diff --git a/src/cliproxy/config/generator.ts b/src/cliproxy/config/generator.ts
index 61b565a5..fc79958e 100644
--- a/src/cliproxy/config/generator.ts
+++ b/src/cliproxy/config/generator.ts
@@ -36,8 +36,10 @@ export const CCS_CONTROL_PANEL_SECRET = 'ccs';
  * v12: Removed denylisted Antigravity Claude 4.5 aliases
  * v13: Removed aggressive Gemini alias expansion to reduce model list noise in Control Panel
  * v14: Added Gemini 3.1 Flash Antigravity aliases for upcoming rollout compatibility
+ * v15: Prune stale generated Antigravity Gemini preview aliases during regeneration
+ * v16: Narrow stale Gemini alias cleanup to broad multi-version guessed ranges
  */
-export const CLIPROXY_CONFIG_VERSION = 14;
+export const CLIPROXY_CONFIG_VERSION = 16;
 
 interface OAuthModelAliasEntry {
   name: string;
@@ -45,6 +47,11 @@ interface OAuthModelAliasEntry {
   fork?: boolean;
 }
 
+interface PreservedAntigravityAliasesResult {
+  yaml: string;
+  prunedLegacyAliasCount: number;
+}
+
 const DEPRECATED_ANTIGRAVITY_ALIAS_PREFIX = 'gemini-claude-';
 const UPSTREAM_CLAUDE_ALIAS_PREFIX = 'claude-';
 const DEPRECATED_ANTIGRAVITY_SONNET_46_THINKING_REGEX = /^claude-sonnet-4(?:[.-])6-thinking$/i;
@@ -69,6 +76,17 @@ const DEFAULT_ANTIGRAVITY_ALIASES: OAuthModelAliasEntry[] = [
   { name: 'claude-opus-4-6-thinking', alias: 'claude-opus-4-6-thinking', fork: true },
 ];
 
+const BUILT_IN_GEMINI_ALIAS_NAMES = new Set(
+  DEFAULT_ANTIGRAVITY_ALIASES.filter((entry) => entry.alias.startsWith('gemini-3')).map(
+    (entry) => entry.name
+  )
+);
+const MIN_STALE_GUESSED_GEMINI_MINOR_VERSIONS = 2;
+const MIN_STALE_HIGH_ONLY_GEMINI_MINOR_VERSIONS = 3;
+const MIN_STALE_GUESSED_GEMINI_AVERAGE_VARIANTS_PER_MINOR = 2;
+const LEGACY_GEMINI_STALE_ALIAS_MIGRATION_VERSION = 16;
+const MAX_LEGACY_MANUAL_GEMINI_MINOR_VERSION = 2;
+
 /**
  * Get provider configuration
  * Model mappings are loaded from config/base-{provider}.settings.json
@@ -148,6 +166,10 @@ function addAliasEntry(
   entries.push(normalized);
 }
 
+function buildAntigravityAliasKey(entry: Pick<OAuthModelAliasEntry, 'name' | 'alias'>): string {
+  return `${sanitizeYamlScalar(entry.name)}\u0000${normalizeAntigravityAlias(entry.alias)}`;
+}
+
 function parseExistingAntigravityAliases(existingAliases: string): OAuthModelAliasEntry[] {
   const entries: OAuthModelAliasEntry[] = [];
   const lines = existingAliases.replace(/\r\n/g, '\n').split('\n');
@@ -204,6 +226,16 @@ function parseExistingAntigravityAliases(existingAliases: string): OAuthModelAli
   return entries;
 }
 
+function getConfigVersionFromContent(content: string): number | null {
+  const versionMatch = content.match(/CCS v(\d+)/);
+  if (!versionMatch) {
+    return null;
+  }
+
+  const parsedVersion = Number.parseInt(versionMatch[1], 10);
+  return Number.isNaN(parsedVersion) ? null : parsedVersion;
+}
+
 function toDottedGeminiVersionAlias(alias: string): string | null {
   const match = alias.match(/^(gemini-\d+)-(\d+)(-.+)$/);
   if (!match) return null;
@@ -267,6 +299,184 @@ function getCompatibilityAliases(entries: OAuthModelAliasEntry[]): OAuthModelAli
   return compatibilityAliases;
 }
 
