diff --git a/lib/deprecations.js b/lib/deprecations.js
new file mode 100644
index 00000000..ae9a3119
--- /dev/null
+++ b/lib/deprecations.js
@@ -0,0 +1,56 @@
+'use strict';
+
+const { promises: fs } = require('fs');
+const path = require('path');
+const replace = require('replace-in-file');
+
+const newDeprecationPattern =
+/<\s*a id="DEP0([X]+[0-9]*)+"[^>]*><\s*\/\s*a>/g;
+
+async function getUnmarkedDeprecations() {
+  const deprecationFilePath = path.resolve('doc', 'api', 'deprecations.md');
+  const deprecationFile = await fs.readFile(deprecationFilePath, 'utf8');
+
+  const unmarkedDeprecations = [
+    ...deprecationFile.matchAll(newDeprecationPattern)
+  ].map(m => m[1]);
+
+  return unmarkedDeprecations;
+}
+
+async function updateDeprecations(unmarkedDeprecations) {
+  const deprecationPattern =
+    /<\s*a id="DEP0([0-9]{3})+"[^>]*><\s*\/\s*a>/g;
+
+  const deprecationFilePath = path.resolve('doc', 'api', 'deprecations.md');
+  const deprecationFile = await fs.readFile(deprecationFilePath, 'utf8');
+
+  const deprecationNumbers = [
+    ...deprecationFile.matchAll(deprecationPattern)
+  ].map(m => m[1]).reverse();
+
+  // Pull highest deprecation number off the list and increment from there.
+  let depNumber = parseInt(deprecationNumbers[0]) + 1;
+
+  // Loop through each new unmarked deprecation number and replace instances.
+  for (const unmarked of unmarkedDeprecations) {
+    await replace({
+      files: [
+        'doc/api/*.md',
+        'lib/**/*.js',
+        'src/**/*.{h,cc}',
+        'test/**/*.js'
+      ],
+      ignore: 'test/common/README.md',
+      from: new RegExp(`DEP0${unmarked}`, 'g'),
+      to: `DEP0${depNumber}`
+    });
+
+    depNumber++;
+  }
+}
+
+module.exports = {
+  updateDeprecations,
+  getUnmarkedDeprecations
+};
diff --git a/lib/landing_session.js b/lib/landing_session.js
index fc45c5ec..718b5c3a 100644
--- a/lib/landing_session.js
+++ b/lib/landing_session.js
@@ -1,14 +1,16 @@
 'use strict';
 
 const path = require('path');
+const {
+  getUnmarkedDeprecations,
+  updateDeprecations
+} = require('./deprecations');
 
 const {
   runAsync, runSync, forceRunAsync
 } = require('./run');
 const Session = require('./session');
-const {
-  shortSha
-} = require('./utils');
+const { shortSha } = require('./utils');
 
 const isWindows = process.platform === 'win32';
 
@@ -84,6 +86,21 @@ class LandingSession extends Session {
         process.exit(1);
       }
     }
+
+    // Check for and maybe assign any unmarked deprecations in the codebase.
+    const unmarkedDeprecations = await getUnmarkedDeprecations();
+    const unmarkedDepCount = unmarkedDeprecations.length;
+    if (unmarkedDepCount > 0) {
+      cli.startSpinner('Assigning deprecation numbers to DEPOXXX items');
+
+      // Update items then stage files and amend the last commit.
+      await updateDeprecations(unmarkedDeprecations);
+      await runAsync('git', ['add', 'doc', 'lib', 'src', 'test']);
+      await runAsync('git', ['commit', '--amend', '--no-edit']);
+
+      cli.stopSpinner(`Updated ${unmarkedDepCount} DEPOXXX items in codebase`);
+    }
+
     cli.ok('Patches applied');
     return patch;
   }
diff --git a/lib/prepare_release.js b/lib/prepare_release.js
index 9a5b12c9..e664d81d 100644
--- a/lib/prepare_release.js
+++ b/lib/prepare_release.js
@@ -1,13 +1,17 @@
 'use strict';
 
 const path = require('path');
-const fs = require('fs').promises;
+const { promises: fs } = require('fs');
 const semver = require('semver');
 const replace = require('replace-in-file');
 
 const { getMergedConfig } = require('./config');
 const { runAsync, runSync } = require('./run');
 const { writeJson, readJson } = require('./file');
+const {
+  getUnmarkedDeprecations,
+  updateDeprecations
+} = require('./deprecations');
 
 const isWindows = process.platform === 'win32';
 
@@ -113,6 +117,26 @@ class ReleasePreparation {
     await this.updateREPLACEMEs();
     cli.stopSpinner('Updated REPLACEME items in docs');
 
+    // Check for and maybe assign any unmarked deprecations in the codebase.
+    const unmarkedDeprecations = await getUnmarkedDeprecations();
+    const unmarkedDepCount = unmarkedDeprecations.length;
+    if (unmarkedDepCount > 0) {
+      if (unmarkedDepCount === 1) {
+        cli.startSpinner(
+          'Assigning deprecation number to DEPOXXX item');
+        await updateDeprecations(unmarkedDeprecations);
+        cli.stopSpinner('Assigned deprecation numbers to DEPOXXX items');
+      } else {
+        cli.warn(
+          'More than one unmarked DEPOXXX item - manual resolution required.');
+
+        await cli.prompt(
+          `Finished updating ${unmarkedDepCount} unmarked DEPOXXX items?`,
+          { defaultAnswer: false });
+        cli.stopSpinner(`Finished updating ${unmarkedDepCount} DEPOXXX items`);
+      }
+    }
+
     // Fetch date to use in release commit & changelogs.
     const todayDate = new Date().toISOString().split('T')[0];
     this.date = await cli.prompt('Enter release date in YYYY-MM-DD format:',