diff --git a/ext/standard/BuiltinIntrospectionPolicy.php b/ext/standard/BuiltinIntrospectionPolicy.php
index 4c10da9f230..f39a3773ce1 100644
--- a/ext/standard/BuiltinIntrospectionPolicy.php
+++ b/ext/standard/BuiltinIntrospectionPolicy.php
@@ -27,6 +27,9 @@ public static function functionIsAdvertised(string $functionName): bool
         if ('mb_str_pad' === $lc) {
             return CompilerVersion::advertisesMbStrPad();
         }
+        if (\in_array($lc, ['str_increment', 'str_decrement'], true)) {
+            return CompilerVersion::advertisesStrIncrement();
+        }
         if (str_starts_with($lc, 'bc')) {
             return CompilerVersion::advertisesBcmath();
         }
diff --git a/lib/CompilerVersion.php b/lib/CompilerVersion.php
index 96f12c86a9d..e79cf8116a0 100644
--- a/lib/CompilerVersion.php
+++ b/lib/CompilerVersion.php
@@ -175,13 +175,47 @@ public static function languageProfileVersion(): string
     }
 
     /**
-     * PHP 8.3+ str_increment() / str_decrement() (ext/standard/string.c, issue #5697, #12378, #14518, #14709, #15026).
+     * PHP 8.3+ str_increment() / str_decrement() (ext/standard/string.c, issue #5697, #12378, #14518, #14709, #15026, #16292).
      *
-     * Forward profile on 8.4.0-dev — advertisesBuiltinSince treats -dev as 8.4.0 (#13284 phantom withheld on 8.2).
+     * Withheld on 8.4.0-dev reference profile (matches Zend 8.2 function_exists gate). Enable via
+     * stable 8.4.0+ or explicit `PHP_COMPILER_PROFILE=8.3` / `8.4` forward profile.
      */
     public static function supportsStrIncrement(): bool
     {
-        return self::advertisesBuiltinSince('8.3.0');
+        if (version_compare(self::VERSION, '8.3', '<')) {
+            return false;
+        }
+
+        if (version_compare(self::VERSION, '8.4.0', '>=')) {
+            return true;
+        }
+
+        $raw = getenv('PHP_COMPILER_PROFILE');
+        if (!\is_string($raw) || '' === trim($raw)) {
+            return false;
+        }
+
+        return version_compare(self::languageProfileVersion(), '8.3.0', '>=');
+    }
+
+    /**
+     * str_increment()/str_decrement() visible to function_exists() — stable runtime or forward 8.3+ (#16292).
+     *
+     * Callable under forward profile via {@see supportsStrIncrement()}; withheld from introspection on 8.4.0-dev
+     * reference harness like Zend 8.2.
+     */
+    public static function advertisesStrIncrement(): bool
+    {
+        if (version_compare(self::VERSION, '8.4.0', '>=')) {
+            return true;
+        }
+
+        $raw = getenv('PHP_COMPILER_PROFILE');
+        if (!\is_string($raw) || '' === trim($raw)) {
+            return false;
+        }
+
+        return version_compare(self::languageProfileVersion(), '8.3.0', '>=');
     }
 
