diff --git a/types/defines/ai.d.ts b/types/defines/ai.d.ts
index c8fb8437c0b..f1d2547b201 100644
--- a/types/defines/ai.d.ts
+++ b/types/defines/ai.d.ts
@@ -632,12 +632,11 @@ export type ChatCompletionChoice = {
   finish_reason: "stop" | "length" | "tool_calls" | "content_filter" | "function_call";
   logprobs: ChatCompletionLogprobs | null;
 };
-export type ChatCompletionsPromptInput = {
-  prompt: string;
-} & ChatCompletionsCommonOptions;
+
 export type ChatCompletionsMessagesInput = {
   messages: Array<ChatCompletionMessageParam>;
 } & ChatCompletionsCommonOptions;
+
 export type ChatCompletionsOutput = {
   id: string;
   object: string;
@@ -648,6 +647,7 @@ export type ChatCompletionsOutput = {
   system_fingerprint?: string | null;
   service_tier?: "auto" | "default" | "flex" | "scale" | "priority" | null;
 };
+
 /**
  * Workers AI support for OpenAI's Responses API
  * Reference: https://github.com/openai/openai-node/blob/master/src/resources/responses/responses.ts
@@ -4730,11 +4730,11 @@ export declare abstract class Base_Ai_Cf_Pipecat_Ai_Smart_Turn_V2 {
   postProcessedOutputs: Ai_Cf_Pipecat_Ai_Smart_Turn_V2_Output;
 }
 export declare abstract class Base_Ai_Cf_Openai_Gpt_Oss_120B {
-  inputs: XOR<ResponsesInput, ChatCompletionsInput>;
+  inputs: XOR<ResponsesInput, ChatCompletionsMessagesInput>;
   postProcessedOutputs: XOR<ResponsesOutput, ChatCompletionsOutput>;
 }
 export declare abstract class Base_Ai_Cf_Openai_Gpt_Oss_20B {
-  inputs: XOR<ResponsesInput, ChatCompletionsInput>;
+  inputs: XOR<ResponsesInput, ChatCompletionsMessagesInput>;
   postProcessedOutputs: XOR<ResponsesOutput, ChatCompletionsOutput>;
 }
 export interface Ai_Cf_Leonardo_Phoenix_1_0_Input {
@@ -5824,7 +5824,7 @@ export declare abstract class Base_Ai_Cf_Moonshotai_Kimi_K2_5 {
   postProcessedOutputs: ChatCompletionsOutput;
 }
 export declare abstract class Base_Ai_Cf_Moonshotai_Kimi_K2_6 {
-  inputs: ChatCompletionsBase;
+  inputs: ChatCompletionsInput;
   postProcessedOutputs: ChatCompletionsOutput;
 }
 export declare abstract class Base_Ai_Cf_Nvidia_Nemotron_3_120B_A12B {
@@ -5832,9 +5832,10 @@ export declare abstract class Base_Ai_Cf_Nvidia_Nemotron_3_120B_A12B {
   postProcessedOutputs: ChatCompletionsOutput;
 }
 export declare abstract class Base_Ai_Cf_Google_Gemma_4_26B_A4B_IT {
-  inputs: ChatCompletionsBase;
+  inputs: ChatCompletionsInput;
   postProcessedOutputs: ChatCompletionsOutput;
 }
+
 export interface AiModels {
   "@cf/huggingface/distilbert-sst-2-int8": BaseAiTextClassification;
   "@cf/stabilityai/stable-diffusion-xl-base-1.0": BaseAiTextToImage;
@@ -5979,13 +5980,10 @@ export type AiModelsSearchObject = {
     value: string;
   }[];
 };
-export type ChatCompletionsBase = XOR<ChatCompletionsPromptInput, ChatCompletionsMessagesInput>;
-export type ChatCompletionsInput = XOR<
-  ChatCompletionsBase,
-  {
-    requests: ChatCompletionsBase[];
-  }
->;
+
+export type ChatCompletionsBase = ChatCompletionsMessagesInput;
+export type ChatCompletionsInput = ChatCompletionsMessagesInput;
+
 export interface InferenceUpstreamError extends Error {}
 export interface AiInternalError extends Error {}
 export type AiModelListType = Record<string, any>;
@@ -6046,9 +6044,16 @@ export declare abstract class Ai<
     options?: AiOptions
   ): Promise<AiModelList[Name]['postProcessedOutputs']>;
 
-  // Unknown model (gateway fallback)
-  run(
-    model: string & {},
+  // Unknown model (fallback).
