diff --git a/src/hooks/anthropic-effort/hook.ts b/src/hooks/anthropic-effort/hook.ts
index 31b18c7e6..6d4cc965c 100644
--- a/src/hooks/anthropic-effort/hook.ts
+++ b/src/hooks/anthropic-effort/hook.ts
@@ -65,6 +65,7 @@ export function createAnthropicEffortHook() {
       if (isEffortUnsupportedModel(model.modelID)) return
       if (message.variant !== "max") return
       if (!isClaudeProvider(model.providerID, model.modelID)) return
+      if (model.providerID === "github-copilot") return
       if (shouldSkipForInternalAgent(agent?.name)) return
       if (output.options.effort !== undefined) return
 
diff --git a/src/hooks/anthropic-effort/index.test.ts b/src/hooks/anthropic-effort/index.test.ts
index 5ca923cd2..cea012eb9 100644
--- a/src/hooks/anthropic-effort/index.test.ts
+++ b/src/hooks/anthropic-effort/index.test.ts
@@ -148,6 +148,22 @@ describe("createAnthropicEffortHook", () => {
       expect(output.options.effort).toBeUndefined()
     })
 
+    it("#given github-copilot + claude model #then effort NOT injected", async () => {
+      // given
+      const hook = createAnthropicEffortHook()
+      const { input, output } = createMockParams({
+        providerID: "github-copilot",
+        modelID: "claude-opus-4-6",
+      })
+
+      // when
+      await hook["chat.params"](input, output)
+
+      // then
+      expect(output.options.effort).toBeUndefined()
+      expect(input.message.variant).toBe("max")
+    })
+
     describe("#given haiku models (effort unsupported)", () => {
       const haikuModels = [
         "claude-haiku-4-5",