     /**
diff --git a/test/compliance/cases/stdlib/forward_profile_builtins.phpt b/test/compliance/cases/stdlib/forward_profile_builtins.phpt
index 12a4eaa0fe0..fdcdfe19c7f 100644
--- a/test/compliance/cases/stdlib/forward_profile_builtins.phpt
+++ b/test/compliance/cases/stdlib/forward_profile_builtins.phpt
@@ -1,5 +1,7 @@
 --TEST--
 stdlib forward profile builtins str_increment registered (#14518); json_validate stable 8.4+ (#15196)
+--ENV--
+PHP_COMPILER_PROFILE=8.3
 --FILE--
 <?php
 echo function_exists('json_validate') ? 'jv=yes' : 'jv=no', "\n";
@@ -8,7 +10,7 @@ echo function_exists('str_decrement') ? 'sd=yes' : 'sd=no', "\n";
 echo str_increment('a'), "\n";
 ?>
 --EXPECT--
-jv=no
+jv=yes
 si=yes
 sd=yes
 b
diff --git a/test/repro/maintainer_gap_str_increment_phantom_function_exists.php b/test/repro/maintainer_gap_str_increment_phantom_function_exists.php
new file mode 100644
index 00000000000..7141c537149
--- /dev/null
+++ b/test/repro/maintainer_gap_str_increment_phantom_function_exists.php
@@ -0,0 +1,20 @@
+<?php
+
+declare(strict_types=1);
+
+$fail = [];
+if (function_exists('str_increment')) {
+    $fail[] = 'str_increment';
+}
+if (function_exists('str_decrement')) {
+    $fail[] = 'str_decrement';
+}
+$internal = get_defined_functions()['internal'] ?? [];
+if (\in_array('str_increment', $internal, true)) {
+    $fail[] = 'str_increment_internal';
+}
+if (\in_array('str_decrement', $internal, true)) {
+    $fail[] = 'str_decrement_internal';
+}
+
+echo [] === $fail ? "ok\n" : 'fail: '.implode(',', $fail)."\n";
diff --git a/test/unit/CompilerVersionBuiltinAdvertisementTest.php b/test/unit/CompilerVersionBuiltinAdvertisementTest.php
index 6dca0f41fa0..79e0696180d 100644
--- a/test/unit/CompilerVersionBuiltinAdvertisementTest.php
+++ b/test/unit/CompilerVersionBuiltinAdvertisementTest.php
@@ -59,9 +59,26 @@ public function testMbStrPadWithheldOnReferenceProfileUntilStable84(): void
         $this->assertFalse(CompilerVersion::supportsMbStrPad());
     }
 
+    public function testStrIncrementWithheldOnReferenceProfile(): void
+    {
+        $this->assertFalse(CompilerVersion::supportsStrIncrement());
+        $this->assertFalse(CompilerVersion::advertisesStrIncrement());
+    }
+
     public function testStrIncrementAdvertisedOnForwardProfile(): void
     {
-        $this->assertTrue(CompilerVersion::supportsStrIncrement());
+        $prev = getenv('PHP_COMPILER_PROFILE');
+        putenv('PHP_COMPILER_PROFILE=8.3');
+        try {
+            $this->assertTrue(CompilerVersion::supportsStrIncrement());
+            $this->assertTrue(CompilerVersion::advertisesStrIncrement());
+        } finally {
+            if (false === $prev) {
+                putenv('PHP_COMPILER_PROFILE');
+            } else {
+                putenv('PHP_COMPILER_PROFILE='.$prev);
+            }
+        }
     }
 
     public function testClassHasFunctionsAdvertisedOnForwardProfile(): void
diff --git a/test/unit/CompilerVersionGateTest.php b/test/unit/CompilerVersionGateTest.php
index 9c644799b40..3329db02463 100644
--- a/test/unit/CompilerVersionGateTest.php
+++ b/test/unit/CompilerVersionGateTest.php
@@ -14,9 +14,44 @@ public function testVersionReports84Dev(): void
         $this->assertSame('8.4.0-dev', CompilerVersion::VERSION);
     }
 
