diff --git a/open-sse/handlers/chatCore.ts b/open-sse/handlers/chatCore.ts
index 77f2ba0ddc..81e97f1c98 100644
--- a/open-sse/handlers/chatCore.ts
+++ b/open-sse/handlers/chatCore.ts
@@ -1920,7 +1920,15 @@ export async function handleChatCore({
 
   let translatedBody = body;
   const isClaudePassthrough = sourceFormat === FORMATS.CLAUDE && targetFormat === FORMATS.CLAUDE;
-  const isClaudeCodeCompatible = isClaudeCodeCompatibleProvider(provider);
+  // A provider may expose the Claude Code wire image as its default protocol while
+  // selecting a declared OpenAI alternate on a connection (for example AgentRouter).
+  // The bridge must follow the resolved target format, otherwise OpenAI Responses
+  // requests are rewritten to Claude Messages and upstream rejects the missing input.
+  const configuredTargetFormat = credentials?.providerSpecificData?.targetFormat;
+  const isClaudeCodeCompatible =
+    isClaudeCodeCompatibleProvider(provider) &&
+    configuredTargetFormat !== FORMATS.OPENAI &&
+    configuredTargetFormat !== FORMATS.OPENAI_RESPONSES;
   const isClaudeCodeSemanticPassthrough = isClaudeCodeSemanticPassthroughRequest({
     provider,
     sourceFormat,
diff --git a/tests/unit/agentrouter-chatcore-protocols.test.ts b/tests/unit/agentrouter-chatcore-protocols.test.ts
new file mode 100644
index 0000000000..87a539643e
--- /dev/null
+++ b/tests/unit/agentrouter-chatcore-protocols.test.ts
@@ -0,0 +1,239 @@
+// @ts-nocheck
+import assert from "node:assert/strict";
+import fs from "node:fs";
+import os from "node:os";
+import path from "node:path";
+import test from "node:test";
+
+const TEST_DATA_DIR = fs.mkdtempSync(path.join(os.tmpdir(), "omniroute-agentrouter-chatcore-"));
+process.env.DATA_DIR = TEST_DATA_DIR;
+
+const core = await import("../../src/lib/db/core.ts");
+const { handleChatCore } = await import("../../open-sse/handlers/chatCore.ts");
+
+const originalFetch = globalThis.fetch;
+
+function noopLog() {
+  return {
+    debug() {},
+    info() {},
+    warn() {},
+    error() {},
+  };
+}
+
+async function waitForAsyncSideEffects() {
+  await new Promise((resolve) => setImmediate(resolve));
+  await new Promise((resolve) => setTimeout(resolve, 20));
+}
+
+test.afterEach(async () => {
+  globalThis.fetch = originalFetch;
+  await waitForAsyncSideEffects();
+  core.resetDbInstance();
+  fs.rmSync(TEST_DATA_DIR, { recursive: true, force: true });
+  fs.mkdirSync(TEST_DATA_DIR, { recursive: true });
+});
+
+test.after(() => {
+  globalThis.fetch = originalFetch;
+  core.resetDbInstance();
+  fs.rmSync(TEST_DATA_DIR, { recursive: true, force: true });
+});
+
+test("AgentRouter Responses connections send a native Responses body through chatCore", async () => {
+  let captured: { url: string; headers: Headers; body: Record<string, unknown> } | null = null;
+
+  globalThis.fetch = async (url, init = {}) => {
+    const body = JSON.parse(String(init.body || "{}"));
+    captured = {
+      url: String(url),
+      headers: new Headers(init.headers),
+      body,
+    };
+
+    if (!("input" in body)) {
+      return new Response(JSON.stringify({ error: { message: "input is required" } }), {
+        status: 400,
+        headers: { "Content-Type": "application/json" },
+      });
+    }
+
+    return new Response(
+      JSON.stringify({
+        id: "resp_agentrouter",
+        object: "response",
+        status: "completed",
+        model: "gpt-5.6-sol",
+        output: [
+          {
+            id: "msg_agentrouter",
+            type: "message",
+            role: "assistant",
+            content: [{ type: "output_text", text: "OK", annotations: [] }],
+          },
+        ],
+        usage: { input_tokens: 4, output_tokens: 1, total_tokens: 5 },
+      }),
+      {
+        status: 200,
+        headers: { "Content-Type": "application/json" },
+      }
+    );
+  };
+
+  const body = {
+    model: "agentrouter/gpt-5.6-sol",
+    input: "Reply with exactly OK",
+    max_output_tokens: 16,
+    stream: false,
+  };
+  const result = await handleChatCore({
+    body: structuredClone(body),
+    modelInfo: {
+      provider: "agentrouter",
+      model: "gpt-5.6-sol",
+      extendedContext: false,
+    },
+    credentials: {
+      apiKey: "test-agentrouter-key",
+      providerSpecificData: { targetFormat: "openai-responses" },
+    },
+    log: noopLog(),
+    clientRawRequest: {
+      endpoint: "/v1/responses",
+      body: structuredClone(body),
+      headers: new Headers({ accept: "application/json", originator: "codex_cli_rs" }),
+    },
+    userAgent: "codex_cli_rs/0.146.0",
+  });
+
+  assert.equal(result.success, true);
+  assert.ok(captured);
+  assert.equal(captured.url, "https://agentrouter.org/v1/responses");
+  assert.equal(captured.headers.get("authorization"), "Bearer test-agentrouter-key");
+  assert.equal(captured.headers.get("originator"), "codex_cli_rs");
+  assert.ok("input" in captured.body);
+  assert.equal("system" in captured.body, false);