+function buildGeneratedAntigravityAliases(): OAuthModelAliasEntry[] {
+  const generatedAliases: OAuthModelAliasEntry[] = [];
+  const generatedAliasIndex = new Map<string, number>();
+
+  for (const alias of DEFAULT_ANTIGRAVITY_ALIASES) {
+    addAliasEntry(generatedAliases, generatedAliasIndex, alias);
+  }
+
+  for (const alias of getCompatibilityAliases(generatedAliases)) {
+    addAliasEntry(generatedAliases, generatedAliasIndex, alias);
+  }
+
+  return generatedAliases;
+}
+
+const GENERATED_ANTIGRAVITY_ALIASES = buildGeneratedAntigravityAliases();
+const GENERATED_ANTIGRAVITY_ALIAS_MAP = new Map(
+  GENERATED_ANTIGRAVITY_ALIASES.map((entry) => [buildAntigravityAliasKey(entry), entry] as const)
+);
+
+function serializeAntigravityAliases(entries: OAuthModelAliasEntry[]): string {
+  if (entries.length === 0) {
+    return '';
+  }
+
+  const lines = ['  antigravity:'];
+  for (const entry of entries) {
+    lines.push(`    - name: ${entry.name}`);
+    lines.push(`      alias: ${entry.alias}`);
+    if (entry.fork) {
+      lines.push('      fork: true');
+    }
+  }
+
+  return lines.join('\n');
+}
+
+function getLegacyGeneratedGeminiPreviewInfo(
+  entry: OAuthModelAliasEntry
+): { nameKey: string; minorVersion: string } | null {
+  if (!BUILT_IN_GEMINI_ALIAS_NAMES.has(entry.name)) {
+    return null;
+  }
+
+  const normalizedAlias = normalizeAntigravityAlias(entry.alias).toLowerCase();
+  if (!normalizedAlias.startsWith('gemini-3') || !normalizedAlias.includes('-preview')) {
+    return null;
+  }
+
+  const aliasWithoutCustomtools = normalizedAlias.endsWith('-customtools')
+    ? normalizedAlias.slice(0, -'-customtools'.length)
+    : normalizedAlias;
+  const canonicalAlias =
+    toDottedGeminiVersionAlias(aliasWithoutCustomtools) ?? aliasWithoutCustomtools;
+  const minorVersionMatch = canonicalAlias.match(/^gemini-3\.(\d+)(-.+-preview)$/);
+  if (!minorVersionMatch) {
+    return null;
+  }
+
+  return {
+    nameKey: sanitizeYamlScalar(entry.name),
+    minorVersion: minorVersionMatch[1],
+  };
+}
+
+function buildLegacyGeneratedGeminiAliasPruneSet(
+  parsedEntries: OAuthModelAliasEntry[]
+): Set<string> {
+  const aliasKeysByNameAndMinor = new Map<string, Map<string, string[]>>();
+
+  for (const entry of parsedEntries) {
+    if (entry.fork) {
+      continue;
+    }
+
+    const aliasKey = buildAntigravityAliasKey(entry);
+    if (GENERATED_ANTIGRAVITY_ALIAS_MAP.has(aliasKey)) {
+      continue;
+    }
+
+    const previewInfo = getLegacyGeneratedGeminiPreviewInfo(entry);
+    if (!previewInfo) {
+      continue;
+    }
+
+    const aliasKeysByMinor = aliasKeysByNameAndMinor.get(previewInfo.nameKey) ?? new Map();
+    const aliasKeys = aliasKeysByMinor.get(previewInfo.minorVersion) ?? [];
+    aliasKeys.push(aliasKey);
+    aliasKeysByMinor.set(previewInfo.minorVersion, aliasKeys);
+    aliasKeysByNameAndMinor.set(previewInfo.nameKey, aliasKeysByMinor);
+  }
+
+  const staleAliasKeys = new Set<string>();
+
+  for (const aliasKeysByMinor of aliasKeysByNameAndMinor.values()) {
+    const sortedMinorVersions = [...aliasKeysByMinor.keys()].sort((left, right) => {
