diff --git a/apis/api-journeys-modern/src/lib/google/sheets.ts b/apis/api-journeys-modern/src/lib/google/sheets.ts
index a39e8f8f4cf..d9eda06ea5f 100644
--- a/apis/api-journeys-modern/src/lib/google/sheets.ts
+++ b/apis/api-journeys-modern/src/lib/google/sheets.ts
@@ -267,6 +267,12 @@ export async function readValues({
   return values
 }
 
+// Escape a sheet title for use in A1 notation ranges.
+// Per Google Sheets: wrap in single quotes, doubling any internal single quotes.
+export function escapeSheetName(name: string): string {
+  return `'${name.replace(/'/g, "''")}'`
+}
+
 // Convert a 0-based column index to A1 column letters
 export function columnIndexToA1(colIndexZeroBased: number): string {
   let n = colIndexZeroBased + 1
diff --git a/apis/api-journeys-modern/src/workers/googleSheetsSync/service/backfill.spec.ts b/apis/api-journeys-modern/src/workers/googleSheetsSync/service/backfill.spec.ts
new file mode 100644
index 00000000000..b57f122d64a
--- /dev/null
+++ b/apis/api-journeys-modern/src/workers/googleSheetsSync/service/backfill.spec.ts
@@ -0,0 +1,173 @@
+import { Job } from 'bullmq'
+import { Logger } from 'pino'
+
+import { prismaMock } from '../../../../test/prismaMock'
+import { getIntegrationGoogleAccessToken } from '../../../lib/google/googleAuth'
+import {
+  clearSheet,
+  ensureSheet,
+  readValues,
+  writeValues
+} from '../../../lib/google/sheets'
+import { GoogleSheetsSyncBackfillJobData } from '../queue'
+
+import { backfillService } from './backfill'
+
+jest.mock('../../../lib/google/googleAuth', () => ({
+  getIntegrationGoogleAccessToken: jest.fn()
+}))
+
+jest.mock('../../../lib/google/sheets', () => {
+  const actual = jest.requireActual('../../../lib/google/sheets')
+  return {
+    ...actual,
+    clearSheet: jest.fn(),
+    ensureSheet: jest.fn(),
+    readValues: jest.fn(),
+    writeValues: jest.fn()
+  }
+})
+
+const mockGetIntegrationGoogleAccessToken =
+  getIntegrationGoogleAccessToken as jest.MockedFunction<
+    typeof getIntegrationGoogleAccessToken
+  >
+const mockEnsureSheet = ensureSheet as jest.MockedFunction<typeof ensureSheet>
+const mockReadValues = readValues as jest.MockedFunction<typeof readValues>
+const mockClearSheet = clearSheet as jest.MockedFunction<typeof clearSheet>
+const mockWriteValues = writeValues as jest.MockedFunction<typeof writeValues>
+
+const backfillJob: Job<GoogleSheetsSyncBackfillJobData> = {
+  name: 'google-sheets-sync-backfill',
+  data: {
+    type: 'backfill',
+    journeyId: 'journey-id',
+    teamId: 'team-id',
+    syncId: 'sync-id',
+    spreadsheetId: 'spreadsheet-id',
+    sheetName: 'Sheet1',
+    timezone: 'UTC',
+    integrationId: 'integration-id'
+  }
+} as unknown as Job<GoogleSheetsSyncBackfillJobData>
+
+describe('backfillService', () => {
+  let logger: Logger
+
+  beforeEach(() => {
+    jest.clearAllMocks()
+    logger = {
+      info: jest.fn(),
+      warn: jest.fn(),
+      error: jest.fn()
+    } as unknown as Logger
+
+    prismaMock.googleSheetsSync.findFirst.mockResolvedValue({
+      id: 'sync-id'
+    } as any)
+    prismaMock.journey.findUnique.mockResolvedValue({
+      id: 'journey-id',
+      blocks: []
+    } as any)
+    prismaMock.event.findMany.mockResolvedValue([] as any)
+    prismaMock.journeyVisitor.findMany.mockResolvedValue([] as any)
+
+    mockGetIntegrationGoogleAccessToken.mockResolvedValue({
+      accessToken: 'access-token',
+      accountEmail: 'example@example.com'
+    })
+    mockEnsureSheet.mockResolvedValue(undefined)
+  })
+
+  it('skips clear/write when sheet content is unchanged', async () => {
+    mockReadValues.mockResolvedValue([['Visitor ID', 'Date']])
+
+    await backfillService(backfillJob, logger)
