diff --git a/UnityPy/enums/BundleFile.py b/UnityPy/enums/BundleFile.py
index fec1cf4a..be7dd85d 100644
--- a/UnityPy/enums/BundleFile.py
+++ b/UnityPy/enums/BundleFile.py
@@ -6,7 +6,8 @@ class CompressionFlags(IntFlag):
     LZMA = 1
     LZ4 = 2
     LZ4HC = 3
-    LZHAM = 4
+    COMPRESSION_4 = 4
+    COMPRESSION_5 = 5
 
 
 class ArchiveFlagsOld(IntFlag):
diff --git a/UnityPy/files/BundleFile.py b/UnityPy/files/BundleFile.py
index 3cd650b5..f4eb8681 100644
--- a/UnityPy/files/BundleFile.py
+++ b/UnityPy/files/BundleFile.py
@@ -1,6 +1,7 @@
 # TODO: implement encryption for saving files
 from collections import namedtuple
 import re
+import os
 from typing import Optional, Tuple, Union
 
 from . import File
@@ -486,6 +487,17 @@ def save_web_raw(self, writer: EndianBinaryWriter):
         # Write compressed content
         writer.write(compressed_content)
 
+    @staticmethod
+    def read_long_length_no_check(ip: bytearray, pos: int) -> tuple[int, int]:
+        b = 0
+        l = 0
+        while True:
+            b = ip[pos]
+            pos += 1
+            l += b
+            if b != 255:
+                break
+        return l, pos
 
     def decompress_data(
         self,
@@ -516,8 +528,36 @@ def decompress_data(
             if self.decryptor is not None and flags & 0x100:
                 compressed_data = self.decryptor.decrypt_block(compressed_data, index)
             return CompressionHelper.decompress_lz4(compressed_data, uncompressed_size)
-        elif comp_flag == CompressionFlags.LZHAM:  # LZHAM
-            raise NotImplementedError("LZHAM decompression not implemented")
+        elif comp_flag in [CompressionFlags.COMPRESSION_4, CompressionFlags.COMPRESSION_5] and os.environ.get('UNITYPY_AK'):  # ARKNIGHTS CUSTOM
+            ip = 0
+            op = 0
+            AK_LITERAL_LENGTH_MASK = ((1 << 4) - 1) & 0xFF
+            AK_MATCH_LENGTH_MASK = (~AK_LITERAL_LENGTH_MASK) & 0xFF
+            fixed_compressed_data = bytearray(compressed_data)
+            while True:
+                literal_length, match_length = (
+                    fixed_compressed_data[ip] & AK_LITERAL_LENGTH_MASK,
+                    (fixed_compressed_data[ip] & AK_MATCH_LENGTH_MASK) >> 4 & 0xff,
+                )
+                fixed_compressed_data[ip] = (literal_length << 4 | match_length) & 0xFF
+                ip += 1
+                if literal_length == 15:
+                    l, ip = BundleFile.read_long_length_no_check(fixed_compressed_data, ip)
+                    literal_length += l
+                op += literal_length
+                ip += literal_length
+                if uncompressed_size == op:  # MFLIMIT end of block
+                    break
+                offset = fixed_compressed_data[ip + 1] | fixed_compressed_data[ip] << 8
+                fixed_compressed_data[ip] = offset & 0xFF
+                fixed_compressed_data[ip + 1] = (offset >> 8) & 0xFF
+                ip += 2
+                if match_length == 15:
+                    m, ip = BundleFile.read_long_length_no_check(fixed_compressed_data, ip)
+                    match_length += m
+                match_length += 4  # MINMATCH
+                op += match_length
+            return CompressionHelper.decompress_lz4(bytes(fixed_compressed_data), uncompressed_size)
         else:
             return compressed_data
 
diff --git a/tests/samples/a1dd7f06fc870d5df6ccb483c7cd5686.bin b/tests/samples/a1dd7f06fc870d5df6ccb483c7cd5686.bin
new file mode 100644
index 00000000..4b4c4d41
Binary files /dev/null and b/tests/samples/a1dd7f06fc870d5df6ccb483c7cd5686.bin differ
diff --git a/tests/test_ak.py b/tests/test_ak.py
new file mode 100644
index 00000000..38201472
--- /dev/null
+++ b/tests/test_ak.py
@@ -0,0 +1,29 @@
+import os
+from tempfile import TemporaryDirectory
+
+from UnityPy.tools.extractor import extract_assets
+
+SAMPLES = os.path.join(os.path.dirname(os.path.abspath(__file__)), "samples")
+
+
+def test_ak():
+    os.environ['UNITYPY_AK'] = '1'
+    
+    temp_dir = TemporaryDirectory(prefix="unitypy_test_ak")
+    extract_assets(
+        SAMPLES,
+        temp_dir.name,
+        True,
+    )
+    files = [
+        os.path.relpath(os.path.join(root, f), temp_dir.name)
+        for root, dirs, files in os.walk(temp_dir.name)
+        for f in files
+    ]
+    print(files)
+    temp_dir.cleanup()
+    assert len(files) == 46
+
+
+if __name__ == "__main__":
+    test_ak()