+      return Number(left) - Number(right);
+    });
+    const totalAliasCount = sortedMinorVersions.reduce((total, minorVersion) => {
+      return total + (aliasKeysByMinor.get(minorVersion)?.length ?? 0);
+    }, 0);
+    const preservedMinorVersion =
+      Number(sortedMinorVersions[0]) <= MAX_LEGACY_MANUAL_GEMINI_MINOR_VERSION
+        ? sortedMinorVersions[0]
+        : null;
+    const minimumMinorVersionsToPrune = preservedMinorVersion
+      ? MIN_STALE_GUESSED_GEMINI_MINOR_VERSIONS
+      : MIN_STALE_HIGH_ONLY_GEMINI_MINOR_VERSIONS;
+    if (sortedMinorVersions.length < minimumMinorVersionsToPrune) {
+      continue;
+    }
+    if (
+      totalAliasCount <
+      sortedMinorVersions.length * MIN_STALE_GUESSED_GEMINI_AVERAGE_VARIANTS_PER_MINOR
+    ) {
+      continue;
+    }
+
+    for (const minorVersion of sortedMinorVersions) {
+      if (minorVersion === preservedMinorVersion) {
+        continue;
+      }
+
+      const aliasKeys = aliasKeysByMinor.get(minorVersion) ?? [];
+      for (const aliasKey of aliasKeys) {
+        staleAliasKeys.add(aliasKey);
+      }
+    }
+  }
+
+  return staleAliasKeys;
+}
+
+function extractPreservedAntigravityAliases(
+  existingAliases: string,
+  options?: { enableLegacyGeminiStaleCleanup?: boolean }
+): PreservedAntigravityAliasesResult {
+  if (!existingAliases.trim()) {
+    return { yaml: '', prunedLegacyAliasCount: 0 };
+  }
+
+  const parsedEntries = parseExistingAntigravityAliases(existingAliases);
+  const staleAliasKeys = options?.enableLegacyGeminiStaleCleanup
+    ? buildLegacyGeneratedGeminiAliasPruneSet(parsedEntries)
+    : new Set<string>();
+
+  const preservedEntries = parsedEntries.filter((entry) => {
+    const aliasKey = buildAntigravityAliasKey(entry);
+    const generatedEntry = GENERATED_ANTIGRAVITY_ALIAS_MAP.get(aliasKey);
+
+    if (generatedEntry) {
+      return Boolean(entry.fork) && !generatedEntry.fork;
+    }
+
+    if (entry.fork) {
+      return true;
+    }
+
+    return !staleAliasKeys.has(aliasKey);
+  });
+
+  return {
+    yaml: serializeAntigravityAliases(preservedEntries),
+    prunedLegacyAliasCount: parsedEntries.filter((entry) =>
+      staleAliasKeys.has(buildAntigravityAliasKey(entry))
+    ).length,
+  };
+}
+
+function writeLegacyGeminiAliasCleanupBackup(configPath: string, existingContent: string): void {
+  const backupPath = `${configPath}.pre-v16-gemini-alias-cleanup.bak`;
+  if (fs.existsSync(backupPath)) {
+    return;
+  }
+
+  fs.writeFileSync(backupPath, existingContent, { mode: 0o600 });
+}
+
 /**
  * Generate oauth-model-alias YAML section.
  * Merges default Antigravity aliases with any user-added custom aliases.
@@ -543,8 +753,20 @@ export function regenerateConfig(port: number = CLIPROXY_DEFAULT_PORT): string {
       // Preserve claude-api-key section (managed via dashboard/API)
       claudeApiKeySection = extractYamlSection(content, 'claude-api-key');
 
-      // Preserve existing oauth-model-alias user customizations
-      existingAliases = extractYamlSection(content, 'oauth-model-alias');
+      // Preserve user customizations while pruning legacy generated Gemini preview noise.
