } from "vitest";
+import { createXaiFastModeWrapper } from "./xai-stream-wrappers.js";
+
+function captureWrappedModelId(params: { modelId: string; fastMode: boolean }): string {
+  let capturedModelId = "";
+  const baseStreamFn: StreamFn = (model) => {
+    capturedModelId = model.id;
+    return {} as ReturnType<StreamFn>;
+  };
+
+  const wrapped = createXaiFastModeWrapper(baseStreamFn, params.fastMode);
+  void wrapped(
+    {
+      api: "openai-completions",
+      provider: "xai",
+      id: params.modelId,
+    } as Model<"openai-completions">,
+    { messages: [] } as Context,
+    {},
+  );
+
+  return capturedModelId;
+}
+
+describe("xai fast mode wrapper", () => {
+  it("rewrites Grok 3 models to fast variants", () => {
+    expect(captureWrappedModelId({ modelId: "grok-3", fastMode: true })).toBe("grok-3-fast");
+    expect(captureWrappedModelId({ modelId: "grok-3-mini", fastMode: true })).toBe(
+      "grok-3-mini-fast",
+    );
+  });
+
+  it("leaves unsupported or disabled models unchanged", () => {
+    expect(captureWrappedModelId({ modelId: "grok-3-fast", fastMode: true })).toBe("grok-3-fast");
+    expect(captureWrappedModelId({ modelId: "grok-3", fastMode: false })).toBe("grok-3");
+  });
+});
diff --git a/src/agents/pi-embedded-runner/xai-stream-wrappers.ts b/src/agents/pi-embedded-runner/xai-stream-wrappers.ts
index 747c3fb4158..ceef1dcb36d 100644
--- a/src/agents/pi-embedded-runner/xai-stream-wrappers.ts
+++ b/src/agents/pi-embedded-runner/xai-stream-wrappers.ts
@@ -2,6 +2,8 @@ import type { StreamFn } from "@mariozechner/pi-agent-core";
 import { streamSimple } from "@mariozechner/pi-ai";
 
 const XAI_FAST_MODEL_IDS = new Map<string, string>([
+  ["grok-3", "grok-3-fast"],
+  ["grok-3-mini", "grok-3-mini-fast"],
   ["grok-4", "grok-4-fast"],
   ["grok-4-0709", "grok-4-fast"],
 ]);
diff --git a/src/agents/provider-capabilities.test.ts b/src/agents/provider-capabilities.test.ts
index 09f19468776..5dee5ea2113 100644
--- a/src/agents/provider-capabilities.test.ts
+++ b/src/agents/provider-capabilities.test.ts
@@ -53,6 +53,7 @@ import {
   shouldDropThinkingBlocksForModel,
   shouldSanitizeGeminiThoughtSignaturesForModel,
   supportsOpenAiCompatTurnValidation,
+  usesMoonshotThinkingPayloadCompat,
 } from "./provider-capabilities.js";
 
 describe("resolveProviderCapabilities", () => {
@@ -60,6 +61,7 @@ describe("resolveProviderCapabilities", () => {
     expect(resolveProviderCapabilities("anthropic")).toEqual({
       anthropicToolSchemaMode: "native",
       anthropicToolChoiceMode: "native",
+      openAiPayloadNormalizationMode: "default",
       providerFamily: "anthropic",
       preserveAnthropicThinkingSignatures: true,
       openAiCompatTurnValidation: true,
@@ -72,6 +74,7 @@ describe("resolveProviderCapabilities", () => {
     expect(resolveProviderCapabilities("anthropic-vertex")).toEqual({
       anthropicToolSchemaMode: "native",
       anthropicToolChoiceMode: "native",
+      openAiPayloadNormalizationMode: "default",
       providerFamily: "anthropic",
       preserveAnthropicThinkingSignatures: true,
       openAiCompatTurnValidation: true,
@@ -84,6 +87,7 @@ describe("resolveProviderCapabilities", () => {
     expect(resolveProviderCapabilities("amazon-bedrock")).toEqual({
       anthropicToolSchemaMode: "native",
       anthropicToolChoiceMode: "native",
+      openAiPayloadNormalizationMode: "default",
       providerFamily: "anthropic",
       preserveAnthropicThinkingSignatures: true,
       openAiCompatTurnValidation: true,
@@ -100,6 +104,7 @@ describe("resolveProviderCapabilities", () => {
     expect(resolveProviderCapabilities("kimi-code")).toEqual({
       anthropicToolSchemaMode: "native",
       anthropicToolChoiceMode: "native",
+      openAiPayloadNormalizationMode: "default",
       providerFamily: "default",
       preserveAnthropicThinkingSignatures: false,
       openAiCompatTurnValidation: true,
@@ -118,6 +123,11 @@ describe("resolveProviderCapabilities", () => {
     expect(supportsOpenAiCompatTurnValidation("moonshot")).toBe(true);
   });
 
+  it("routes moonshot payload compatibility through the capability registry", () => {
+    expect(usesMoonshotThinkingPayloadCompat("moonshot")).toBe(true);
+    expect(usesMoonshotThinkingPayloadCompat("openai")).toBe(false);
+  });
+
   it("resolves transcript thought-signature and tool-call quirks through the registry", () => {
     expect(
       shouldSanitizeGeminiThoughtSignaturesForModel({
diff --git a/src/agents/provider-capabilities.ts b/src/agents/provider-capabilities.ts
index c52be686387..01ec62f55f8 100644
--- a/src/agents/provider-capabilities.ts
+++ b/src/agents/provider-capabilities.ts
@@ -5,6 +5,7 @@ import { normalizeProviderId } from "./model-selection.js";
 export type ProviderCapabilities = {
   anthropicToolSchemaMode: "native" | "openai-functions";
   anthropicToolChoiceMode: "native" | "openai-string-modes";
+  openAiPayloadNormalizationMode: "default" | "moonshot-thinking";
   providerFamily: "default" | "openai" | "anthropic";
   preserveAnthropicThinkingSignatures: boolean;
   openAiCompatTurnValidation: boolean;
@@ -24,6 +25,7 @@ export type ProviderCapabilityLookupOptions = {
 const DEFAULT_PROVIDER_CAPABILITIES: ProviderCapabilities = {
   anthropicToolSchemaMode: "native",
   anthropicToolChoiceMode: "native",
+  openAiPayloadNormalizationMode: "default",
   providerFamily: "default",
   preserveAnthropicThinkingSignatures: true,
   openAiCompatTurnValidation: true,
@@ -62,6 +64,9 @@ const PLUGIN_CAPABILITIES_FALLBACKS: Record<string, Partial<ProviderCapabilities
       "mistralai",
     ],
   },
+  moonshot: {
+    openAiPayloadNormalizationMode: "moonshot-thinking",
+  },
   opencode: {
     openAiCompatTurnValidation: false,
     geminiThoughtSignatureSanitization: true,
@@ -140,6 +145,16 @@ export function supportsOpenAiCompatTurnValidation(
   return resolveProviderCapabilities(provider, options).openAiCompatTurnValidation;
 }
 
+export function usesMoonshotThinkingPayloadCompat(
+  provider?: string | null,
+  options?: ProviderCapabilityLookupOptions,
+): boolean {
+  return (
+    resolveProviderCapabilities(provider, options).openAiPayloadNormalizationMode ===
+    "moonshot-thinking"
+  );
+}
+
 export function sanitizesGeminiThoughtSignatures(
   provider?: string | null,
   options?: ProviderCapabilityLookupOptions,