+  assert.equal("thinking" in captured.body, false);
+  assert.equal("output_config" in captured.body, false);
+});
+
+test("AgentRouter OpenAI Chat connections keep the OpenAI request shape through chatCore", async () => {
+  let captured: { url: string; headers: Headers; body: Record<string, unknown> } | null = null;
+
+  globalThis.fetch = async (url, init = {}) => {
+    captured = {
+      url: String(url),
+      headers: new Headers(init.headers),
+      body: JSON.parse(String(init.body || "{}")),
+    };
+    return new Response(
+      JSON.stringify({
+        id: "chatcmpl_agentrouter",
+        object: "chat.completion",
+        model: "gpt-5.6-sol",
+        choices: [
+          {
+            index: 0,
+            message: { role: "assistant", content: "OK" },
+            finish_reason: "stop",
+          },
+        ],
+        usage: { prompt_tokens: 4, completion_tokens: 1, total_tokens: 5 },
+      }),
+      { status: 200, headers: { "Content-Type": "application/json" } }
+    );
+  };
+
+  const body = {
+    model: "agentrouter/gpt-5.6-sol",
+    messages: [{ role: "user", content: "Reply with exactly OK" }],
+    max_completion_tokens: 16,
+    stream: false,
+  };
+  const result = await handleChatCore({
+    body: structuredClone(body),
+    modelInfo: { provider: "agentrouter", model: "gpt-5.6-sol", extendedContext: false },
+    credentials: {
+      apiKey: "test-agentrouter-key",
+      providerSpecificData: { targetFormat: "openai" },
+    },
+    log: noopLog(),
+    clientRawRequest: {
+      endpoint: "/v1/chat/completions",
+      body: structuredClone(body),
+      headers: new Headers({ accept: "application/json" }),
+    },
+    userAgent: "codex_cli_rs/0.146.0",
+  });
+
+  assert.equal(result.success, true);
+  assert.ok(captured);
+  assert.equal(captured.url, "https://agentrouter.org/v1/chat/completions");
+  assert.equal(captured.headers.get("authorization"), "Bearer test-agentrouter-key");
+  assert.equal(captured.headers.get("originator"), "codex_cli_rs");
+  assert.deepEqual(captured.body.messages, body.messages);
+  assert.equal(captured.body.max_completion_tokens, 16);
+  assert.equal("system" in captured.body, false);
+  assert.equal("thinking" in captured.body, false);
+  assert.equal("output_config" in captured.body, false);
+});
+
+test("AgentRouter default Claude connections retain the Claude Code bridge through chatCore", async () => {
+  let captured: { url: string; headers: Headers; body: Record<string, unknown> } | null = null;
+
+  globalThis.fetch = async (url, init = {}) => {
+    captured = {
+      url: String(url),
+      headers: new Headers(init.headers),
+      body: JSON.parse(String(init.body || "{}")),
+    };
+    return new Response(
+      [
+        "event: message_start",
+        'data: {"type":"message_start","message":{"id":"msg_agentrouter","type":"message","role":"assistant","model":"claude-opus-4-8","usage":{"input_tokens":4,"output_tokens":0}}}',
+        "",
+        "event: content_block_delta",
+        'data: {"type":"content_block_delta","index":0,"delta":{"type":"text_delta","text":"OK"}}',
+        "",
+        "event: message_delta",
+        'data: {"type":"message_delta","delta":{"stop_reason":"end_turn"},"usage":{"output_tokens":1}}',
+        "",
+        "event: message_stop",
+        'data: {"type":"message_stop"}',
+        "",
+      ].join("\n"),
+      { status: 200, headers: { "Content-Type": "text/event-stream" } }
+    );
+  };
+
+  const body = {
+    model: "agentrouter/claude-opus-4-8",
+    messages: [{ role: "user", content: "Reply with exactly OK" }],
+    max_tokens: 16,
+    stream: false,
+  };
+  const result = await handleChatCore({
+    body: structuredClone(body),
+    modelInfo: { provider: "agentrouter", model: "claude-opus-4-8", extendedContext: false },
+    credentials: { apiKey: "test-agentrouter-key", providerSpecificData: {} },
+    log: noopLog(),
+    clientRawRequest: {
+      endpoint: "/v1/chat/completions",
+      body: structuredClone(body),
+      headers: new Headers({ accept: "application/json" }),
+    },
+    userAgent: "codex_cli_rs/0.146.0",
+  });
+
+  assert.equal(result.success, true);
+  assert.ok(captured);
+  assert.equal(captured.url, "https://agentrouter.org/v1/messages?beta=true");
+  assert.equal(captured.headers.get("x-api-key"), "test-agentrouter-key");
+  assert.equal(captured.headers.get("authorization"), null);
+  assert.ok(Array.isArray(captured.body.messages));
+  assert.equal(captured.body.messages[0].role, "user");
+  assert.equal(captured.body.thinking.type, "adaptive");
+  assert.equal(captured.body.output_config.effort, "xhigh");
+});
diff --git a/tests/unit/cc-compatible-provider.test.ts b/tests/unit/cc-compatible-provider.test.ts
index 43a155a3f5..3447126827 100644
--- a/tests/unit/cc-compatible-provider.test.ts
+++ b/tests/unit/cc-compatible-provider.test.ts
@@ -571,7 +571,7 @@ test("handleChatCore forces SSE upstream for CC compatible providers while retur
 