+      const existingConfigVersion = getConfigVersionFromContent(content);
+      const preservedAliases = extractPreservedAntigravityAliases(
+        extractYamlSection(content, 'oauth-model-alias'),
+        {
+          enableLegacyGeminiStaleCleanup:
+            existingConfigVersion === null ||
+            existingConfigVersion < LEGACY_GEMINI_STALE_ALIAS_MIGRATION_VERSION,
+        }
+      );
+      existingAliases = preservedAliases.yaml;
+      if (preservedAliases.prunedLegacyAliasCount > 0) {
+        writeLegacyGeminiAliasCleanupBackup(configPath, content);
+      }
     } catch {
       // Use defaults if reading fails
     }
@@ -583,12 +805,10 @@ export function configNeedsRegeneration(): boolean {
     const content = fs.readFileSync(configPath, 'utf-8');
 
     // Check for version marker
-    const versionMatch = content.match(/CCS v(\d+)/);
-    if (!versionMatch) {
+    const configVersion = getConfigVersionFromContent(content);
+    if (configVersion === null) {
       return true; // No version marker = old config
     }
-
-    const configVersion = parseInt(versionMatch[1], 10);
     return configVersion < CLIPROXY_CONFIG_VERSION;
   } catch {
     return true; // Error reading = regenerate
diff --git a/tests/unit/cliproxy/config-generator.test.js b/tests/unit/cliproxy/config-generator.test.js
index 4445c807..0e55d717 100644
--- a/tests/unit/cliproxy/config-generator.test.js
+++ b/tests/unit/cliproxy/config-generator.test.js
@@ -753,6 +753,433 @@ oauth-model-alias:
       );
     });
 
+    it('drops stale multi-version Gemini preview ranges while preserving true custom aliases', () => {
+      const cliproxyDir = path.join(testDir, '.ccs', 'cliproxy');
+      fs.mkdirSync(cliproxyDir, { recursive: true });
+      const guessedMinors = ['3', '4', '5', '6'];
+      const buildGuessedRange = (name, family) =>
+        guessedMinors
+          .flatMap((minor) => [
+            `    - name: ${name}`,
+            `      alias: gemini-3.${minor}-${family}-preview`,
+            `    - name: ${name}`,
+            `      alias: gemini-3.${minor}-${family}-preview-customtools`,
+            `    - name: ${name}`,
+            `      alias: gemini-3-${minor}-${family}-preview`,
+            `    - name: ${name}`,
+            `      alias: gemini-3-${minor}-${family}-preview-customtools`,
+          ])
+          .join('\n');
+
+      const initialConfig = `# CLIProxyAPI config generated by CCS v12
+port: 8317
+api-keys:
+  - "ccs-internal-managed"
+auth-dir: "${cliproxyDir.replace(/\\/g, '/')}/auth"
+oauth-model-alias:
+  antigravity:
+${buildGuessedRange('gemini-3-pro-high', 'pro')}
+${buildGuessedRange('gemini-3-flash', 'flash')}
+    - name: custom-model
+      alias: keep-me
+`;
+      fs.writeFileSync(path.join(cliproxyDir, 'config.yaml'), initialConfig);
+
+      regenerateConfig();
+
+      const newConfig = fs.readFileSync(path.join(cliproxyDir, 'config.yaml'), 'utf-8');
+      for (const minor of guessedMinors) {
+        assert(
+          !newConfig.includes(`alias: gemini-3.${minor}-pro-preview`),
+          `Should remove stale generated Pro aliases for 3.${minor}`
+        );
+        assert(
+          !newConfig.includes(`alias: gemini-3-${minor}-flash-preview-customtools`),
+          `Should remove stale generated Flash aliases for 3.${minor}`
+        );
+      }
+      assert(newConfig.includes('alias: keep-me'), 'Should preserve true custom aliases');
+      assert(
+        newConfig.includes('alias: gemini-3-pro-preview'),
+        'Should still keep current baseline Pro preview alias'
