diff --git a/docs/capabilities.md b/docs/capabilities.md
index 674daa8ca89..41bf9345b4c 100644
--- a/docs/capabilities.md
+++ b/docs/capabilities.md
@@ -46,7 +46,7 @@ Auto-generated by `script/capability-matrix.php`. Do not edit by hand.
 | `array_product` | yes | yes | yes | standard | JIT PHPT; AOT PHPT |
 | `array_push` | yes | yes | yes | standard | doc: VM only; JIT PHPT; AOT PHPT |
 | `array_rand` | yes | yes | yes | standard | JIT PHPT; AOT PHPT |
-| `array_reduce` | yes | yes | yes | standard | callbacks: string user functions + VM closures; php-src-strict invalid callback TypeError (#6679); JIT PHPT |
+| `array_reduce` | yes | yes | yes | standard | JIT PHPT |
 | `array_replace` | yes | yes | yes | standard | JIT PHPT; AOT PHPT |
 | `array_replace_recursive` | yes | yes | yes | standard | AOT PHPT |
 | `array_reverse` | yes | yes | yes | standard | JIT PHPT; AOT PHPT |
@@ -80,7 +80,7 @@ Auto-generated by `script/capability-matrix.php`. Do not edit by hand.
 | `bin2hex` | yes | yes | yes | standard | JIT PHPT; AOT PHPT |
 | `bindec` | yes | yes | yes | standard |  |
 | `boolval` | yes | yes | yes | standard | AOT PHPT |
-| `ceil` | yes | yes | yes | standard |  |
+| `ceil` | yes | yes | yes | standard | JIT PHPT |
 | `chdir` | yes | yes | yes | standard | JIT PHPT; AOT PHPT |
 | `chgrp` | yes | yes | yes | standard | AOT PHPT |
 | `chmod` | yes | yes | yes | standard | JIT PHPT; AOT PHPT |
@@ -141,7 +141,7 @@ Auto-generated by `script/capability-matrix.php`. Do not edit by hand.
 | `disktotalspace` | yes | yes | yes | standard |  |
 | `dl` | yes | yes | yes | standard |  |
 | `doubleval` | yes | yes | yes | standard | JIT PHPT; AOT PHPT |
-| `end` | yes | yes | yes | standard |  |
+| `end` | yes | yes | yes | standard | JIT PHPT |
 | `enum_exists` | yes | yes | yes | standard | JIT PHPT; AOT PHPT |
 | `error_clear_last` | yes | yes | yes | standard | JIT PHPT; AOT PHPT |
 | `error_get_last` | yes | yes | yes | standard | JIT PHPT; AOT PHPT |
@@ -177,12 +177,12 @@ Auto-generated by `script/capability-matrix.php`. Do not edit by hand.
 | `filesize` | yes | yes | yes | standard | JIT PHPT; AOT PHPT |
 | `filetype` | yes | yes | yes | standard | JIT PHPT; AOT PHPT |
 | `filter_id` | yes | yes | yes | filter |  |
-| `filter_input` | yes | yes | yes | standard | AOT PHPT |
+| `filter_input` | yes | yes | yes | standard | JIT PHPT; AOT PHPT |
 | `filter_list` | yes | yes | yes | filter |  |
 | `filter_var` | yes | yes | yes | filter | AOT PHPT |
 | `floatval` | yes | yes | yes | standard | JIT PHPT; AOT PHPT |
 | `flock` | yes | yes | yes | standard | JIT PHPT; AOT PHPT |
-| `floor` | yes | yes | yes | standard |  |
+| `floor` | yes | yes | yes | standard | JIT PHPT |
 | `flush` | yes | yes | yes | standard | JIT PHPT; AOT PHPT |
 | `fmod` | yes | yes | yes | standard |  |
 | `fnmatch` | yes | yes | yes | standard | JIT PHPT; AOT PHPT |
@@ -437,7 +437,7 @@ Auto-generated by `script/capability-matrix.php`. Do not edit by hand.
 | `rewind` | yes | yes | yes | standard | JIT PHPT; AOT PHPT |
 | `rewinddir` | yes | yes | yes | standard | JIT PHPT |
 | `rmdir` | yes | yes | yes | standard | JIT PHPT; AOT PHPT |
-| `round` | yes | yes | yes | standard | AOT PHPT |
+| `round` | yes | yes | yes | standard | JIT PHPT; AOT PHPT |
 | `rsort` | yes | yes | yes | standard | JIT PHPT; AOT PHPT |
 | `rtrim` | yes | yes | yes | standard | JIT PHPT; AOT PHPT |
 | `scandir` | yes | yes | yes | standard | JIT PHPT; AOT PHPT |
@@ -467,7 +467,7 @@ Auto-generated by `script/capability-matrix.php`. Do not edit by hand.
