diff --git a/src/main/claude/pi-model-resolution.ts b/src/main/claude/pi-model-resolution.ts
index 15fba88e..c283ef45 100644
--- a/src/main/claude/pi-model-resolution.ts
+++ b/src/main/claude/pi-model-resolution.ts
@@ -41,7 +41,11 @@ export interface SyntheticPiModelFallback {
 
 export function resolvePiRouteProtocol(provider?: string, customProtocol?: string): string {
   if (provider === 'custom') {
-    if (customProtocol === 'openai' || customProtocol === 'gemini') {
+    if (
+      customProtocol === 'openai' ||
+      customProtocol === 'openai-responses' ||
+      customProtocol === 'gemini'
+    ) {
       return customProtocol;
     }
     return 'anthropic';
@@ -76,6 +80,8 @@ export function inferPiApi(protocol: string): string {
     case 'gemini':
     case 'google':
       return 'google-generative-ai';
+    case 'openai-responses':
+      return 'openai-responses';
     case 'openai':
     default:
       return 'openai-completions';
@@ -267,10 +273,26 @@ export function applyPiModelRuntimeOverrides(
   }
 
   const effectiveProvider = options.rawProvider || options.configProvider;
-  if (options.customBaseUrl && isCustomProvider && nextModel.api === 'openai-responses') {
-    // Most custom OpenAI-compatible relays only implement chat/completions.
+  if (
+    options.customBaseUrl &&
+    isCustomProvider &&
+    nextModel.api === 'openai-responses' &&
+    options.customProtocol !== 'openai-responses'
+  ) {
+    // Most custom OpenAI-compatible relays only implement chat/completions, so
+    // downgrade by default. Skip the downgrade when the user has explicitly
+    // chosen 'openai-responses' as the customProtocol — that's an opt-in signal
+    // that their relay implements the Responses API.
     nextModel = { ...nextModel, api: 'openai-completions' } as typeof nextModel;
   }
+  if (
+    isCustomProvider &&
+    options.customProtocol === 'openai-responses' &&
+    nextModel.api !== 'openai-responses'
+  ) {
+    // User explicitly opted in to Responses API for this custom relay.
+    nextModel = { ...nextModel, api: 'openai-responses' } as typeof nextModel;
+  }
   if (effectiveProvider === 'openrouter' && nextModel.api !== 'openai-completions') {
     nextModel = { ...nextModel, api: 'openai-completions' } as typeof nextModel;
   }
diff --git a/src/main/config/config-store.ts b/src/main/config/config-store.ts
index 6308fa44..f7983636 100644
--- a/src/main/config/config-store.ts
+++ b/src/main/config/config-store.ts
@@ -35,7 +35,7 @@ import { API_PROVIDER_PRESETS, PI_AI_CURATED_PRESETS } from '../../shared/api-mo
  * Application configuration schema
  */
 export type ProviderType = 'openrouter' | 'anthropic' | 'custom' | 'openai' | 'gemini' | 'ollama';
-export type CustomProtocolType = 'anthropic' | 'openai' | 'gemini';
+export type CustomProtocolType = 'anthropic' | 'openai' | 'openai-responses' | 'gemini';
 export type AppTheme = 'dark' | 'light' | 'system';
 export type ProviderProfileKey =
   | 'openrouter'
@@ -293,7 +293,12 @@ function isProviderType(value: unknown): value is ProviderType {
 }
 
 function isCustomProtocol(value: unknown): value is CustomProtocolType {
-  return value === 'anthropic' || value === 'openai' || value === 'gemini';
+  return (
+    value === 'anthropic' ||
+    value === 'openai' ||
+    value === 'openai-responses' ||
+    value === 'gemini'
+  );
 }
 
 function isProfileKey(value: unknown): value is ProviderProfileKey {
@@ -311,7 +316,10 @@ function profileKeyFromProvider(
   if (provider !== 'custom') {
     return provider;
   }
-  if (customProtocol === 'openai') {
+  if (customProtocol === 'openai' || customProtocol === 'openai-responses') {
+    // openai-responses shares the profile slot with openai (same baseUrl/key,
+    // different request shape). Avoids forcing the user to re-enter creds when
+    // toggling between the two protocols on the same relay.
     return 'custom:openai';
   }
   if (customProtocol === 'gemini') {
diff --git a/src/renderer/types/index.ts b/src/renderer/types/index.ts
index 06f5cadb..04ec9e76 100644
--- a/src/renderer/types/index.ts
+++ b/src/renderer/types/index.ts
@@ -428,7 +428,7 @@ export interface ExecutionContext {
 
 // App Config types
 export type ProviderType = 'openrouter' | 'anthropic' | 'custom' | 'openai' | 'gemini' | 'ollama';
-export type CustomProtocolType = 'anthropic' | 'openai' | 'gemini';
+export type CustomProtocolType = 'anthropic' | 'openai' | 'openai-responses' | 'gemini';
 export type AppTheme = 'dark' | 'light' | 'system';
 export type ProviderProfileKey =
   | 'openrouter'
diff --git a/src/shared/api-model-presets.ts b/src/shared/api-model-presets.ts
index 2ac15700..733b5bfa 100644
--- a/src/shared/api-model-presets.ts
+++ b/src/shared/api-model-presets.ts
@@ -6,7 +6,7 @@ export type SharedProviderType =
   | 'gemini'
   | 'ollama';
 
-export type SharedCustomProtocolType = 'anthropic' | 'openai' | 'gemini';
+export type SharedCustomProtocolType = 'anthropic' | 'openai' | 'openai-responses' | 'gemini';
 
 export interface SharedProviderPreset {
   name: string;