+      );
+      assert(
+        newConfig.includes('alias: gemini-3.1-flash-preview-customtools'),
+        'Should still keep current baseline Flash compatibility alias'
+      );
+    });
+
+    it('preserves sparse manual minor-version overrides when a stale guessed range is pruned', () => {
+      const cliproxyDir = path.join(testDir, '.ccs', 'cliproxy');
+      fs.mkdirSync(cliproxyDir, { recursive: true });
+      const guessedMinors = ['3', '4', '5', '6'];
+      const staleRange = guessedMinors
+        .flatMap((minor) => [
+          `    - name: gemini-3-pro-high`,
+          `      alias: gemini-3.${minor}-pro-preview`,
+          `    - name: gemini-3-pro-high`,
+          `      alias: gemini-3.${minor}-pro-preview-customtools`,
+          `    - name: gemini-3-pro-high`,
+          `      alias: gemini-3-${minor}-pro-preview`,
+          `    - name: gemini-3-pro-high`,
+          `      alias: gemini-3-${minor}-pro-preview-customtools`,
+        ])
+        .join('\n');
+
+      const initialConfig = `# CLIProxyAPI config generated by CCS v12
+port: 8317
+api-keys:
+  - "ccs-internal-managed"
+auth-dir: "${cliproxyDir.replace(/\\/g, '/')}/auth"
+oauth-model-alias:
+  antigravity:
+    - name: gemini-3-pro-high
+      alias: gemini-3.2-pro-preview
+${staleRange}
+`;
+      fs.writeFileSync(path.join(cliproxyDir, 'config.yaml'), initialConfig);
+
+      regenerateConfig();
+
+      const newConfig = fs.readFileSync(path.join(cliproxyDir, 'config.yaml'), 'utf-8');
+      assert(
+        newConfig.includes('alias: gemini-3.2-pro-preview'),
+        'Should preserve sparse manual minor-version override'
+      );
+      assert(
+        newConfig.includes('alias: gemini-3.2-pro-preview-customtools'),
+        'Should still expand compatibility aliases for preserved sparse manual override'
+      );
+      for (const minor of guessedMinors) {
+        assert(
+          !newConfig.includes(`alias: gemini-3.${minor}-pro-preview`),
+          `Should prune stale guessed aliases for 3.${minor}`
+        );
+      }
+    });
+
+    it('preserves a manual 3.2 compatibility cluster while pruning higher stale guessed minors', () => {
+      const cliproxyDir = path.join(testDir, '.ccs', 'cliproxy');
+      fs.mkdirSync(cliproxyDir, { recursive: true });
+      const guessedMinors = ['3', '4', '5', '6'];
+      const staleRange = guessedMinors
+        .flatMap((minor) => [
+          `    - name: gemini-3-pro-high`,
+          `      alias: gemini-3.${minor}-pro-preview`,
+          `    - name: gemini-3-pro-high`,
+          `      alias: gemini-3.${minor}-pro-preview-customtools`,
+          `    - name: gemini-3-pro-high`,
+          `      alias: gemini-3-${minor}-pro-preview`,
+          `    - name: gemini-3-pro-high`,
+          `      alias: gemini-3-${minor}-pro-preview-customtools`,
+        ])
+        .join('\n');
+
+      const initialConfig = `# CLIProxyAPI config generated by CCS v12
+port: 8317
+api-keys:
+  - "ccs-internal-managed"
+auth-dir: "${cliproxyDir.replace(/\\/g, '/')}/auth"
+oauth-model-alias:
+  antigravity:
+    - name: gemini-3-pro-high
+      alias: gemini-3.2-pro-preview
+    - name: gemini-3-pro-high
+      alias: gemini-3.2-pro-preview-customtools
+    - name: gemini-3-pro-high
+      alias: gemini-3-2-pro-preview
+    - name: gemini-3-pro-high
+      alias: gemini-3-2-pro-preview-customtools
+${staleRange}
+`;
+      fs.writeFileSync(path.join(cliproxyDir, 'config.yaml'), initialConfig);
+
+      regenerateConfig();
+