+  //
+  // The `Exclude<..., keyof AiModelList>` constraint forces TypeScript to
+  // route any model name that is a literal key of `AiModelList` to one of
+  // the known-model overloads above (so input/output mismatches surface as
+  // type errors rather than silently falling back to `Record<string, unknown>`).
+  // Names that aren't in `AiModelList` — e.g. third-party gateway models
+  // like `"google/nano-banana"` — still hit this overload.
+  run<Model extends string>(
+    model: Model extends keyof AiModelList ? never : Model,
     inputs: Record<string, unknown>,
     options?: AiOptions
   ): Promise<Record<string, unknown>>;
diff --git a/types/generated-snapshot/experimental/index.d.ts b/types/generated-snapshot/experimental/index.d.ts
index 85f9cb25e56..cec7eee584d 100755
--- a/types/generated-snapshot/experimental/index.d.ts
+++ b/types/generated-snapshot/experimental/index.d.ts
@@ -6177,9 +6177,6 @@ type ChatCompletionChoice = {
     | "function_call";
   logprobs: ChatCompletionLogprobs | null;
 };
-type ChatCompletionsPromptInput = {
-  prompt: string;
-} & ChatCompletionsCommonOptions;
 type ChatCompletionsMessagesInput = {
   messages: Array<ChatCompletionMessageParam>;
 } & ChatCompletionsCommonOptions;
@@ -10304,11 +10301,11 @@ declare abstract class Base_Ai_Cf_Pipecat_Ai_Smart_Turn_V2 {
   postProcessedOutputs: Ai_Cf_Pipecat_Ai_Smart_Turn_V2_Output;
 }
 declare abstract class Base_Ai_Cf_Openai_Gpt_Oss_120B {
-  inputs: XOR<ResponsesInput, ChatCompletionsInput>;
+  inputs: XOR<ResponsesInput, ChatCompletionsMessagesInput>;
   postProcessedOutputs: XOR<ResponsesOutput, ChatCompletionsOutput>;
 }
 declare abstract class Base_Ai_Cf_Openai_Gpt_Oss_20B {
-  inputs: XOR<ResponsesInput, ChatCompletionsInput>;
+  inputs: XOR<ResponsesInput, ChatCompletionsMessagesInput>;
   postProcessedOutputs: XOR<ResponsesOutput, ChatCompletionsOutput>;
 }
 interface Ai_Cf_Leonardo_Phoenix_1_0_Input {
@@ -11403,7 +11400,7 @@ declare abstract class Base_Ai_Cf_Moonshotai_Kimi_K2_5 {
   postProcessedOutputs: ChatCompletionsOutput;
 }
 declare abstract class Base_Ai_Cf_Moonshotai_Kimi_K2_6 {
-  inputs: ChatCompletionsBase;
+  inputs: ChatCompletionsInput;
   postProcessedOutputs: ChatCompletionsOutput;
 }
 declare abstract class Base_Ai_Cf_Nvidia_Nemotron_3_120B_A12B {
@@ -11411,7 +11408,7 @@ declare abstract class Base_Ai_Cf_Nvidia_Nemotron_3_120B_A12B {
   postProcessedOutputs: ChatCompletionsOutput;
 }
 declare abstract class Base_Ai_Cf_Google_Gemma_4_26B_A4B_IT {
-  inputs: ChatCompletionsBase;
+  inputs: ChatCompletionsInput;
   postProcessedOutputs: ChatCompletionsOutput;
 }
 interface AiModels {
@@ -11558,16 +11555,8 @@ type AiModelsSearchObject = {
     value: string;
   }[];
 };
-type ChatCompletionsBase = XOR<
-  ChatCompletionsPromptInput,
-  ChatCompletionsMessagesInput
->;
-type ChatCompletionsInput = XOR<
-  ChatCompletionsBase,
-  {
-    requests: ChatCompletionsBase[];
-  }
->;
+type ChatCompletionsBase = ChatCompletionsMessagesInput;
+type ChatCompletionsInput = ChatCompletionsMessagesInput;
 interface InferenceUpstreamError extends Error {}
 interface AiInternalError extends Error {}
 type AiModelListType = Record<string, any>;
@@ -11630,9 +11619,16 @@ declare abstract class Ai<AiModelList extends AiModelListType = AiModels> {
     inputs: AiModelList[Name]["inputs"],
     options?: AiOptions,
   ): Promise<AiModelList[Name]["postProcessedOutputs"]>;
-  // Unknown model (gateway fallback)
-  run(
-    model: string & {},
+  // Unknown model (fallback).
