diff --git a/.changeset/savings-storage-at-rest-detach-from-savings-report.md b/.changeset/savings-storage-at-rest-detach-from-savings-report.md
new file mode 100644
index 0000000..a3ae843
--- /dev/null
+++ b/.changeset/savings-storage-at-rest-detach-from-savings-report.md
@@ -0,0 +1,9 @@
+---
+'@colony/core': patch
+---
+
+Stop attributing the storage-at-rest compression claim to live `savings_report` calls
+
+The `Storage at rest (per observation)` reference row used to map to `['savings_report']`. Live `savings_report` output is structured JSON (~3.5k tokens per call) where the caveman compressor preserves technical tokens byte-for-byte, so the live comparison projected the row's 1k-token baseline against ~3.5k actual tokens and reported negative savings (e.g. `-155%`).
+
+The row stays in the static reference — caveman compression really does shrink prose observations on disk — but it is now a structural claim about the storage layer rather than a per-call cost, so `mcp_operations` is empty. `savings_report` calls now show up under `unmatched_operations` instead of inflating the row.
diff --git a/apps/mcp-server/test/task-threads.test.ts b/apps/mcp-server/test/task-threads.test.ts
index ce54598..987ce54 100644
--- a/apps/mcp-server/test/task-threads.test.ts
+++ b/apps/mcp-server/test/task-threads.test.ts
@@ -1554,7 +1554,9 @@ describe('task_claim_file — protected-branch guard', () => {
       arguments: { task_id: thread.task_id, session_id: 'S1', file_path: '/repo/src/index.ts' },
     });
     expect(res.isError).toBe(true);
-    const body = JSON.parse((res.content as Array<{ type: string; text: string }>)[0]?.text ?? '{}');
+    const body = JSON.parse(
+      (res.content as Array<{ type: string; text: string }>)[0]?.text ?? '{}',
+    );
     expect(body.code).toBe(TASK_THREAD_ERROR_CODES.PROTECTED_BRANCH_CLAIM_REJECTED);
     // No claim row written.
     expect(guardedStore.storage.getClaim(thread.task_id, '/repo/src/index.ts')).toBeFalsy();
@@ -1572,7 +1574,9 @@ describe('task_claim_file — protected-branch guard', () => {
       arguments: { task_id: thread.task_id, session_id: 'S2', file_path: '/repo/src/index.ts' },
     });
     expect(res.isError).toBeFalsy();
-    const body = JSON.parse((res.content as Array<{ type: string; text: string }>)[0]?.text ?? '{}');
+    const body = JSON.parse(
+      (res.content as Array<{ type: string; text: string }>)[0]?.text ?? '{}',
+    );
     expect(body.claim_status).toBe('claimed');
   });
 });
diff --git a/packages/core/src/savings-reference.ts b/packages/core/src/savings-reference.ts
index 73f7594..32f474b 100644
--- a/packages/core/src/savings-reference.ts
+++ b/packages/core/src/savings-reference.ts
@@ -228,8 +228,8 @@ export const SAVINGS_REFERENCE_ROWS: ReadonlyArray<SavingsReferenceRow> = [
     1,
     1_000,
     300,
-    'caveman compression preserves technical tokens byte-for-byte',
-    ['savings_report'],
+    'caveman compression keeps prose observations small on disk; this is a structural claim about the storage layer, not the cost of any single MCP call, so no live operation is mapped (savings_report itself emits structured JSON that is mostly preserved-as-is technical tokens, which made it a misleading proxy)',
+    [],
   ),
   row(
     'Plan publication & goal anchoring',
diff --git a/packages/core/test/savings-reference.test.ts b/packages/core/test/savings-reference.test.ts
index 2841874..e95e784 100644
--- a/packages/core/test/savings-reference.test.ts
+++ b/packages/core/test/savings-reference.test.ts
@@ -1,5 +1,9 @@
 import { describe, expect, it } from 'vitest';
-import { savingsLiveComparison, savingsLiveComparisonCost } from '../src/savings-reference.js';
+import {
+  SAVINGS_REFERENCE_ROWS,
+  savingsLiveComparison,
+  savingsLiveComparisonCost,
+} from '../src/savings-reference.js';
 
 describe('savings reference receipts', () => {
   it('estimates USD saved from matched live mcp_metrics costs', () => {
@@ -49,4 +53,33 @@ describe('savings reference receipts', () => {
       saved_cost_usd: 0.097,
     });
   });
+
+  it('does not attribute structured-output savings_report calls to the at-rest compression row', () => {
+    // Regression: the "Storage at rest (per observation)" row used to map to
+    // ['savings_report'], which produced negative live savings because
+    // savings_report emits ~3.5k tokens of structured JSON per call against a
+    // 1k baseline. The row stays in the static reference (compression is real
+    // for prose observations) but no live MCP operation should be mapped to
+    // it.
+    const storageAtRestRow = SAVINGS_REFERENCE_ROWS.find(
+      (r) => r.operation === 'Storage at rest (per observation)',
+    );
+    expect(storageAtRestRow).toBeDefined();
+    expect(storageAtRestRow?.mcp_operations).toEqual([]);
+
+    const comparison = savingsLiveComparison([
+      {
+        operation: 'savings_report',
+        calls: 2,
+        total_tokens: 5100,
+        last_ts: 1,
+      },
+    ]);
+    expect(
+      comparison.rows.find((r) => r.operation === 'Storage at rest (per observation)'),
+    ).toBeUndefined();
+    expect(
+      comparison.unmatched_operations.find((u) => u.operation === 'savings_report'),
+    ).toMatchObject({ operation: 'savings_report', calls: 2, colony_tokens: 5100 });
+  });
 });