diff --git a/CHANGELOG.md b/CHANGELOG.md
index 2e0f34140e..2dd4bf4ea0 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -20,6 +20,8 @@
 
 ### 🐛 Bug Fixes
 
+- **fix(executors):** inject the `reasoning_content` echo for the native **Moonshot Kimi** provider. Kimi (executor `default`) is a thinking-mode upstream that 400s with "reasoning_content must be passed back" when a prior assistant turn lacks it; the placeholder injection was only wired into the OpenCode meta-provider, so direct multi-turn Kimi conversations failed. Scoped to `kimi` (gateway-served models matching the thinking-model name pattern are unaffected). Regression guard: `tests/unit/kimi-native-reasoning-injected-1480.test.ts`. (thanks @2220258345)
+
 - **fix(live-ws):** the Live Dashboard WebSocket server now **rejects on bind failure** (e.g. `EADDRINUSE` when the API bridge already holds the port) instead of letting the error surface as an unhandled `error` event that crash-loops the process — the `error` listener is attached to `wss` (not `server`) and releases the EventBus subscription on a failed start ([#6324](https://github.com/diegosouzapw/OmniRoute/issues/6324)). Regression guard: `tests/unit/live-ws-eaddrinuse-6324.test.ts`. (thanks @vinayakkulkarni)
 - **fix(dashboard):** the Home provider-topology widget now trusts the live provider-metrics snapshot — it uses `topology.errorProvider` and live `activeRequests` directly instead of re-deriving state from a stale `lastErrorAt` or applying a frontend timeout filter, so the topology reflects real-time provider health. Regression guard: `tests/unit/home-provider-topology-live-state.test.ts`. (thanks @xz-dev)
 - **fix(sse):** strip zero-width markers from streamed **tool-call arguments** — a follow-up to [#5857](https://github.com/diegosouzapw/OmniRoute/pull/5857). That PR removed injected zero-width joiners (U+200D) from streamed assistant text/reasoning but deliberately left tool-call argument JSON byte-exact. The request-side obfuscation (`open-sse/services/claudeCodeObfuscation.ts`) injects ZWJ into agent words — including the temp path inside the Bash tool description — and Claude models copy that verbatim into generated commands, which are delivered as tool-call arguments rather than assistant text. As a result the ZWJ survived and corrupted code blocks (e.g. a temp path rendered with an invisible joiner). Now `open-sse/handlers/responseSanitizer.ts` strips zero-width code points from tool-call argument strings at every emit site (OpenAI non-stream/stream chat `tool_calls` + legacy `function_call`, native Responses `function_call` items, the OpenAI→Responses conversion, and the native Responses streaming `response.function_call_arguments.delta/.done` events). Only zero-width code points are removed; JSON structure and all other bytes stay identical (no parse/restringify), so normal arguments remain byte-exact. Regression guard: 6 new cases in `tests/unit/response-sanitizer.test.ts` (suite 50/50).
diff --git a/open-sse/executors/default.ts b/open-sse/executors/default.ts
index afabd75645..4b844f4c76 100644
--- a/open-sse/executors/default.ts
+++ b/open-sse/executors/default.ts
@@ -17,6 +17,10 @@ import {
 import { isOfficialAnthropicBaseUrl } from "../utils/anthropicHost.ts";
 import { applyProviderRequestDefaults } from "../services/providerRequestDefaults.ts";
 import { stripUnsupportedParams } from "../translator/paramSupport.ts";
+import {
+  injectReasoningContentForThinkingModel,
+  isThinkingMessageModel,
+} from "../utils/reasoningContentInjector.ts";
 import {
   detectFormat,
   getOpenAICompatibleType,
@@ -695,6 +699,23 @@ export class DefaultExecutor extends BaseExecutor {
       this.ensureThinkingBudget(withDefaults as Record<string, unknown>, model);
     }
 
