diff --git a/open-sse/executors/codex.js b/open-sse/executors/codex.js
index eaac4bf651b..db3b634f5ad 100644
--- a/open-sse/executors/codex.js
+++ b/open-sse/executors/codex.js
@@ -414,17 +414,28 @@ export class CodexExecutor extends BaseExecutor {
     }
 
     // Priority: explicit reasoning.effort > reasoning_effort param > model suffix > default (medium)
-    if (!body.reasoning) {
-      const effort = body.reasoning_effort || modelEffort || 'low';
-      body.reasoning = { effort, summary: "auto" };
-    } else if (!body.reasoning.summary) {
-      body.reasoning.summary = "auto";
+    if (!body.reasoning || typeof body.reasoning !== 'object' || Array.isArray(body.reasoning)) {
+      const effort = body.reasoning_effort || modelEffort || 'medium';
+      body.reasoning = { effort, summary: 'auto' };
+    } else {
+      if (!body.reasoning.effort) {
+        body.reasoning.effort = body.reasoning_effort || modelEffort || 'medium';
+      }
+      if (!body.reasoning.summary) {
+        body.reasoning.summary = 'auto';
+      }
     }
     delete body.reasoning_effort;
 
     // Include reasoning encrypted content (required by Codex backend for reasoning models)
+    const include = Array.isArray(body.include) ? body.include : [];
     if (body.reasoning && body.reasoning.effort && body.reasoning.effort !== 'none') {
-      body.include = ["reasoning.encrypted_content"];
+      body.include = include.includes("reasoning.encrypted_content")
+        ? include
+        : [...include, "reasoning.encrypted_content"];
+    } else if (include.length > 0) {
+      body.include = include.filter(item => item !== "reasoning.encrypted_content");
+      if (body.include.length === 0) delete body.include;
     }
 
     // Remove unsupported parameters for Codex API
diff --git a/open-sse/translator/request/openai-responses.js b/open-sse/translator/request/openai-responses.js
index 2c329d6ec7c..e216398557d 100644
--- a/open-sse/translator/request/openai-responses.js
+++ b/open-sse/translator/request/openai-responses.js
@@ -309,6 +309,7 @@ export function openaiToOpenAIResponsesRequest(model, body, stream, credentials)
   if (body.temperature !== undefined) result.temperature = body.temperature;
   if (body.max_tokens !== undefined) result.max_tokens = body.max_tokens;
   if (body.top_p !== undefined) result.top_p = body.top_p;
+  if (body.reasoning_effort !== undefined) result.reasoning_effort = body.reasoning_effort;
 
