diff --git a/extensions/cohere/index.test.ts b/extensions/cohere/index.test.ts
index b3e773ae6e8f..e20eef4268a6 100644
--- a/extensions/cohere/index.test.ts
+++ b/extensions/cohere/index.test.ts
@@ -32,11 +32,14 @@ function captureCoherePayload(context: Context): Record<string, unknown> {
       { maxTokens: 2048 } as never,
     );
     options?.onPayload?.(payload, model);
-    captured = payload;
     return {} as ReturnType<StreamFn>;
   };
 
-  void createCohereCompletionsWrapper(baseStreamFn)(requireCohereModel(), context, {});
+  void createCohereCompletionsWrapper(baseStreamFn)(requireCohereModel(), context, {
+    onPayload: (payload) => {
+      captured = payload as Record<string, unknown>;
+    },
+  });
   if (!captured) {
     throw new Error("Cohere payload was not captured");
   }
@@ -104,5 +107,11 @@ describe("Cohere provider plugin", () => {
     expect(params).not.toHaveProperty("store");
     expect(params).not.toHaveProperty("stream_options");
     expect(params).not.toHaveProperty("tool_choice");
+    expect(params.messages).toEqual(
+      expect.arrayContaining([expect.objectContaining({ role: "developer", content: "system" })]),
+    );
+    expect(params.messages).not.toEqual(
+      expect.arrayContaining([expect.objectContaining({ role: "system", content: "system" })]),
+    );
   });
 });
diff --git a/extensions/cohere/stream.ts b/extensions/cohere/stream.ts
index 032800a8437a..5038cc7acc7a 100644
--- a/extensions/cohere/stream.ts
+++ b/extensions/cohere/stream.ts
@@ -1,17 +1,26 @@
 import type { ProviderWrapStreamFnContext } from "openclaw/plugin-sdk/plugin-entry";
 import { createPayloadPatchStreamWrapper } from "openclaw/plugin-sdk/provider-stream-shared";
 
+function patchCoherePayload(payload: Record<string, unknown>): void {
+  // Cohere's Compatibility API uses developer, not system, for instructions.
+  if (Array.isArray(payload.messages)) {
+    payload.messages = payload.messages.map((message) =>
+      message &&
+      typeof message === "object" &&
+      (message as Record<string, unknown>).role === "system"
+        ? { ...(message as Record<string, unknown>), role: "developer" }
+        : message,
+    );
+  }
+
+  // Cohere lets tool-capable models choose a tool when tool_choice is omitted.
+  delete payload.tool_choice;
+}
+
 export function createCohereCompletionsWrapper(
   baseStreamFn: ProviderWrapStreamFnContext["streamFn"],
 ): ProviderWrapStreamFnContext["streamFn"] {
-  return createPayloadPatchStreamWrapper(
-    baseStreamFn,
-    ({ payload }) => {
-      // Cohere lets tool-capable models choose a tool when tool_choice is omitted.
-      delete payload.tool_choice;
-    },
-    {
-      shouldPatch: ({ model }) => model.provider === "cohere" && model.api === "openai-completions",
-    },
+  return createPayloadPatchStreamWrapper(baseStreamFn, ({ payload }) =>
+    patchCoherePayload(payload),
   );
 }