+  //
+  // The `Exclude<..., keyof AiModelList>` constraint forces TypeScript to
+  // route any model name that is a literal key of `AiModelList` to one of
+  // the known-model overloads above (so input/output mismatches surface as
+  // type errors rather than silently falling back to `Record<string, unknown>`).
+  // Names that aren't in `AiModelList` — e.g. third-party gateway models
+  // like `"google/nano-banana"` — still hit this overload.
+  run<Model extends string>(
+    model: Model extends keyof AiModelList ? never : Model,
     inputs: Record<string, unknown>,
     options?: AiOptions,
   ): Promise<Record<string, unknown>>;
diff --git a/types/generated-snapshot/experimental/index.ts b/types/generated-snapshot/experimental/index.ts
index d8afd32e79c..5f1fae81a1e 100755
--- a/types/generated-snapshot/experimental/index.ts
+++ b/types/generated-snapshot/experimental/index.ts
@@ -6186,9 +6186,6 @@ export type ChatCompletionChoice = {
     | "function_call";
   logprobs: ChatCompletionLogprobs | null;
 };
-export type ChatCompletionsPromptInput = {
-  prompt: string;
-} & ChatCompletionsCommonOptions;
 export type ChatCompletionsMessagesInput = {
   messages: Array<ChatCompletionMessageParam>;
 } & ChatCompletionsCommonOptions;
@@ -10314,11 +10311,11 @@ export declare abstract class Base_Ai_Cf_Pipecat_Ai_Smart_Turn_V2 {
   postProcessedOutputs: Ai_Cf_Pipecat_Ai_Smart_Turn_V2_Output;
 }
 export declare abstract class Base_Ai_Cf_Openai_Gpt_Oss_120B {
-  inputs: XOR<ResponsesInput, ChatCompletionsInput>;
+  inputs: XOR<ResponsesInput, ChatCompletionsMessagesInput>;
   postProcessedOutputs: XOR<ResponsesOutput, ChatCompletionsOutput>;
 }
 export declare abstract class Base_Ai_Cf_Openai_Gpt_Oss_20B {
-  inputs: XOR<ResponsesInput, ChatCompletionsInput>;
+  inputs: XOR<ResponsesInput, ChatCompletionsMessagesInput>;
   postProcessedOutputs: XOR<ResponsesOutput, ChatCompletionsOutput>;
 }
 export interface Ai_Cf_Leonardo_Phoenix_1_0_Input {
@@ -11413,7 +11410,7 @@ export declare abstract class Base_Ai_Cf_Moonshotai_Kimi_K2_5 {
   postProcessedOutputs: ChatCompletionsOutput;
 }
 export declare abstract class Base_Ai_Cf_Moonshotai_Kimi_K2_6 {
-  inputs: ChatCompletionsBase;
+  inputs: ChatCompletionsInput;
   postProcessedOutputs: ChatCompletionsOutput;
 }
 export declare abstract class Base_Ai_Cf_Nvidia_Nemotron_3_120B_A12B {
@@ -11421,7 +11418,7 @@ export declare abstract class Base_Ai_Cf_Nvidia_Nemotron_3_120B_A12B {
   postProcessedOutputs: ChatCompletionsOutput;
 }
 export declare abstract class Base_Ai_Cf_Google_Gemma_4_26B_A4B_IT {
-  inputs: ChatCompletionsBase;
+  inputs: ChatCompletionsInput;
   postProcessedOutputs: ChatCompletionsOutput;
 }
 export interface AiModels {
@@ -11568,16 +11565,8 @@ export type AiModelsSearchObject = {
     value: string;
   }[];
 };
-export type ChatCompletionsBase = XOR<
-  ChatCompletionsPromptInput,
-  ChatCompletionsMessagesInput
->;
-export type ChatCompletionsInput = XOR<
-  ChatCompletionsBase,
-  {
-    requests: ChatCompletionsBase[];
-  }
->;
+export type ChatCompletionsBase = ChatCompletionsMessagesInput;
+export type ChatCompletionsInput = ChatCompletionsMessagesInput;
