diff --git a/apps/studio/lib/ai/prompts.ts b/apps/studio/lib/ai/prompts.ts
index b0c637c4d1f80..f1ababc6acb93 100644
--- a/apps/studio/lib/ai/prompts.ts
+++ b/apps/studio/lib/ai/prompts.ts
@@ -766,7 +766,7 @@ export const NOTEBOOKS_PROMPT = `
 - Use \`update_notebook\` to edit an existing notebook — insert, replace, delete, or move cells — instead of recreating it from scratch.
 - Use \`execute_sql\` for a single ad-hoc question with no need to persist it.
 - When the request clearly calls for a notebook, call \`create_notebook\` or \`update_notebook\` directly; both tools handle user approval.
-- \`update_notebook\` re-fetches the notebook right before applying edits, so the latest save always wins — it cannot detect edits made by someone else in between.
+- \`update_notebook\` requires \`expected_updated_at\`, the \`updated_at\` you got from \`get_notebook\`. If the notebook changed since, the call is rejected — call \`get_notebook\` again and reissue \`update_notebook\` against the current content.
 - When describing an existing notebook, report each query cell's configuration that changes what it returns — a log cell's time range, a database cell's row limit — and don't count markdown cells as queries.
 `
 
diff --git a/apps/studio/lib/ai/tools/mock-tools.test.ts b/apps/studio/lib/ai/tools/mock-tools.test.ts
index a9b808b703f21..bbd437a5add38 100644
--- a/apps/studio/lib/ai/tools/mock-tools.test.ts
+++ b/apps/studio/lib/ai/tools/mock-tools.test.ts
@@ -182,6 +182,7 @@ describe('ai/tools/mock-tools getMockTools', () => {
       const result = await mockTools.update_notebook.execute(
         {
           id: AUTH_HEALTH_NOTEBOOK_ID,
+          expected_updated_at: before.updated_at,
           operations: [
             {
               _tag: 'insert_cell',
@@ -218,10 +219,16 @@ describe('ai/tools/mock-tools getMockTools', () => {
       if (!mockTools.get_notebook.execute) throw new Error('execute is undefined')
       if (!mockTools.update_notebook.execute) throw new Error('execute is undefined')
 
+      const before = await mockTools.get_notebook.execute(
+        { id: EDGE_FUNCTION_NOTEBOOK_ID },
+        { toolCallId: 'test', messages: [] }
+      )
+
       await expect(
         mockTools.update_notebook.execute(
           {
             id: EDGE_FUNCTION_NOTEBOOK_ID,
+            expected_updated_at: before.updated_at,
             operations: [{ _tag: 'delete_cell', cell_id: 'does-not-exist' }],
           },
           { toolCallId: 'test', messages: [] }
diff --git a/apps/studio/lib/ai/tools/mock-tools.ts b/apps/studio/lib/ai/tools/mock-tools.ts
index a5fc459e8142c..0c06860d0f712 100644
--- a/apps/studio/lib/ai/tools/mock-tools.ts
+++ b/apps/studio/lib/ai/tools/mock-tools.ts
@@ -451,6 +451,7 @@ function createMockNotebookTools(store: MockNotebookStore) {
           name: notebook.name,
           description: notebook.description,
           visibility: notebook.visibility,
+          updated_at: notebook.updated_at,
           cells: notebook.content.cells,
         }
       },
@@ -484,8 +485,14 @@ function createMockNotebookTools(store: MockNotebookStore) {
       ...update_notebook,
       // Same reasoning as create_notebook's override above.
       needsApproval: false,
+      // expected_updated_at is validated by the real inputSchema (spread above) but not
+      // checked here: the in-memory store has no concurrent writers for the eval harness
+      // to race against.
       execute: async (
-        { id, operations }: { id: string; operations: NotebookOperation[] },
+        {
+          id,
+          operations,
+        }: { id: string; expected_updated_at: string; operations: NotebookOperation[] },
         _options: ToolCallOptions
       ) => {
         const notebook = store.get(id)
diff --git a/apps/studio/lib/ai/tools/notebook-tools.test.ts b/apps/studio/lib/ai/tools/notebook-tools.test.ts
index c6889a74a0677..3185c8315a994 100644
--- a/apps/studio/lib/ai/tools/notebook-tools.test.ts
+++ b/apps/studio/lib/ai/tools/notebook-tools.test.ts
@@ -202,6 +202,7 @@ describe('ai/tools/notebook-tools', () => {
         name: 'Signup funnel',
         description: undefined,
         visibility: 'project',
+        updated_at: '2026-01-01T00:00:00.000Z',
         cells: [
           { _tag: 'markdown_cell', id: 'cell-1', text: '# Signup funnel' },
           {
@@ -399,6 +400,7 @@ describe('ai/tools/notebook-tools', () => {
       const result = await tools.update_notebook.execute(
         {
           id: 'notebook-1',
+          expected_updated_at: '2026-01-01T00:00:00.000Z',
           operations: [
             { _tag: 'delete_cell', cell_id: 'cell-3' },
             {
@@ -432,10 +434,32 @@ describe('ai/tools/notebook-tools', () => {
 