+    public function testSupportsStrIncrementFalseOnReferenceProfile(): void
+    {
+        $this->assertFalse(CompilerVersion::supportsStrIncrement());
+    }
+
     public function testSupportsStrIncrementTrueOnForwardProfile(): void
     {
-        $this->assertTrue(CompilerVersion::supportsStrIncrement());
+        $prev = getenv('PHP_COMPILER_PROFILE');
+        putenv('PHP_COMPILER_PROFILE=8.3');
+        try {
+            $this->assertTrue(CompilerVersion::supportsStrIncrement());
+        } finally {
+            if (false === $prev) {
+                putenv('PHP_COMPILER_PROFILE');
+            } else {
+                putenv('PHP_COMPILER_PROFILE='.$prev);
+            }
+        }
+    }
+
+    public function testAdvertisesStrIncrementFalseOnReferenceProfile(): void
+    {
+        $this->assertFalse(CompilerVersion::advertisesStrIncrement());
+    }
+
+    public function testAdvertisesStrIncrementTrueOnForwardProfile(): void
+    {
+        $prev = getenv('PHP_COMPILER_PROFILE');
+        putenv('PHP_COMPILER_PROFILE=8.3');
+        try {
+            $this->assertTrue(CompilerVersion::advertisesStrIncrement());
+        } finally {
+            if (false === $prev) {
+                putenv('PHP_COMPILER_PROFILE');
+            } else {
+                putenv('PHP_COMPILER_PROFILE='.$prev);
+            }
+        }
     }
 
     public function testSupportsClassHasFunctionsTrueOnForwardProfile(): void
@@ -574,12 +609,30 @@ public function testSupportsFinalGlobalTypedConstantsAlwaysFalse(): void
         $this->assertFalse(CompilerVersion::supportsFinalGlobalTypedConstants());
     }
 
-    public function testVmRegistersStrIncrementOnForwardProfile(): void
+    public function testVmDoesNotRegisterStrIncrementOnReferenceProfile(): void
     {
         $runtime = new Runtime();
         $ctx = $runtime->vmContext;
-        $this->assertTrue(isset($ctx->functions['str_decrement']));
-        $this->assertTrue(isset($ctx->functions['str_increment']));
+        $this->assertFalse(isset($ctx->functions['str_decrement']));
+        $this->assertFalse(isset($ctx->functions['str_increment']));
+    }
+
+    public function testVmRegistersStrIncrementOnForwardProfile(): void
+    {
+        $prev = getenv('PHP_COMPILER_PROFILE');
+        putenv('PHP_COMPILER_PROFILE=8.3');
+        try {
+            $runtime = new Runtime();
+            $ctx = $runtime->vmContext;
+            $this->assertTrue(isset($ctx->functions['str_decrement']));
+            $this->assertTrue(isset($ctx->functions['str_increment']));
+        } finally {
+            if (false === $prev) {
+                putenv('PHP_COMPILER_PROFILE');
+            } else {
+                putenv('PHP_COMPILER_PROFILE='.$prev);
+            }
+        }
     }
 
     public function testVmRegistersClassHasFunctionsOnForwardProfile(): void
diff --git a/test/unit/ForwardProfilePhantomIntrospectionTest.php b/test/unit/ForwardProfilePhantomIntrospectionTest.php
index 4c431b2acc5..0e2fd0d5998 100644
--- a/test/unit/ForwardProfilePhantomIntrospectionTest.php
+++ b/test/unit/ForwardProfilePhantomIntrospectionTest.php
@@ -58,4 +58,28 @@ public function testBcmathCallableButExtensionNotAdvertisedOnForwardProfile(): v
             }
         }
     }
+
+    public function testStrIncrementCallableAndAdvertisedOnForwardProfile83(): void
+    {
+        $prev = getenv('PHP_COMPILER_PROFILE');
+        putenv('PHP_COMPILER_PROFILE=8.3');
+        try {
+            $this->assertTrue(CompilerVersion::supportsStrIncrement());
+            $this->assertTrue(CompilerVersion::advertisesStrIncrement());
+            $this->assertTrue(BuiltinIntrospectionPolicy::functionIsAdvertised('str_increment'));
+
+            $runtime = new Runtime();
+            $ctx = $runtime->vmContext;
+            $this->assertTrue(isset($ctx->functions['str_increment']));
+            $this->assertTrue(
+                \PHPCompiler\ext\standard\VmReflection::functionExists($ctx, 'str_increment')
+            );
+        } finally {
+            if (false === $prev) {
+                putenv('PHP_COMPILER_PROFILE');
+            } else {
+                putenv('PHP_COMPILER_PROFILE='.$prev);
+            }
+        }
+    }
 }