diff --git a/src/server/proxy-core/providers/codexProviderProfile.ts b/src/server/proxy-core/providers/codexProviderProfile.ts
index 8db4176..c0a06e2 100644
--- a/src/server/proxy-core/providers/codexProviderProfile.ts
+++ b/src/server/proxy-core/providers/codexProviderProfile.ts
@@ -20,6 +20,7 @@ export const codexProviderProfile: ProviderProfile = {
     const headers = buildCodexRuntimeHeaders({
       baseHeaders: input.baseHeaders,
       providerHeaders: input.providerHeaders,
+      stream: input.stream,
       explicitSessionId: asTrimmedString(input.codexExplicitSessionId) || null,
       continuityKey: asTrimmedString(input.codexSessionCacheKey) || null,
       userAgentOverride: configuredUserAgent || null,
diff --git a/src/server/proxy-core/providers/headerUtils.test.ts b/src/server/proxy-core/providers/headerUtils.test.ts
index b1c4398..a18f60a 100644
--- a/src/server/proxy-core/providers/headerUtils.test.ts
+++ b/src/server/proxy-core/providers/headerUtils.test.ts
@@ -61,6 +61,7 @@ describe('provider header utils', () => {
         originator: 'codex_cli_rs',
         'chatgpt-account-id': 'acct-1',
       },
+      stream: false,
       continuityKey: 'cache-key-1',
       explicitSessionId: null,
     });
@@ -70,7 +71,7 @@ describe('provider header utils', () => {
     expect(headers['Chatgpt-Account-Id']).toBe('acct-1');
     expect(headers.Session_id).toMatch(/^[0-9a-f-]{36}$/);
     expect(headers.Conversation_id).toBe(headers.Session_id);
-    expect(headers.Accept).toBe('text/event-stream');
+    expect(headers.Accept).toBe('application/json');
   });
 
   it('builds claude runtime headers with merged betas and oauth bearer auth', async () => {
diff --git a/src/server/proxy-core/providers/headerUtils.ts b/src/server/proxy-core/providers/headerUtils.ts
index 5846694..f37e9a3 100644
--- a/src/server/proxy-core/providers/headerUtils.ts
+++ b/src/server/proxy-core/providers/headerUtils.ts
@@ -114,6 +114,7 @@ function asTrimmedString(value: unknown): string {
 export function buildCodexRuntimeHeaders(input: {
   baseHeaders: Record<string, string>;
   providerHeaders?: Record<string, string>;
+  stream?: boolean;
   explicitSessionId?: string | null;
   continuityKey?: string | null;
   versionDefault?: string;
@@ -177,7 +178,7 @@ export function buildCodexRuntimeHeaders(input: {
     Session_id: sessionId,
     ...(conversationId ? { Conversation_id: conversationId } : {}),
     'User-Agent': userAgent,
-    Accept: 'text/event-stream',
+    Accept: input.stream === false ? 'application/json' : 'text/event-stream',
     Connection: 'Keep-Alive',
   };
 }
diff --git a/src/server/routes/proxy/responses.compact-upstream.test.ts b/src/server/routes/proxy/responses.compact-upstream.test.ts
index 808dc76..d7dc3c1 100644
--- a/src/server/routes/proxy/responses.compact-upstream.test.ts
+++ b/src/server/routes/proxy/responses.compact-upstream.test.ts
@@ -362,6 +362,7 @@ describe('responses proxy compact upstream routing', () => {
     expect(forwardedBody.stream_options).toBeUndefined();
     expect(forwardedBody.instructions).toBe('');
     expect(forwardedBody.store).toBe(false);
+    expect(options.headers.Accept || options.headers.accept).toBe('application/json');
   });
 
   it('preserves native response.compaction payloads instead of coercing them into object=response', async () => {
diff --git a/src/server/routes/proxy/upstreamEndpoint.test.ts b/src/server/routes/proxy/upstreamEndpoint.test.ts
index 358a2d8..fb92665 100644
--- a/src/server/routes/proxy/upstreamEndpoint.test.ts
+++ b/src/server/routes/proxy/upstreamEndpoint.test.ts
@@ -815,7 +815,7 @@ describe('buildUpstreamEndpointRequest', () => {
     expect(request.headers.Session_id).toMatch(/^[0-9a-f-]{36}$/i);
     expect(request.headers.Conversation_id).toBe(request.headers.Session_id);
     expect(request.headers['User-Agent']).toBe('codex_cli_rs/0.101.0 (Mac OS 26.0.1; arm64) Apple_Terminal/464');
-    expect(request.headers.Accept).toBe('text/event-stream');
+    expect(request.headers.Accept).toBe('application/json');
     expect(request.headers.Connection).toBe('Keep-Alive');
     expect(request.body.instructions).toBe('');
     expect(request.body.prompt_cache_key).toBeUndefined();