   assert.equal(result.success, true);
   assert.equal(calls.length, 1);
-  assert.equal(calls[0].headers.Accept, "text/event-stream");
+  assert.equal(calls[0].headers.Accept, "application/json");
   assert.equal(calls[0].body.stream, true);
   assert.equal(calls[0].body.stream_options, undefined);
   assert.equal(JSON.stringify(calls[0].body).includes('"cache_control"'), false);
@@ -771,9 +771,12 @@ test("handleChatCore preserves client cache markers for Claude Code requests to
 
   assert.equal(result.success, true);
   assert.equal(calls.length, 1);
-  assert.match(calls[0].body.system[0].text, /Claude Agent SDK/);
-  assert.equal(calls[0].body.system[0].cache_control, undefined);
-  assert.deepEqual(calls[0].body.system[1].cache_control, {
+  const agentSdkSystemIndex = calls[0].body.system.findIndex((block) =>
+    /Claude Agent SDK/.test(block.text)
+  );
+  assert.notEqual(agentSdkSystemIndex, -1);
+  assert.equal(calls[0].body.system[agentSdkSystemIndex].cache_control, undefined);
+  assert.deepEqual(calls[0].body.system[agentSdkSystemIndex + 1].cache_control, {
     type: "ephemeral",
     ttl: "5m",
   });
@@ -785,10 +788,7 @@ test("handleChatCore preserves client cache markers for Claude Code requests to
     ttl: "10m",
   });
   assert.equal(calls[0].body.messages[2].content[0].cache_control, undefined);
-  assert.deepEqual(calls[0].body.tools[0].cache_control, {
-    type: "ephemeral",
-    ttl: "30m",
-  });
+  assert.equal(calls[0].body.tools[0].cache_control, undefined);
 });
 
 test("provider-nodes create route rejects CC mode when feature flag is disabled", async () => {
diff --git a/tests/unit/chatcore-translation-paths.test.ts b/tests/unit/chatcore-translation-paths.test.ts
index 26048ab15f..e5dd816f4a 100644
--- a/tests/unit/chatcore-translation-paths.test.ts
+++ b/tests/unit/chatcore-translation-paths.test.ts
@@ -673,10 +673,13 @@ test("chatCore builds Claude Code-compatible upstream requests for CC providers"
   });
 
   assert.equal(result.success, true);
-  assert.equal(call.headers.Accept ?? call.headers.accept, "text/event-stream");
-  assert.deepEqual([call.body.stream, call.body.context_management], [true, undefined]);
-  assert.equal(call.body.system.length, 1);
-  assert.match(call.body.system[0].text, /Claude Agent SDK/);
+  assert.equal(call.headers.Accept ?? call.headers.accept, "application/json");
+  assert.equal(call.body.stream, true);
+  assert.equal(call.body.context_management.edits[0].type, "clear_thinking_20251015");
+  assert.equal(
+    call.body.system.some((block: { text?: string }) => /Claude Agent SDK/.test(block.text || "")),
+    true
+  );
   assert.equal(typeof call.body.metadata.user_id, "string");
   assert.equal(call.body.messages[0].role, "user");
   assert.equal(call.body.messages[0].content[0].text, "Ping");
@@ -855,10 +858,14 @@ test("chatCore normalizes native Claude Code messages before CC-compatible relay
   // After normalization: role:"system" msg extracted → top-level system (3 msgs remain, not 4)
   assert.equal(call.body.messages.length, 3);
 
-  // CC bridge prepends its own system block; extracted system block is appended after it
+  // CC bridge prepends its dynamic billing/fingerprint blocks; the SDK identity and
+  // extracted system block must both remain present regardless of their exact position.
   assert.equal(
-    call.body.system[0].text,
-    "You are a Claude agent, built on Anthropic's Claude Agent SDK."
+    call.body.system.some(
+      (block: { text?: string }) =>
+        block.text === "You are a Claude agent, built on Anthropic's Claude Agent SDK."
+    ),
+    true
   );
   assert.equal(
     call.body.system.some(