 export interface InferenceUpstreamError extends Error {}
 export interface AiInternalError extends Error {}
 export type AiModelListType = Record<string, any>;
@@ -11642,9 +11631,16 @@ export declare abstract class Ai<
     inputs: AiModelList[Name]["inputs"],
     options?: AiOptions,
   ): Promise<AiModelList[Name]["postProcessedOutputs"]>;
-  // Unknown model (gateway fallback)
-  run(
-    model: string & {},
+  // Unknown model (fallback).
+  //
+  // The `Exclude<..., keyof AiModelList>` constraint forces TypeScript to
+  // route any model name that is a literal key of `AiModelList` to one of
+  // the known-model overloads above (so input/output mismatches surface as
+  // type errors rather than silently falling back to `Record<string, unknown>`).
+  // Names that aren't in `AiModelList` — e.g. third-party gateway models
+  // like `"google/nano-banana"` — still hit this overload.
+  run<Model extends string>(
+    model: Model extends keyof AiModelList ? never : Model,
     inputs: Record<string, unknown>,
     options?: AiOptions,
   ): Promise<Record<string, unknown>>;
diff --git a/types/generated-snapshot/latest/index.d.ts b/types/generated-snapshot/latest/index.d.ts
index 9dd7f83b0da..89be26c5556 100755
--- a/types/generated-snapshot/latest/index.d.ts
+++ b/types/generated-snapshot/latest/index.d.ts
@@ -5509,9 +5509,6 @@ type ChatCompletionChoice = {
     | "function_call";
   logprobs: ChatCompletionLogprobs | null;
 };
-type ChatCompletionsPromptInput = {
-  prompt: string;
-} & ChatCompletionsCommonOptions;
 type ChatCompletionsMessagesInput = {
   messages: Array<ChatCompletionMessageParam>;
 } & ChatCompletionsCommonOptions;
@@ -9636,11 +9633,11 @@ declare abstract class Base_Ai_Cf_Pipecat_Ai_Smart_Turn_V2 {
   postProcessedOutputs: Ai_Cf_Pipecat_Ai_Smart_Turn_V2_Output;
 }
 declare abstract class Base_Ai_Cf_Openai_Gpt_Oss_120B {
-  inputs: XOR<ResponsesInput, ChatCompletionsInput>;
+  inputs: XOR<ResponsesInput, ChatCompletionsMessagesInput>;
   postProcessedOutputs: XOR<ResponsesOutput, ChatCompletionsOutput>;
 }
 declare abstract class Base_Ai_Cf_Openai_Gpt_Oss_20B {
-  inputs: XOR<ResponsesInput, ChatCompletionsInput>;
+  inputs: XOR<ResponsesInput, ChatCompletionsMessagesInput>;
   postProcessedOutputs: XOR<ResponsesOutput, ChatCompletionsOutput>;
 }
 interface Ai_Cf_Leonardo_Phoenix_1_0_Input {
@@ -10735,7 +10732,7 @@ declare abstract class Base_Ai_Cf_Moonshotai_Kimi_K2_5 {
   postProcessedOutputs: ChatCompletionsOutput;
 }
 declare abstract class Base_Ai_Cf_Moonshotai_Kimi_K2_6 {
-  inputs: ChatCompletionsBase;
+  inputs: ChatCompletionsInput;
   postProcessedOutputs: ChatCompletionsOutput;
 }
 declare abstract class Base_Ai_Cf_Nvidia_Nemotron_3_120B_A12B {
@@ -10743,7 +10740,7 @@ declare abstract class Base_Ai_Cf_Nvidia_Nemotron_3_120B_A12B {
   postProcessedOutputs: ChatCompletionsOutput;
 }
 declare abstract class Base_Ai_Cf_Google_Gemma_4_26B_A4B_IT {
-  inputs: ChatCompletionsBase;
+  inputs: ChatCompletionsInput;
   postProcessedOutputs: ChatCompletionsOutput;
 }
 interface AiModels {
@@ -10890,16 +10887,8 @@ type AiModelsSearchObject = {