+      const newConfig = fs.readFileSync(path.join(cliproxyDir, 'config.yaml'), 'utf-8');
+      assert(
+        newConfig.includes('alias: gemini-3.2-pro-preview'),
+        'Should preserve the manual 3.2 compatibility cluster during legacy cleanup'
+      );
+      assert(
+        newConfig.includes('alias: gemini-3-2-pro-preview-customtools'),
+        'Should preserve hyphenated manual compatibility aliases for 3.2'
+      );
+      for (const minor of guessedMinors) {
+        assert(
+          !newConfig.includes(`alias: gemini-3.${minor}-pro-preview`),
+          `Should prune higher stale guessed aliases for 3.${minor}`
+        );
+      }
+    });
+
+    it('prunes partially retained broad guessed ranges during legacy cleanup', () => {
+      const cliproxyDir = path.join(testDir, '.ccs', 'cliproxy');
+      fs.mkdirSync(cliproxyDir, { recursive: true });
+      const guessedMinors = ['3', '4', '5'];
+      const partialRange = guessedMinors
+        .flatMap((minor) => [
+          `    - name: gemini-3-pro-high`,
+          `      alias: gemini-3.${minor}-pro-preview`,
+          `    - name: gemini-3-pro-high`,
+          `      alias: gemini-3.${minor}-pro-preview-customtools`,
+        ])
+        .join('\n');
+
+      const initialConfig = `# CLIProxyAPI config generated by CCS v12
+port: 8317
+api-keys:
+  - "ccs-internal-managed"
+auth-dir: "${cliproxyDir.replace(/\\/g, '/')}/auth"
+oauth-model-alias:
+  antigravity:
+${partialRange}
+`;
+      fs.writeFileSync(path.join(cliproxyDir, 'config.yaml'), initialConfig);
+
+      regenerateConfig();
+
+      const newConfig = fs.readFileSync(path.join(cliproxyDir, 'config.yaml'), 'utf-8');
+      for (const minor of guessedMinors) {
+        assert(
+          !newConfig.includes(`alias: gemini-3.${minor}-pro-preview`),
+          `Should prune partially retained guessed aliases for 3.${minor}`
+        );
+      }
+    });
+
+    it('preserves manual high-only multi-version clusters that are not broad guessed ranges', () => {
+      const cliproxyDir = path.join(testDir, '.ccs', 'cliproxy');
+      fs.mkdirSync(cliproxyDir, { recursive: true });
+
+      const initialConfig = `# CLIProxyAPI config generated by CCS v12
+port: 8317
+api-keys:
+  - "ccs-internal-managed"
+auth-dir: "${cliproxyDir.replace(/\\/g, '/')}/auth"
+oauth-model-alias:
+  antigravity:
+    - name: gemini-3-pro-high
+      alias: gemini-3.3-pro-preview
+    - name: gemini-3-pro-high
+      alias: gemini-3.3-pro-preview-customtools
+    - name: gemini-3-pro-high
+      alias: gemini-3.4-pro-preview
+    - name: gemini-3-pro-high
+      alias: gemini-3.4-pro-preview-customtools
+`;
+      fs.writeFileSync(path.join(cliproxyDir, 'config.yaml'), initialConfig);
+
+      regenerateConfig();
+
+      const newConfig = fs.readFileSync(path.join(cliproxyDir, 'config.yaml'), 'utf-8');
+      assert(
+        newConfig.includes('alias: gemini-3.3-pro-preview'),
+        'Should preserve manual 3.3 aliases when the cluster is not broad enough to infer stale fan-out'
+      );
+      assert(
+        newConfig.includes('alias: gemini-3.4-pro-preview-customtools'),
+        'Should preserve manual 3.4 compatibility aliases when provenance is ambiguous'
+      );
+    });
+
+    it('preserves single-minor high-version aliases when they are not part of a guessed range', () => {
+      const cliproxyDir = path.join(testDir, '.ccs', 'cliproxy');
+      fs.mkdirSync(cliproxyDir, { recursive: true });
+
+      const initialConfig = `# CLIProxyAPI config generated by CCS v12
+port: 8317
+api-keys:
+  - "ccs-internal-managed"