 | `soundex` | yes | yes | yes | standard | JIT PHPT; AOT PHPT |
 | `spl_autoload_register` | yes | yes | yes | standard | JIT PHPT |
 | `sprintf` | yes | yes | yes | standard | JIT PHPT; AOT PHPT |
-| `sqrt` | yes | yes | yes | standard |  |
+| `sqrt` | yes | yes | yes | standard | JIT PHPT |
 | `sscanf` | yes | yes | yes | standard | AOT PHPT |
 | `stat` | yes | yes | yes | standard | JIT PHPT; AOT PHPT |
 | `str_contains` | yes | yes | yes | standard | JIT PHPT; AOT PHPT |
@@ -479,7 +479,7 @@ Auto-generated by `script/capability-matrix.php`. Do not edit by hand.
 | `str_pad` | yes | yes | yes | standard | JIT PHPT; AOT PHPT |
 | `str_repeat` | yes | yes | yes | standard | JIT PHPT; AOT PHPT |
 | `str_replace` | yes | yes | yes | standard | JIT PHPT; AOT PHPT |
-| `str_rot13` | yes | yes | yes | standard | AOT PHPT |
+| `str_rot13` | yes | yes | yes | standard | JIT PHPT; AOT PHPT |
 | `str_shuffle` | yes | yes | yes | standard | JIT PHPT; AOT PHPT |
 | `str_split` | yes | yes | yes | standard | JIT PHPT; AOT PHPT |
 | `str_starts_with` | yes | yes | yes | standard | JIT PHPT; AOT PHPT |
@@ -491,7 +491,8 @@ Auto-generated by `script/capability-matrix.php`. Do not edit by hand.
 | `stream_context_create` | yes | yes | yes | standard | JIT PHPT; AOT PHPT |
 | `stream_get_contents` | yes | yes | yes | standard | AOT PHPT |
 | `stream_get_line` | yes | yes | yes | standard | JIT PHPT; AOT PHPT |
-| `stream_is_local` | yes | yes | yes | standard | AOT PHPT |
+| `stream_is_local` | yes | yes | yes | standard |  |
+| `stream_isatty` | yes | yes | yes | standard |  |
 | `stream_set_chunk_size` | yes | yes | yes | standard | AOT PHPT |
 | `stream_set_read_buffer` | yes | yes | yes | standard | AOT PHPT |
 | `stream_set_timeout` | yes | yes | yes | standard | JIT PHPT; AOT PHPT |
@@ -556,7 +557,7 @@ Auto-generated by `script/capability-matrix.php`. Do not edit by hand.
 | `usleep` | yes | yes | yes | standard | JIT PHPT |
 | `usort` | yes | yes | yes | standard | callbacks: strcmp JIT; strcasecmp VM; VM closure comparator (#3086, #1210); JIT PHPT |
 | `utf8_decode` | yes | yes | yes | standard | AOT PHPT |
-| `utf8_encode` | yes | yes | yes | standard | AOT PHPT |
+| `utf8_encode` | yes | yes | yes | standard | JIT PHPT; AOT PHPT |
 | `var_dump` | yes | yes | yes | standard |  |
 | `var_export` | yes | yes | yes | standard | JIT PHPT; AOT PHPT |
 | `version_compare` | yes | yes | yes | standard | AOT PHPT |
diff --git a/ext/standard/JitStreamIsatty.php b/ext/standard/JitStreamIsatty.php
new file mode 100644
index 00000000000..aa8c5a21274
--- /dev/null
+++ b/ext/standard/JitStreamIsatty.php
@@ -0,0 +1,25 @@
+<?php
+
+declare(strict_types=1);
+
+namespace PHPCompiler\ext\standard;
+
+use PHPCompiler\JIT\Context;
+use PHPLLVM\Builder;
+use PHPLLVM\Value;
+
+/** LLVM lowering for stream_isatty() via __compiler_stream_isatty (issue #6035). */
+final class JitStreamIsatty
+{
+    /** @return Value */
+    public static function invoke(Context $context, Value $handleLong): Value
+    {
+        $ret = $context->builder->call(
+            $context->lookupFunction('__compiler_stream_isatty'),
+            $handleLong
+        );
+        $i32 = $context->getTypeFromString('int32');
+
+        return $context->builder->icmp(Builder::INT_EQ, $ret, $i32->constInt(1, false));
+    }
+}
diff --git a/ext/standard/Module.php b/ext/standard/Module.php
index d46a0364df1..90cf2b16bf5 100755
--- a/ext/standard/Module.php
+++ b/ext/standard/Module.php
@@ -423,6 +423,7 @@ public function getFunctions(): array
             new stream_supports(),
             new stream_supports_lock(),
             new stream_is_local(),
+            new stream_isatty(),
             new fopen(),
             new fread(),
             new stream_get_contents(),
diff --git a/ext/standard/VmFs.php b/ext/standard/VmFs.php
index f023dcbaa54..2d2f3ca39f9 100644
--- a/ext/standard/VmFs.php
+++ b/ext/standard/VmFs.php
@@ -686,6 +686,21 @@ public static function streamSetReadBuffer(int $handle, int $buffer) {
         return (int) $previous;
     }
 
+    /**
+     * stream_isatty() — php-src ext/standard/streamsfuncs.c (issue #6035).