     value: string;
   }[];
 };
-type ChatCompletionsBase = XOR<
-  ChatCompletionsPromptInput,
-  ChatCompletionsMessagesInput
->;
-type ChatCompletionsInput = XOR<
-  ChatCompletionsBase,
-  {
-    requests: ChatCompletionsBase[];
-  }
->;
+type ChatCompletionsBase = ChatCompletionsMessagesInput;
+type ChatCompletionsInput = ChatCompletionsMessagesInput;
 interface InferenceUpstreamError extends Error {}
 interface AiInternalError extends Error {}
 type AiModelListType = Record<string, any>;
@@ -10962,9 +10951,16 @@ declare abstract class Ai<AiModelList extends AiModelListType = AiModels> {
     inputs: AiModelList[Name]["inputs"],
     options?: AiOptions,
   ): Promise<AiModelList[Name]["postProcessedOutputs"]>;
-  // Unknown model (gateway fallback)
-  run(
-    model: string & {},
+  // Unknown model (fallback).
+  //
+  // The `Exclude<..., keyof AiModelList>` constraint forces TypeScript to
+  // route any model name that is a literal key of `AiModelList` to one of
+  // the known-model overloads above (so input/output mismatches surface as
+  // type errors rather than silently falling back to `Record<string, unknown>`).
+  // Names that aren't in `AiModelList` — e.g. third-party gateway models
+  // like `"google/nano-banana"` — still hit this overload.
+  run<Model extends string>(
+    model: Model extends keyof AiModelList ? never : Model,
     inputs: Record<string, unknown>,
     options?: AiOptions,
   ): Promise<Record<string, unknown>>;
diff --git a/types/generated-snapshot/latest/index.ts b/types/generated-snapshot/latest/index.ts
index 4fdac7047be..4c2fdb200d5 100755
--- a/types/generated-snapshot/latest/index.ts
+++ b/types/generated-snapshot/latest/index.ts
@@ -5518,9 +5518,6 @@ export type ChatCompletionChoice = {
     | "function_call";
   logprobs: ChatCompletionLogprobs | null;
 };
-export type ChatCompletionsPromptInput = {
-  prompt: string;
-} & ChatCompletionsCommonOptions;
 export type ChatCompletionsMessagesInput = {
   messages: Array<ChatCompletionMessageParam>;
 } & ChatCompletionsCommonOptions;
@@ -9646,11 +9643,11 @@ export declare abstract class Base_Ai_Cf_Pipecat_Ai_Smart_Turn_V2 {
   postProcessedOutputs: Ai_Cf_Pipecat_Ai_Smart_Turn_V2_Output;
 }
 export declare abstract class Base_Ai_Cf_Openai_Gpt_Oss_120B {
-  inputs: XOR<ResponsesInput, ChatCompletionsInput>;
+  inputs: XOR<ResponsesInput, ChatCompletionsMessagesInput>;
   postProcessedOutputs: XOR<ResponsesOutput, ChatCompletionsOutput>;
 }
 export declare abstract class Base_Ai_Cf_Openai_Gpt_Oss_20B {
-  inputs: XOR<ResponsesInput, ChatCompletionsInput>;
+  inputs: XOR<ResponsesInput, ChatCompletionsMessagesInput>;
   postProcessedOutputs: XOR<ResponsesOutput, ChatCompletionsOutput>;
 }
 export interface Ai_Cf_Leonardo_Phoenix_1_0_Input {
@@ -10745,7 +10742,7 @@ export declare abstract class Base_Ai_Cf_Moonshotai_Kimi_K2_5 {
   postProcessedOutputs: ChatCompletionsOutput;
 }
 export declare abstract class Base_Ai_Cf_Moonshotai_Kimi_K2_6 {
-  inputs: ChatCompletionsBase;
+  inputs: ChatCompletionsInput;
   postProcessedOutputs: ChatCompletionsOutput;
 }
 export declare abstract class Base_Ai_Cf_Nvidia_Nemotron_3_120B_A12B {
