diff --git a/.changeset/legacy-acp-optionid-compat.md b/.changeset/legacy-acp-optionid-compat.md
new file mode 100644
index 000000000..2da8e7b52
--- /dev/null
+++ b/.changeset/legacy-acp-optionid-compat.md
@@ -0,0 +1,6 @@
+---
+"@moonshot-ai/acp-adapter": patch
+"@moonshot-ai/kimi-code": patch
+---
+
+Fix ACP custom client tools being auto-rejected when using legacy Python ACP SDK optionId values (`approve`, `approve_for_session`)
diff --git a/packages/acp-adapter/src/approval.ts b/packages/acp-adapter/src/approval.ts
index 8e183fdae..874116002 100644
--- a/packages/acp-adapter/src/approval.ts
+++ b/packages/acp-adapter/src/approval.ts
@@ -22,6 +22,17 @@ export const APPROVE_ONCE_OPTION_ID = 'approve_once';
 export const APPROVE_ALWAYS_OPTION_ID = 'approve_always';
 export const REJECT_OPTION_ID = 'reject';
 
+/**
+ * Legacy option ids sent by older ACP clients (e.g. Python ACP SDK 0.8.x).
+ * Mapped to the canonical ids so that clients built against the older SDK
+ * continue to work without modification.
+ */
+const LEGACY_OPTION_ID_MAP: Record<string, string> = {
+  approve: APPROVE_ONCE_OPTION_ID,
+  approve_for_session: APPROVE_ALWAYS_OPTION_ID,
+  reject: REJECT_OPTION_ID,
+};
+
 /**
  * Phase 13.2 plan_review optionId namespace. Picked deliberately so the
  * `plan_*` prefix never collides with the canonical `approve_*` /
@@ -151,10 +162,11 @@ export function permissionResponseToApprovalResponse(
   if (response.outcome.outcome === 'cancelled') {
     return { decision: 'cancelled' };
   }
-  const optionId = response.outcome.optionId;
+  const rawOptionId = response.outcome.optionId;
   if (req?.display.kind === 'plan_review') {
-    return mapPlanReviewOptionId(req.display, optionId);
+    return mapPlanReviewOptionId(req.display, rawOptionId);
   }
+  const optionId = LEGACY_OPTION_ID_MAP[rawOptionId] ?? rawOptionId;
   switch (optionId) {
     case APPROVE_ONCE_OPTION_ID:
       return { decision: 'approved' };
@@ -310,7 +322,14 @@ export function attachSelectedLabel(
   ) {
     return approval;
   }
-  const matched = options.find((o) => o.optionId === outcome.optionId);
+  // Normalize legacy ids (Python ACP SDK 0.8.x sends `approve` /
+  // `approve_for_session` / `reject`) to their canonical equivalents
+  // before the lookup. Without this, legacy approvals are correctly
+  // routed by `permissionResponseToApprovalResponse` but drop the
+  // human-readable `selectedLabel` (e.g. "Approve for this session"),
+  // so PermissionResult hooks and approval records lose context.
+  const normalizedOptionId = LEGACY_OPTION_ID_MAP[outcome.optionId] ?? outcome.optionId;
+  const matched = options.find((o) => o.optionId === normalizedOptionId);
   if (!matched) return approval;
   return { ...approval, selectedLabel: matched.name };
 }
diff --git a/packages/acp-adapter/test/approval-display.test.ts b/packages/acp-adapter/test/approval-display.test.ts
index bbedb07e5..cec2ce548 100644
--- a/packages/acp-adapter/test/approval-display.test.ts
+++ b/packages/acp-adapter/test/approval-display.test.ts
@@ -259,6 +259,30 @@ describe('attachSelectedLabel', () => {
     expect(result).toEqual({ decision: 'rejected', selectedLabel: 'Reject' });
   });
 
+  it('attaches "Approve once" when the legacy "approve" optionId is selected', () => {
+    const approval: ApprovalResponse = { decision: 'approved' };
+    const result = attachSelectedLabel(
+      { outcome: { outcome: 'selected', optionId: 'approve' } },
+      approval,
+      options,
+    );
+    expect(result).toEqual({ decision: 'approved', selectedLabel: 'Approve once' });
+  });
+
+  it('attaches "Approve for this session" when the legacy "approve_for_session" optionId is selected', () => {
+    const approval: ApprovalResponse = { decision: 'approved', scope: 'session' };
+    const result = attachSelectedLabel(
+      { outcome: { outcome: 'selected', optionId: 'approve_for_session' } },
+      approval,
+      options,
+    );
+    expect(result).toEqual({
+      decision: 'approved',
+      scope: 'session',
+      selectedLabel: 'Approve for this session',
+    });
+  });
+
   it('returns the input unchanged when the optionId is unknown', () => {
     const approval: ApprovalResponse = { decision: 'rejected' };
     const result = attachSelectedLabel(
diff --git a/packages/acp-adapter/test/approval.test.ts b/packages/acp-adapter/test/approval.test.ts
index 309466697..3a8001d07 100644
--- a/packages/acp-adapter/test/approval.test.ts
+++ b/packages/acp-adapter/test/approval.test.ts
@@ -175,6 +175,21 @@ describe('permissionResponseToApprovalResponse', () => {
     expect(result).toEqual({ decision: 'rejected' });
   });
 
+  it('maps legacy "approve" → { decision: approved } (Python ACP SDK compat)', () => {
+    const result = permissionResponseToApprovalResponse(undefined, {
+      outcome: { outcome: 'selected', optionId: 'approve' },
+    });
+    expect(result).toEqual({ decision: 'approved' });
+    expect(result.scope).toBeUndefined();
+  });
+
+  it('maps legacy "approve_for_session" → { decision: approved, scope: session } (Python ACP SDK compat)', () => {
+    const result = permissionResponseToApprovalResponse(undefined, {
+      outcome: { outcome: 'selected', optionId: 'approve_for_session' },
+    });
+    expect(result).toEqual({ decision: 'approved', scope: 'session' });
+  });
+
   it('defensively maps an unknown optionId to { decision: rejected }', () => {
     const result = permissionResponseToApprovalResponse(undefined, {
       outcome: { outcome: 'selected', optionId: 'unknown_option_id' },