+     *
+     * Returns true when the stream is connected to a terminal (php_stream_isatty).
+     */
+    public static function streamIsatty(int $handle): bool
+    {
+        $fp = self::lookup($handle);
+        if (null === $fp) {
+            return false;
+        }
+
+        return \stream_isatty($fp);
+    }
+
     /**
      * stream_is_local() — php-src ext/standard/streamsfuncs.c (issue #6173).
      *
diff --git a/ext/standard/stream_isatty.php b/ext/standard/stream_isatty.php
new file mode 100644
index 00000000000..265bb75c3ed
--- /dev/null
+++ b/ext/standard/stream_isatty.php
@@ -0,0 +1,51 @@
+<?php
+
+declare(strict_types=1);
+
+namespace PHPCompiler\ext\standard;
+
+use PHPCompiler\Frame;
+use PHPCompiler\Func\Internal;
+use PHPCompiler\JIT\Context;
+use PHPCompiler\JIT\JitLongArg;
+use PHPCompiler\JIT\Variable as JITVariable;
+use PHPLLVM\Value;
+
+/** stream_isatty() — VM via VmFs; JIT/AOT via __compiler_stream_isatty (issue #6035). */
+final class stream_isatty extends Internal
+{
+    public function __construct()
+    {
+        parent::__construct('stream_isatty');
+    }
+
+    public function execute(Frame $frame): void
+    {
+        if (1 !== \count($frame->calledArgs)) {
+            throw new \LogicException('stream_isatty() requires exactly one argument in this compiler build');
+        }
+        $handle = VmStreamArg::requireStreamHandle(
+            $frame->calledArgs[0]->resolveIndirect(),
+            'stream_isatty'
+        );
+        if (null === $frame->returnVar) {
+            return;
+        }
+        $frame->returnVar->bool(VmFs::streamIsatty($handle));
+    }
+
+    public function call(Context $context, JITVariable ...$args): Value
+    {
+        if (1 !== \count($args)) {
+            throw new \LogicException('stream_isatty() requires exactly one argument in this compiler build');
+        }
+
+        return JitStreamIsatty::invoke(
+            $context,
+            $context->builder->truncOrBitCast(
+                JitLongArg::lower($context, $args[0], 'stream_isatty() stream'),
+                $context->getTypeFromString('int64')
+            )
+        );
+    }
+}
diff --git a/lib/AOT/runtime/phpc_stream.c b/lib/AOT/runtime/phpc_stream.c
index 1c55ef6121d..72113a5ad22 100644
--- a/lib/AOT/runtime/phpc_stream.c
+++ b/lib/AOT/runtime/phpc_stream.c
@@ -425,6 +425,28 @@ int __compiler_stream_is_local(int64_t handle)
     return phpc_stream_is_url_path(path) ? 0 : 1;
 }
 
+int __compiler_stream_isatty(int64_t handle)
+{
+    FILE *fp = __phpc_resolve_stream(handle);
+
+    if (NULL == fp) {
+        return 0;
+    }
+#if defined(_WIN32)
+    return _isatty(_fileno(fp)) ? 1 : 0;
+#else
+    {
+        int fd = fileno(fp);
+
+        if (fd < 0) {
+            return 0;
+        }
+
+        return isatty(fd) ? 1 : 0;
+    }
+#endif
+}
+
 int __compiler_stream_supports(int64_t handle, int64_t feature)
 {
     FILE *fp;
diff --git a/lib/JIT/Builtin/Type.php b/lib/JIT/Builtin/Type.php
index 9155660c700..0bfe66ecbbc 100755
--- a/lib/JIT/Builtin/Type.php
+++ b/lib/JIT/Builtin/Type.php
@@ -326,6 +326,9 @@ public function register(): void {