+auth-dir: "${cliproxyDir.replace(/\\/g, '/')}/auth"
+oauth-model-alias:
+  antigravity:
+    - name: gemini-3-pro-high
+      alias: gemini-3.11-pro-preview
+    - name: gemini-3-pro-high
+      alias: gemini-3.11-pro-preview-customtools
+`;
+      fs.writeFileSync(path.join(cliproxyDir, 'config.yaml'), initialConfig);
+
+      regenerateConfig();
+
+      const newConfig = fs.readFileSync(path.join(cliproxyDir, 'config.yaml'), 'utf-8');
+      assert(
+        newConfig.includes('alias: gemini-3.11-pro-preview'),
+        'Should preserve lone manual high-version aliases during legacy cleanup'
+      );
+      assert(
+        newConfig.includes('alias: gemini-3.11-pro-preview-customtools'),
+        'Should still expand compatibility aliases for preserved high-version aliases'
+      );
+    });
+
+    it('writes a one-time backup before pruning legacy Gemini aliases during migration', () => {
+      const cliproxyDir = path.join(testDir, '.ccs', 'cliproxy');
+      fs.mkdirSync(cliproxyDir, { recursive: true });
+      const configPath = path.join(cliproxyDir, 'config.yaml');
+      const guessedMinors = ['3', '4', '5'];
+      const staleRange = guessedMinors
+        .flatMap((minor) => [
+          `    - name: gemini-3-pro-high`,
+          `      alias: gemini-3.${minor}-pro-preview`,
+          `    - name: gemini-3-pro-high`,
+          `      alias: gemini-3.${minor}-pro-preview-customtools`,
+        ])
+        .join('\n');
+
+      const initialConfig = `# CLIProxyAPI config generated by CCS v12
+port: 8317
+api-keys:
+  - "ccs-internal-managed"
+auth-dir: "${cliproxyDir.replace(/\\/g, '/')}/auth"
+oauth-model-alias:
+  antigravity:
+${staleRange}
+`;
+      fs.writeFileSync(configPath, initialConfig);
+
+      regenerateConfig();
+
+      const backupPath = `${configPath}.pre-v16-gemini-alias-cleanup.bak`;
+      assert(fs.existsSync(backupPath), 'Should keep a backup of the legacy config before pruning');
+      assert(
+        fs.readFileSync(backupPath, 'utf-8').includes('gemini-3.5-pro-preview'),
+        'Should preserve the pruned legacy alias in the migration backup'
+      );
+    });
+
+    it('preserves manual Gemini preview overrides on built-in alias names', () => {
+      const cliproxyDir = path.join(testDir, '.ccs', 'cliproxy');
+      fs.mkdirSync(cliproxyDir, { recursive: true });
+
+      const initialConfig = `# CLIProxyAPI config generated by CCS v12
+port: 8317
+api-keys:
+  - "ccs-internal-managed"
+auth-dir: "${cliproxyDir.replace(/\\/g, '/')}/auth"
+oauth-model-alias:
+  antigravity:
+    - name: gemini-3-pro-high
+      alias: gemini-3.2-pro-preview
+    - name: gemini-3-flash
+      alias: gemini-3.2-flash-preview
+      fork: true
+`;
+      fs.writeFileSync(path.join(cliproxyDir, 'config.yaml'), initialConfig);
+
+      regenerateConfig();
+
+      const newConfig = fs.readFileSync(path.join(cliproxyDir, 'config.yaml'), 'utf-8');
+      assert(
+        newConfig.includes('alias: gemini-3.2-pro-preview'),
+        'Should preserve manual Pro preview overrides on built-in alias names'
+      );
+      assert(
+        newConfig.includes('alias: gemini-3.2-flash-preview'),
+        'Should preserve manual Flash preview overrides on built-in alias names'
+      );
+      assert(
+        newConfig.includes('alias: gemini-3.2-pro-preview-customtools'),
+        'Should still expand compatibility aliases for preserved manual Pro override'
+      );
+      assert(
+        newConfig.includes('alias: gemini-3.2-flash-preview-customtools'),
+        'Should still expand compatibility aliases for preserved manual Flash override'
