diff --git a/open-sse/executors/azure.js b/open-sse/executors/azure.js
index 574cda22f9..6e871d2135 100644
--- a/open-sse/executors/azure.js
+++ b/open-sse/executors/azure.js
@@ -51,7 +51,27 @@ export class AzureExecutor extends DefaultExecutor {
     return headers;
   }
 
+  // Azure OpenAI reasoning-model deployments (gpt-5*, o1-/o3-/o4- series) reject
+  // the legacy `max_tokens` param with a 400 "Unsupported parameter" error and
+  // require `max_completion_tokens` instead. Same rule the "github" executor
+  // already applies for Copilot-hosted reasoning models.
+  requiresMaxCompletionTokens(model) {
+    return /gpt-5|o[134]-/i.test(model);
+  }
+
   transformRequest(model, body, stream, credentials) {
-    return body;
+    if (!this.requiresMaxCompletionTokens(model) || !body || typeof body !== "object" || body.max_tokens === undefined) {
+      return body;
+    }
+
+    const transformed = { ...body };
+    // An explicit max_completion_tokens from the caller wins; max_tokens is
+    // only used as a fallback. Either way max_tokens must be stripped, or
+    // Azure 400s on it regardless of max_completion_tokens being present.
+    if (transformed.max_completion_tokens === undefined) {
+      transformed.max_completion_tokens = transformed.max_tokens;
+    }
+    delete transformed.max_tokens;
+    return transformed;
   }
 }
diff --git a/tests/unit/azure-executor.test.js b/tests/unit/azure-executor.test.js
new file mode 100644
index 0000000000..2e57648d50
--- /dev/null
+++ b/tests/unit/azure-executor.test.js
@@ -0,0 +1,78 @@
+import { describe, it, expect } from "vitest";
+import { AzureExecutor } from "../../open-sse/executors/azure.js";
+import { getExecutor, hasSpecializedExecutor } from "../../open-sse/executors/index.js";
+
+describe("AzureExecutor registry", () => {
+  it("is registered on executor map", () => {
+    expect(hasSpecializedExecutor("azure")).toBe(true);
+    expect(getExecutor("azure")).toBeInstanceOf(AzureExecutor);
+  });
+});
+
+describe("AzureExecutor.requiresMaxCompletionTokens", () => {
+  const executor = new AzureExecutor();
+
+  it("matches gpt-5 family deployments", () => {
+    expect(executor.requiresMaxCompletionTokens("gpt-5.6-luna")).toBe(true);
+    expect(executor.requiresMaxCompletionTokens("gpt-5-mini")).toBe(true);
+    expect(executor.requiresMaxCompletionTokens("GPT-5.6-SOL")).toBe(true);
+  });
+
+  it("matches o1/o3/o4 reasoning deployments", () => {
+    expect(executor.requiresMaxCompletionTokens("o1-preview")).toBe(true);
+    expect(executor.requiresMaxCompletionTokens("o3-mini")).toBe(true);
+    expect(executor.requiresMaxCompletionTokens("o4-mini")).toBe(true);
+  });
+
+  it("does not match non-reasoning deployments", () => {
+    expect(executor.requiresMaxCompletionTokens("gpt-4o")).toBe(false);
+    expect(executor.requiresMaxCompletionTokens("gpt-4.1-nano")).toBe(false);
+    expect(executor.requiresMaxCompletionTokens("o2-something")).toBe(false);
+  });
+});
+
+describe("AzureExecutor.transformRequest", () => {
+  const executor = new AzureExecutor();
+
+  it("renames max_tokens to max_completion_tokens for reasoning deployments", () => {
+    const body = { messages: [{ role: "user", content: "hi" }], max_tokens: 50 };
+    const out = executor.transformRequest("gpt-5.6-luna", body, true, {});
+
+    expect(out.max_tokens).toBeUndefined();
+    expect(out.max_completion_tokens).toBe(50);
+    // original body must not be mutated
+    expect(body.max_tokens).toBe(50);
+  });
+
+  it("leaves max_tokens untouched for non-reasoning deployments", () => {
+    const body = { messages: [{ role: "user", content: "hi" }], max_tokens: 50 };
+    const out = executor.transformRequest("gpt-4o", body, true, {});
+
+    expect(out).toBe(body);
+    expect(out.max_tokens).toBe(50);
+    expect(out.max_completion_tokens).toBeUndefined();
+  });
+
+  it("is a no-op when max_tokens is absent", () => {
+    const body = { messages: [{ role: "user", content: "hi" }] };
+    const out = executor.transformRequest("gpt-5.6-luna", body, true, {});
+
+    expect(out).toBe(body);
+    expect(out.max_completion_tokens).toBeUndefined();
+  });
+
+  it("keeps an explicit max_completion_tokens and still deletes max_tokens", () => {
+    const body = {
+      messages: [{ role: "user", content: "hi" }],
+      max_tokens: 50,
+      max_completion_tokens: 200,
+    };
+    const out = executor.transformRequest("gpt-5.6-luna", body, true, {});
+
+    expect(out.max_completion_tokens).toBe(200);
+    expect(out.max_tokens).toBeUndefined();
+    // original body must not be mutated
+    expect(body.max_completion_tokens).toBe(200);
+    expect(body.max_tokens).toBe(50);
+  });
+});