diff --git a/src/applications/cache/spec/PhabricatorDataCacheSpec.php b/src/applications/cache/spec/PhabricatorDataCacheSpec.php
--- a/src/applications/cache/spec/PhabricatorDataCacheSpec.php
+++ b/src/applications/cache/spec/PhabricatorDataCacheSpec.php
@@ -33,8 +33,6 @@
     if (ini_get('apc.enabled')) {
       if (function_exists('apcu_clear_cache')) {
         $clear_callback = 'apcu_clear_cache';
-      } else {
-        $clear_callback = 'apc_clear_cache';
       }
 
       $this
@@ -67,9 +65,6 @@
     if (function_exists('apcu_sma_info')) {
       $mem = apcu_sma_info();
       $info = apcu_cache_info();
-    } else if (function_exists('apc_sma_info')) {
-      $mem = apc_sma_info();
-      $info = apc_cache_info('user');
     } else {
       $mem = null;
     }
diff --git a/src/infrastructure/cache/PhutilAPCKeyValueCache.php b/src/infrastructure/cache/PhutilAPCKeyValueCache.php
--- a/src/infrastructure/cache/PhutilAPCKeyValueCache.php
+++ b/src/infrastructure/cache/PhutilAPCKeyValueCache.php
@@ -11,7 +11,7 @@
 
 
   public function isAvailable() {
-    return (function_exists('apc_fetch') || function_exists('apcu_fetch')) &&
+    return function_exists('apcu_fetch') &&
            ini_get('apc.enabled') &&
            (ini_get('apc.enable_cli') || php_sapi_name() != 'cli');
   }
@@ -27,8 +27,6 @@
     foreach ($keys as $key) {
       if ($is_apcu) {
         $result = apcu_fetch($key, $fetched);
-      } else {
-        $result = apc_fetch($key, $fetched);
       }
 
       if ($fetched) {
@@ -48,8 +46,8 @@
       $ttl = 0;
     }
 
-    // NOTE: Although modern APC supports passing an array to `apc_store()`,
-    // it is not supported by older version of APC or by HPHP.
+    // NOTE: Although late APC supported passing an array to `apc_store()`,
+    // it was not supported by older versions of APC or by HPHP.
 
     // See T13525 for discussion of use of "@" to silence this warning:
     // > GC cache entry "<some-key-name>" was on gc-list for <X> seconds
@@ -57,8 +55,6 @@
     foreach ($keys as $key => $value) {
       if ($is_apcu) {
         @apcu_store($key, $value, $ttl);
-      } else {
-        @apc_store($key, $value, $ttl);
       }
     }
 
@@ -74,8 +70,6 @@
     foreach ($keys as $key) {
       if ($is_apcu) {
         apcu_delete($key);
-      } else {
-        apc_delete($key);
       }
     }
 
@@ -90,8 +84,6 @@
 
     if ($is_apcu) {
       apcu_clear_cache();
-    } else {
-      apc_clear_cache('user');
     }
 
     return $this;
diff --git a/src/infrastructure/cache/__tests__/PhutilKeyValueCacheTestCase.php b/src/infrastructure/cache/__tests__/PhutilKeyValueCacheTestCase.php
--- a/src/infrastructure/cache/__tests__/PhutilKeyValueCacheTestCase.php
+++ b/src/infrastructure/cache/__tests__/PhutilKeyValueCacheTestCase.php
@@ -234,9 +234,9 @@
 
 
     // NOTE: The TTL tests are necessarily slow (we must sleep() through the
-    // TTLs) and do not work with APC (it does not TTL until the next request)
-    // so they're disabled by default. If you're developing the cache stack,
-    // it may be useful to run them.
+    // TTLs) and did not work with old APC (it does not TTL until the next
+    // request) so they're disabled by default. If you're developing the cache
+    // stack, it may be useful to run them.
 
     return;
 
diff --git a/support/startup/PhabricatorClientLimit.php b/support/startup/PhabricatorClientLimit.php
--- a/support/startup/PhabricatorClientLimit.php
+++ b/support/startup/PhabricatorClientLimit.php
@@ -37,10 +37,10 @@
     // NOTE: We can not use pht() here because this runs before libraries
     // load.
 
-    if (!function_exists('apc_fetch') && !function_exists('apcu_fetch')) {
+    if (!function_exists('apcu_fetch')) {
       throw new Exception(
-        'You can not configure connection rate limits unless APC/APCu are '.
-        'available. Rate limits rely on APC/APCu to track clients and '.
+        'You can not configure connection rate limits unless APCu is '.
+        'available. Rate limits rely on APCu to track clients and '.
         'connections.');
     }
 
@@ -199,8 +199,6 @@
 
     if ($is_apcu) {
       $bucket = apcu_fetch($bucket_key);
-    } else {
-      $bucket = apc_fetch($bucket_key);
     }
 
     if (!is_array($bucket)) {
@@ -216,8 +214,6 @@
 
     if ($is_apcu) {
       @apcu_store($bucket_key, $bucket);
-    } else {
-      @apc_store($bucket_key, $bucket);
     }
 
     return $this;
@@ -237,8 +233,6 @@
     $min_key = $this->getMinimumBucketCacheKey();
     if ($is_apcu) {
       $min = apcu_fetch($min_key);
-    } else {
-      $min = apc_fetch($min_key);
     }
 
     // If we don't have any buckets stored yet, store the current bucket as
@@ -247,8 +241,6 @@
     if (!$min) {
       if ($is_apcu) {
         @apcu_store($min_key, $cur);
-      } else {
-        @apc_store($min_key, $cur);
       }
       $min = $cur;
     }
@@ -262,9 +254,6 @@
       if ($is_apcu) {
         apcu_delete($bucket_key);
         @apcu_store($min_key, $cursor + 1);
-      } else {
-        apc_delete($bucket_key);
-        @apc_store($min_key, $cursor + 1);
       }
     }
 
@@ -276,8 +265,6 @@
       $bucket_key = $this->getBucketCacheKey($cursor);
       if ($is_apcu) {
         $bucket = apcu_fetch($bucket_key);
-      } else {
-        $bucket = apc_fetch($bucket_key);
       }
       if (isset($bucket[$client_key])) {
         $score += $bucket[$client_key];
diff --git a/support/startup/PhabricatorStartup.php b/support/startup/PhabricatorStartup.php
--- a/support/startup/PhabricatorStartup.php
+++ b/support/startup/PhabricatorStartup.php
@@ -557,22 +557,6 @@
       }
     }
 
-    if (extension_loaded('apc')) {
-      $apc_version = phpversion('apc');
-      $known_bad = array(
-        '3.1.14' => true,
-        '3.1.15' => true,
-        '3.1.15-dev' => true,
-      );
-      if (isset($known_bad[$apc_version])) {
-        self::didFatal(
-          "You have APC {$apc_version} installed. This version of APC is ".
-          "known to be bad, and does not work with Phorge (it will cause ".
-          "Phorge to fatal unrecoverably with nonsense errors).".
-          "Downgrade to version 3.1.13.");
-      }
-    }
-
     if (isset($_SERVER['HTTP_PROXY'])) {
       self::didFatal(
         'This HTTP request included a "Proxy:" header, poisoning the '.