+
+    expect(mockReadValues).toHaveBeenCalledWith({
+      accessToken: 'access-token',
+      spreadsheetId: 'spreadsheet-id',
+      range: "'Sheet1'!A:B"
+    })
+    expect(mockClearSheet).not.toHaveBeenCalled()
+    expect(mockWriteValues).not.toHaveBeenCalled()
+  })
+
+  it('clears and rewrites when sheet content changed', async () => {
+    mockReadValues.mockResolvedValue([['Visitor ID', 'Date (Old)']])
+
+    await backfillService(backfillJob, logger)
+
+    expect(mockClearSheet).toHaveBeenCalledWith({
+      accessToken: 'access-token',
+      spreadsheetId: 'spreadsheet-id',
+      sheetTitle: 'Sheet1'
+    })
+    expect(mockWriteValues).toHaveBeenCalledWith({
+      accessToken: 'access-token',
+      spreadsheetId: 'spreadsheet-id',
+      sheetTitle: 'Sheet1',
+      values: [['Visitor ID', 'Date']],
+      append: false
+    })
+  })
+
+  it('clears and rewrites when existing sheet has more rows than new data', async () => {
+    mockReadValues.mockResolvedValue([
+      ['Visitor ID', 'Date'],
+      ['visitor-1', '2026-01-01']
+    ])
+
+    await backfillService(backfillJob, logger)
+
+    expect(mockClearSheet).toHaveBeenCalled()
+    expect(mockWriteValues).toHaveBeenCalled()
+  })
+
+  it('clears and rewrites when existing sheet is empty', async () => {
+    mockReadValues.mockResolvedValue([])
+
+    await backfillService(backfillJob, logger)
+
+    expect(mockClearSheet).toHaveBeenCalled()
+    expect(mockWriteValues).toHaveBeenCalled()
+  })
+
+  it('falls through to write when readValues fails', async () => {
+    mockReadValues.mockRejectedValue(new Error('API rate limit exceeded'))
+
+    await backfillService(backfillJob, logger)
+
+    expect(logger.warn).toHaveBeenCalledWith(
+      expect.objectContaining({ err: expect.any(Error) }),
+      'Failed to read existing sheet values, proceeding with full write'
+    )
+    expect(mockClearSheet).toHaveBeenCalled()
+    expect(mockWriteValues).toHaveBeenCalled()
+  })
+
+  it('skips backfill when sync is not found', async () => {
+    prismaMock.googleSheetsSync.findFirst.mockResolvedValue(null)
+
+    await backfillService(backfillJob, logger)
+
+    expect(logger.warn).toHaveBeenCalledWith(
+      expect.objectContaining({ syncId: 'sync-id' }),
+      'Sync not found or deleted, skipping backfill'
+    )
+    expect(mockEnsureSheet).not.toHaveBeenCalled()
+    expect(mockReadValues).not.toHaveBeenCalled()
+  })
+
+  it('skips backfill when journey is not found', async () => {
+    prismaMock.journey.findUnique.mockResolvedValue(null)
+
+    await backfillService(backfillJob, logger)
+
+    expect(logger.warn).toHaveBeenCalledWith(
+      expect.objectContaining({ journeyId: 'journey-id' }),
+      'Journey not found, skipping backfill'
+    )
+    expect(mockEnsureSheet).not.toHaveBeenCalled()
+  })
+})
diff --git a/apis/api-journeys-modern/src/workers/googleSheetsSync/service/backfill.ts b/apis/api-journeys-modern/src/workers/googleSheetsSync/service/backfill.ts
index 184239155a1..13e260614de 100644
--- a/apis/api-journeys-modern/src/workers/googleSheetsSync/service/backfill.ts
+++ b/apis/api-journeys-modern/src/workers/googleSheetsSync/service/backfill.ts
@@ -6,7 +6,10 @@ import { Prisma, prisma } from '@core/prisma/journeys/client'
 import { getIntegrationGoogleAccessToken } from '../../../lib/google/googleAuth'
 import {
   clearSheet,
+  columnIndexToA1,
   ensureSheet,
+  escapeSheetName,
+  readValues,
   writeValues
 } from '../../../lib/google/sheets'
 import { computeConnectedBlockIds } from '../../../schema/journeyVisitor/export/connectivity'
@@ -44,6 +47,30 @@ interface JourneyVisitorExportRow {
   [key: string]: string
 }
 