+    // 9router#1480: the native Moonshot `kimi` provider (executor "default")
+    // is a thinking-mode upstream that 400s with "reasoning_content must be
+    // passed back" when a prior assistant turn lacks it. OpencodeExecutor
+    // already injects a placeholder for OpenCode-routed thinking models; the
+    // direct kimi connection hit neither injection path. Scope to `kimi` so
+    // gateway-served models that merely match the thinking-model name pattern
+    // (and may reject an extra field) are unaffected.
+    if (this.provider === "kimi") {
+      const outboundModel =
+        typeof (withDefaults as Record<string, unknown>)?.model === "string"
+          ? ((withDefaults as Record<string, unknown>).model as string)
+          : model;
+      if (isThinkingMessageModel(outboundModel)) {
+        withDefaults = injectReasoningContentForThinkingModel(withDefaults);
+      }
+    }
+
     return withDefaults;
   }
 
diff --git a/tests/unit/kimi-native-reasoning-injected-1480.test.ts b/tests/unit/kimi-native-reasoning-injected-1480.test.ts
new file mode 100644
index 0000000000..1654a8185f
--- /dev/null
+++ b/tests/unit/kimi-native-reasoning-injected-1480.test.ts
@@ -0,0 +1,65 @@
+import test from "node:test";
+import assert from "node:assert/strict";
+
+import { DefaultExecutor } from "../../open-sse/executors/default.ts";
+
+/**
+ * Regression guard for upstream 9router#1480.
+ *
+ * The native Moonshot `kimi` provider (executor "default") is a thinking-mode
+ * upstream that returns 400 "reasoning_content must be passed back" when a prior
+ * assistant turn in the history lacks `reasoning_content`. OpencodeExecutor
+ * already injects a placeholder for OpenCode-routed thinking models, but the
+ * direct kimi connection went through DefaultExecutor, which did not — so
+ * multi-turn kimi conversations 400'd. The injection must fire for `kimi`, and
+ * must NOT fire for unrelated providers that merely serve a matching model name.
+ */
+
+const STREAM = true;
+const CREDENTIALS = { apiKey: "k" } as Record<string, unknown>;
+
+function multiTurnBody(model: string) {
+  return {
+    model,
+    stream: STREAM,
+    messages: [
+      { role: "user", content: "hi" },
+      { role: "assistant", content: "previous answer" }, // no reasoning_content
+      { role: "user", content: "follow up" },
+    ],
+  };
+}
+
+test("DefaultExecutor(kimi) injects reasoning_content on assistant turns that lack it", () => {
+  const out = new DefaultExecutor("kimi").transformRequest(
+    "kimi-k2.6",
+    multiTurnBody("kimi-k2.6"),
+    STREAM,
+    CREDENTIALS
+  ) as Record<string, unknown>;
+  const messages = out.messages as Array<Record<string, unknown>>;
+  const assistant = messages.find((m) => m.role === "assistant") as Record<string, unknown>;
+  assert.equal(
+    typeof assistant.reasoning_content === "string" &&
+      (assistant.reasoning_content as string).length > 0,
+    true,
+    "kimi assistant message must carry a non-empty reasoning_content placeholder"
+  );
+});
+
+test("DefaultExecutor(openai) does NOT inject reasoning_content (scoped to kimi)", () => {
+  // A non-kimi provider must not gain the injection even for a thinking-ish name.
+  const out = new DefaultExecutor("openai").transformRequest(
+    "kimi-k2.6",
+    multiTurnBody("kimi-k2.6"),
+    STREAM,
+    CREDENTIALS
+  ) as Record<string, unknown>;
+  const messages = out.messages as Array<Record<string, unknown>>;
+  const assistant = messages.find((m) => m.role === "assistant") as Record<string, unknown>;
+  assert.equal(
+    Object.prototype.hasOwnProperty.call(assistant, "reasoning_content"),
+    false,
+    "non-kimi providers must not be given a reasoning_content placeholder"
+  );
+});