       await expect(
         tools.update_notebook.execute(
-          { id: 'notebook-1', operations: [{ _tag: 'delete_cell', cell_id: 'missing-cell' }] },
+          {
+            id: 'notebook-1',
+            expected_updated_at: '2026-01-01T00:00:00.000Z',
+            operations: [{ _tag: 'delete_cell', cell_id: 'missing-cell' }],
+          },
           { toolCallId: 'test', messages: [] }
         )
       ).rejects.toThrow('No cell with id "missing-cell"')
     })
+
+    it('should throw instead of PUTting when the notebook changed since expected_updated_at', async () => {
+      mockGetNotebook()
+
+      const tools = getNotebookTools({ projectRef: 'test-project' })
+      if (!tools.update_notebook.execute) throw new Error('execute is undefined')
+
+      await expect(
+        tools.update_notebook.execute(
+          {
+            id: 'notebook-1',
+            expected_updated_at: '2025-12-31T00:00:00.000Z',
+            operations: [{ _tag: 'delete_cell', cell_id: 'cell-3' }],
+          },
+          { toolCallId: 'test', messages: [] }
+        )
+      ).rejects.toThrow(/changed since expected_updated_at/)
+    })
   })
 })
diff --git a/apps/studio/lib/ai/tools/notebook-tools.ts b/apps/studio/lib/ai/tools/notebook-tools.ts
index c5e95f3d077a4..a0d62f1adc800 100644
--- a/apps/studio/lib/ai/tools/notebook-tools.ts
+++ b/apps/studio/lib/ai/tools/notebook-tools.ts
@@ -85,6 +85,7 @@ export const getNotebookTools = (ctx: NotebookToolsContext = {}) => {
           name: notebook.name,
           description: notebook.description,
           visibility: notebook.visibility,
+          updated_at: notebook.updated_at,
           // Inlined rather than a shared helper: this discards the `unchecked_sql` brand for
           // display purposes only — the result is returned to the agent, never written back.
           cells: notebook.content.cells.map((cell) => {
@@ -149,17 +150,28 @@ export const getNotebookTools = (ctx: NotebookToolsContext = {}) => {
     }),
     update_notebook: tool({
       description:
-        'Asks the user to apply an ordered list of cell operations (insert, replace, delete, move) to an existing notebook. Requires user approval before updating. Re-fetches the notebook right before applying the operations; concurrent edits are last-write-wins.',
+        'Asks the user to apply an ordered list of cell operations (insert, replace, delete, move) to an existing notebook. Requires user approval before updating. Re-fetches the notebook right before applying the operations and rejects the update if it changed since expected_updated_at.',
       inputSchema: z.object({
         id: z.string().describe('The id of the notebook to update.'),
+        expected_updated_at: z
+          .string()
+          .describe(
+            'The `updated_at` you received from `get_notebook`. The update is rejected if the notebook changed since.'
+          ),
         operations: notebookOperationsSchema.describe(
           'An ordered list of operations to apply to the notebook, addressing existing cells by id.'
         ),
       }),
       needsApproval: true,
-      execute: async ({ id, operations }) => {
+      execute: async ({ id, expected_updated_at, operations }) => {
         const notebook = await getNotebook({ projectRef, id }, undefined, authHeaders)
 
+        if (notebook.updated_at !== expected_updated_at) {
+          throw new Error(
+            `Notebook "${id}" changed since expected_updated_at (${expected_updated_at}); it is now ${notebook.updated_at}. Call get_notebook again and reissue update_notebook against the current content.`
+          )
+        }
+
         // Inlined rather than a shared helper, right beside this tool's own
         // `needsApproval: true`: this discards each cell's `unchecked_sql` brand so
         // applyNotebookOperations can splice cells as plain data. The result is never