+function isSheetContentUnchanged({
+  nextValues,
+  existingValues,
+  writeWidth
+}: {
+  nextValues: (string | null)[][]
+  existingValues: (string | null)[][]
+  writeWidth: number
+}): boolean {
+  if (existingValues.length !== nextValues.length) return false
+
+  return nextValues.every((nextRow, rowIndex) => {
+    const existingRow = existingValues[rowIndex] ?? []
+
+    for (let colIndex = 0; colIndex < writeWidth; colIndex++) {
+      const nextCell = String(nextRow[colIndex] ?? '')
+      const existingCell = String(existingRow[colIndex] ?? '')
+      if (nextCell !== existingCell) return false
+    }
+
+    return true
+  })
+}
+
 async function* getJourneyVisitors(
   journeyId: string,
   eventWhere: Prisma.EventWhereInput,
@@ -281,9 +308,6 @@ export async function backfillService(
   // Ensure sheet exists
   await ensureSheet({ accessToken, spreadsheetId, sheetTitle: sheetName })
 
-  // Clear existing data
-  await clearSheet({ accessToken, spreadsheetId, sheetTitle: sheetName })
-
   // Build data rows
   const sanitizedHeaderRow = headerRow.map((cell) =>
     sanitizeGoogleSheetsCell(cell)
@@ -303,14 +327,46 @@ export async function backfillService(
     values.push(aligned)
   }
 
-  // Write all data at once
-  await writeValues({
-    accessToken,
-    spreadsheetId,
-    sheetTitle: sheetName,
-    values,
-    append: false
-  })
+  const writeWidth = finalHeader.length
+  const lastColumnA1 = columnIndexToA1(writeWidth - 1)
+  const escapedName = escapeSheetName(sheetName)
+  const fullRange = `${escapedName}!A:${lastColumnA1}`
+
+  let existingValues: (string | null)[][] = []
+  let readFailed = false
+  try {
+    existingValues = await readValues({
+      accessToken,
+      spreadsheetId,
+      range: fullRange
+    })
+  } catch (err) {
+    readFailed = true
+    logger?.warn(
+      { err, range: fullRange },
+      'Failed to read existing sheet values, proceeding with full write'
+    )
+  }
+
+  const contentUnchanged =
+    !readFailed &&
+    isSheetContentUnchanged({
+      nextValues: values,
+      existingValues,
+      writeWidth
+    })
+
+  if (!contentUnchanged) {
+    await clearSheet({ accessToken, spreadsheetId, sheetTitle: sheetName })
+
+    await writeValues({
+      accessToken,
+      spreadsheetId,
+      sheetTitle: sheetName,
+      values,
+      append: false
+    })
+  }
 
   // Update exportOrder on blocks that don't have it set yet.
   // This ensures columns maintain their positions for future syncs.