+      );
+
+      const lines = newConfig.split('\n');
+      for (let i = 0; i < lines.length; i++) {
+        if (lines[i].includes('alias: gemini-3.2-flash-preview')) {
+          assert(
+            lines[i + 1] && lines[i + 1].trim() === 'fork: true',
+            'Should preserve fork: true on manual Flash preview override'
+          );
+          break;
+        }
+      }
+    });
+
+    it('preserves manual Gemini preview compatibility clusters on built-in alias names', () => {
+      const cliproxyDir = path.join(testDir, '.ccs', 'cliproxy');
+      fs.mkdirSync(cliproxyDir, { recursive: true });
+
+      const initialConfig = `# CLIProxyAPI config generated by CCS v12
+port: 8317
+api-keys:
+  - "ccs-internal-managed"
+auth-dir: "${cliproxyDir.replace(/\\/g, '/')}/auth"
+oauth-model-alias:
+  antigravity:
+    - name: gemini-3-pro-high
+      alias: gemini-3.2-pro-preview
+    - name: gemini-3-pro-high
+      alias: gemini-3.2-pro-preview-customtools
+    - name: gemini-3-pro-high
+      alias: gemini-3-2-pro-preview
+    - name: gemini-3-pro-high
+      alias: gemini-3-2-pro-preview-customtools
+`;
+      fs.writeFileSync(path.join(cliproxyDir, 'config.yaml'), initialConfig);
+
+      regenerateConfig();
+
+      const newConfig = fs.readFileSync(path.join(cliproxyDir, 'config.yaml'), 'utf-8');
+      assert(
+        newConfig.includes('alias: gemini-3.2-pro-preview'),
+        'Should preserve manual dotted Pro preview override'
+      );
+      assert(
+        newConfig.includes('alias: gemini-3.2-pro-preview-customtools'),
+        'Should preserve manual dotted Pro customtools override'
+      );
+      assert(
+        newConfig.includes('alias: gemini-3-2-pro-preview'),
+        'Should preserve manual hyphenated Pro preview override'
+      );
+      assert(
+        newConfig.includes('alias: gemini-3-2-pro-preview-customtools'),
+        'Should preserve manual hyphenated Pro customtools override'
+      );
+    });
+
+    it('does not re-prune multi-version manual clusters once the config is already migrated', () => {
+      const cliproxyDir = path.join(testDir, '.ccs', 'cliproxy');
+      fs.mkdirSync(cliproxyDir, { recursive: true });
+
+      const initialConfig = `# CLIProxyAPI config generated by CCS v16
+port: 8317
+api-keys:
+  - "ccs-internal-managed"
+auth-dir: "${cliproxyDir.replace(/\\/g, '/')}/auth"
+oauth-model-alias:
+  antigravity:
+    - name: gemini-3-pro-high
+      alias: gemini-3.2-pro-preview
+    - name: gemini-3-pro-high
+      alias: gemini-3.3-pro-preview
+    - name: gemini-3-pro-high
+      alias: gemini-3.4-pro-preview
+`;
+      fs.writeFileSync(path.join(cliproxyDir, 'config.yaml'), initialConfig);
+
+      regenerateConfig();
+
+      const newConfig = fs.readFileSync(path.join(cliproxyDir, 'config.yaml'), 'utf-8');
+      assert(
+        newConfig.includes('alias: gemini-3.2-pro-preview'),
+        'Should preserve manual aliases after legacy migration has already run'
+      );
+      assert(
+        newConfig.includes('alias: gemini-3.3-pro-preview'),
+        'Should not re-prune later manual version clusters on v16+ configs'
+      );
+      assert(
+        newConfig.includes('alias: gemini-3.4-pro-preview'),
+        'Should leave already-migrated multi-version manual aliases untouched'
+      );
+    });
+
     it('preserves user-added aliases with fork during regeneration', () => {
       const cliproxyDir = path.join(testDir, '.ccs', 'cliproxy');
       fs.mkdirSync(cliproxyDir, { recursive: true });