         $fntypeStreamIsLocal = $this->context->context->functionType($i32, false, $i64);
         $fnStreamIsLocal = $this->context->module->addFunction('__compiler_stream_is_local', $fntypeStreamIsLocal);
         $this->context->registerFunction('__compiler_stream_is_local', $fnStreamIsLocal);
+        $fntypeStreamIsatty = $this->context->context->functionType($i32, false, $i64);
+        $fnStreamIsatty = $this->context->module->addFunction('__compiler_stream_isatty', $fntypeStreamIsatty);
+        $this->context->registerFunction('__compiler_stream_isatty', $fnStreamIsatty);
         $fntypeFtruncate = $this->context->context->functionType($i32, false, $i64, $i64);
         $fnFtruncate = $this->context->module->addFunction('__compiler_ftruncate', $fntypeFtruncate);
         $this->context->registerFunction('__compiler_ftruncate', $fnFtruncate);
diff --git a/test/compliance/cases/stdlib/stream_isatty.phpt b/test/compliance/cases/stdlib/stream_isatty.phpt
new file mode 100644
index 00000000000..b7a0c7b3f5f
--- /dev/null
+++ b/test/compliance/cases/stdlib/stream_isatty.phpt
@@ -0,0 +1,17 @@
+--TEST--
+stream_isatty() on php://memory and plainfile (issue #6035, php-src streamsfuncs.c)
+--FILE--
+<?php
+echo function_exists('stream_isatty') ? '1' : '0', "\n";
+$memory = fopen('php://memory', 'r+');
+echo stream_isatty($memory) ? '1' : '0', "\n";
+fclose($memory);
+$path = sys_get_temp_dir() . '/phpc_stream_isatty_' . (string) getmypid() . '.txt';
+$fp = fopen($path, 'w');
+echo stream_isatty($fp) ? '1' : '0', "\n";
+fclose($fp);
+@unlink($path);
+--EXPECT--
+1
+0
+0
diff --git a/test/compliance/cases/stdlib/stream_isatty_enum_typeerror.phpt b/test/compliance/cases/stdlib/stream_isatty_enum_typeerror.phpt
new file mode 100644
index 00000000000..561cd28f882
--- /dev/null
+++ b/test/compliance/cases/stdlib/stream_isatty_enum_typeerror.phpt
@@ -0,0 +1,14 @@
+--TEST--
+stream_isatty() enum case stream operand TypeError (#6035, php-src-strict)
+--FILE--
+<?php
+enum E: int { case A = 1; }
+
+try {
+    stream_isatty(E::A);
+    echo "uncaught\n";
+} catch (TypeError $e) {
+    echo $e->getMessage(), "\n";
+}
+--EXPECT--
+stream_isatty(): Argument #1 ($stream) must be of type resource, E given
diff --git a/test/compliance/cases/stdlib/stream_isatty_typeerror.phpt b/test/compliance/cases/stdlib/stream_isatty_typeerror.phpt
new file mode 100644
index 00000000000..057d5ac018a
--- /dev/null
+++ b/test/compliance/cases/stdlib/stream_isatty_typeerror.phpt
@@ -0,0 +1,12 @@
+--TEST--
+stream_isatty() non-resource operand TypeError (#6035, php-src streamsfuncs.c)
+--FILE--
+<?php
+try {
+    stream_isatty([]);
+    echo "uncaught\n";
+} catch (TypeError $e) {
+    echo $e->getMessage(), "\n";
+}
+--EXPECT--
+stream_isatty(): Argument #1 ($stream) must be of type resource, array given
diff --git a/test/repro/stream_isatty_6035.php b/test/repro/stream_isatty_6035.php
new file mode 100644
index 00000000000..36e00d2af1e
--- /dev/null
+++ b/test/repro/stream_isatty_6035.php
@@ -0,0 +1,5 @@
+<?php
+echo function_exists('stream_isatty') ? '1' : '0', "\n";
+$memory = fopen('php://memory', 'r+');
+echo stream_isatty($memory) ? '1' : '0', "\n";
+fclose($memory);