   return result;
 }
diff --git a/tests/unit/codex-request-transform.test.js b/tests/unit/codex-request-transform.test.js
new file mode 100644
index 00000000000..4e24d3b57e6
--- /dev/null
+++ b/tests/unit/codex-request-transform.test.js
@@ -0,0 +1,154 @@
+import { describe, expect, it } from "vitest";
+import { CodexExecutor } from "../../open-sse/executors/codex.js";
+import { openaiToOpenAIResponsesRequest } from "../../open-sse/translator/request/openai-responses.js";
+
+function makeBody(overrides = {}) {
+  return {
+    input: [{ type: "message", role: "user", content: [{ type: "input_text", text: "hi" }] }],
+    ...overrides,
+  };
+}
+
+describe("CodexExecutor request transform", () => {
+  it("defaults base Codex models to medium effort", () => {
+    const executor = new CodexExecutor();
+    const out = executor.transformRequest("gpt-5.3-codex", makeBody({ model: "gpt-5.3-codex" }), true, {});
+
+    expect(out.model).toBe("gpt-5.3-codex");
+    expect(out.reasoning).toEqual({ effort: "medium", summary: "auto" });
+    expect(out.include).toEqual(["reasoning.encrypted_content"]);
+    expect(out.reasoning_effort).toBeUndefined();
+  });
+
+  it("uses model effort suffix and strips suffix before upstream call", () => {
+    const executor = new CodexExecutor();
+    const out = executor.transformRequest("gpt-5.3-codex-high", makeBody({ model: "gpt-5.3-codex-high" }), true, {});
+
+    expect(out.model).toBe("gpt-5.3-codex");
+    expect(out.reasoning).toEqual({ effort: "high", summary: "auto" });
+  });
+
+  it("keeps explicit reasoning.effort over model suffix", () => {
+    const executor = new CodexExecutor();
+    const out = executor.transformRequest(
+      "gpt-5.3-codex-high",
+      makeBody({ model: "gpt-5.3-codex-high", reasoning: { effort: "low" } }),
+      true,
+      {},
+    );
+
+    expect(out.model).toBe("gpt-5.3-codex");
+    expect(out.reasoning).toEqual({ effort: "low", summary: "auto" });
+  });
+
+  it("applies reasoning_effort when reasoning object lacks effort", () => {
+    const executor = new CodexExecutor();
+    const out = executor.transformRequest(
+      "gpt-5.3-codex",
+      makeBody({ model: "gpt-5.3-codex", reasoning: { summary: "detailed" }, reasoning_effort: "xhigh" }),
+      true,
+      {},
+    );
+
+    expect(out.reasoning).toEqual({ effort: "xhigh", summary: "detailed" });
+    expect(out.reasoning_effort).toBeUndefined();
+  });
+
+  it("preserves Chat Completions reasoning_effort through OpenAI Responses translation", () => {
+    const translated = openaiToOpenAIResponsesRequest(
+      "gpt-5.3-codex",
+      {
+        model: "gpt-5.3-codex",
+        messages: [{ role: "user", content: "hi" }],
+        reasoning_effort: "high",
+      },
+      true,
+      null,
+    );
+
+    const executor = new CodexExecutor();
+    const out = executor.transformRequest("gpt-5.3-codex", translated, true, {});
+
+    expect(out.reasoning).toEqual({ effort: "high", summary: "auto" });
+    expect(out.reasoning_effort).toBeUndefined();
+  });
+
+  it("does not request encrypted reasoning content when effort is none", () => {
+    const executor = new CodexExecutor();
+    const out = executor.transformRequest("gpt-5.3-codex-none", makeBody({ model: "gpt-5.3-codex-none" }), true, {});
+
+    expect(out.model).toBe("gpt-5.3-codex");
+    expect(out.reasoning).toEqual({ effort: "none", summary: "auto" });
+    expect(out.include).toBeUndefined();
+  });
+
+  it("removes encrypted reasoning include when effort is none", () => {
+    const executor = new CodexExecutor();
+    const out = executor.transformRequest(
+      "gpt-5.3-codex",
+      makeBody({
+        model: "gpt-5.3-codex",
+        reasoning_effort: "none",
+        include: ["reasoning.encrypted_content"],
+      }),
+      true,
+      {},
+    );
+
+    expect(out.reasoning).toEqual({ effort: "none", summary: "auto" });
+    expect(out.include).toBeUndefined();
+  });
+
+  it("preserves existing include values when adding encrypted reasoning content", () => {
+    const executor = new CodexExecutor();
+    const out = executor.transformRequest(
+      "gpt-5.3-codex",
+      makeBody({
+        model: "gpt-5.3-codex",
+        include: ["web_search_call.action.sources"],
+      }),
+      true,
+      {},
+    );
+
+    expect(out.include).toEqual(["web_search_call.action.sources", "reasoning.encrypted_content"]);
+  });
+
+  it("maps review aliases before effort suffix parsing", () => {
+    const executor = new CodexExecutor();
+    const out = executor.transformRequest(
+      "gpt-5.3-codex-high-review",
+      makeBody({ model: "gpt-5.3-codex-high-review" }),
+      true,
+      {},
+    );
+
+    expect(out.model).toBe("gpt-5.3-codex");
+    expect(out.reasoning).toEqual({ effort: "high", summary: "auto" });
+  });
+
+  it("strips parameters Codex backend rejects", () => {
+    const executor = new CodexExecutor();
+    const out = executor.transformRequest(
+      "gpt-5.3-codex",
+      makeBody({
+        model: "gpt-5.3-codex",
+        max_tokens: 100,
+        max_completion_tokens: 100,
+        max_output_tokens: 100,
+        temperature: 0.2,
+        stream_options: { include_usage: true },
+        previous_response_id: "resp_abc",
+      }),
+      true,
+      {},
+    );
+
+    expect(out.max_tokens).toBeUndefined();
+    expect(out.max_completion_tokens).toBeUndefined();
+    expect(out.max_output_tokens).toBeUndefined();
+    expect(out.temperature).toBeUndefined();
+    expect(out.stream_options).toBeUndefined();
+    expect(out.previous_response_id).toBeUndefined();
+  });
+});