@@ -10753,7 +10750,7 @@ export declare abstract class Base_Ai_Cf_Nvidia_Nemotron_3_120B_A12B {
   postProcessedOutputs: ChatCompletionsOutput;
 }
 export declare abstract class Base_Ai_Cf_Google_Gemma_4_26B_A4B_IT {
-  inputs: ChatCompletionsBase;
+  inputs: ChatCompletionsInput;
   postProcessedOutputs: ChatCompletionsOutput;
 }
 export interface AiModels {
@@ -10900,16 +10897,8 @@ export type AiModelsSearchObject = {
     value: string;
   }[];
 };
-export type ChatCompletionsBase = XOR<
-  ChatCompletionsPromptInput,
-  ChatCompletionsMessagesInput
->;
-export type ChatCompletionsInput = XOR<
-  ChatCompletionsBase,
-  {
-    requests: ChatCompletionsBase[];
-  }
->;
+export type ChatCompletionsBase = ChatCompletionsMessagesInput;
+export type ChatCompletionsInput = ChatCompletionsMessagesInput;
 export interface InferenceUpstreamError extends Error {}
 export interface AiInternalError extends Error {}
 export type AiModelListType = Record<string, any>;
@@ -10974,9 +10963,16 @@ export declare abstract class Ai<
     inputs: AiModelList[Name]["inputs"],
     options?: AiOptions,
   ): Promise<AiModelList[Name]["postProcessedOutputs"]>;
-  // Unknown model (gateway fallback)
-  run(
-    model: string & {},
+  // Unknown model (fallback).
+  //
+  // The `Exclude<..., keyof AiModelList>` constraint forces TypeScript to
+  // route any model name that is a literal key of `AiModelList` to one of
+  // the known-model overloads above (so input/output mismatches surface as
+  // type errors rather than silently falling back to `Record<string, unknown>`).
+  // Names that aren't in `AiModelList` — e.g. third-party gateway models
+  // like `"google/nano-banana"` — still hit this overload.
+  run<Model extends string>(
+    model: Model extends keyof AiModelList ? never : Model,
     inputs: Record<string, unknown>,
     options?: AiOptions,
   ): Promise<Record<string, unknown>>;
diff --git a/types/test/types/ai.ts b/types/test/types/ai.ts
index a8ad0ff7bb3..6eab9658521 100644
--- a/types/test/types/ai.ts
+++ b/types/test/types/ai.ts
@@ -4,6 +4,7 @@
 
 function expectType<T>(_value: T) {}
 
+
 export const handler: ExportedHandler<{ AI: Ai }> = {
   async fetch(_request, env) {
     // Known model -- normal response
@@ -62,6 +63,19 @@ export const handler: ExportedHandler<{ AI: Ai }> = {
       expectType<Record<string, unknown>>(result);
     }
 
+    // Known model names do not silently fall through to the unknown-model
+    // gateway-fallback overload. The fallback's signature excludes
+    // `keyof AiModelList`, so a call with a known model name and an input
+    // shape that doesn't match the known-model overload must surface as a
+    // type error rather than degrading to `Record<string, unknown>`. Here
+    // we exercise that with kimi-k2.6, whose typed input is
+    // `ChatCompletionsMessagesInput` (no `prompt` field).
+    {
+      // @ts-expect-error: kimi-k2.6 takes `messages`, not `prompt`; the
+      // unknown-model fallback must not catch this call.
+      await env.AI.run('@cf/moonshotai/kimi-k2.6', { prompt: 'hello' });
+    }
+
     return new Response();
   },
 };