diff --git a/awscrt/s3.py b/awscrt/s3.py
index 2a732f5ff..c77f32c81 100644
--- a/awscrt/s3.py
+++ b/awscrt/s3.py
@@ -185,10 +185,19 @@ class S3FileIoOptions:
     direct_io: bool = False
     """
     Enable direct IO to bypass the OS cache. Helpful when the disk I/O outperforms the kernel cache.
-    Notes:
-    - Only supported on linux for now.
-    - Only supports upload for now.
+
+    - Currently only Linux supports direct I/O. On unsupported platforms, the request transparently
+      falls back to buffered I/O and a warning is logged.
+    - Supported for both upload (send_filepath) and download (recv_filepath).
+    - For upload, part_size MUST be page-aligned when direct_io is enabled (hard fail otherwise).
+      The client controls part_size and is responsible for ensuring alignment.
+    - For download, this is a best-effort optimization. The request transparently falls back to
+      buffered I/O (logging a warning) if any of the following preconditions are not met:
+      part_size is not page-aligned, recv_file_position is not page-aligned (WRITE_TO_POSITION),
+      existing file size is not page-aligned (CREATE_OR_APPEND), or the last part has an
+      unaligned length (only that part falls back).
     - Check NOTES for O_DIRECT for additional info https://man7.org/linux/man-pages/man2/openat.2.html
+
     In summary, O_DIRECT is a potentially powerful tool that should be used with caution.
     """
 
diff --git a/crt/aws-c-common b/crt/aws-c-common
index 48dd6cdff..2b4c620fe 160000
--- a/crt/aws-c-common
+++ b/crt/aws-c-common
@@ -1 +1 @@
-Subproject commit 48dd6cdff7bac0005a9c6b49c15a0765622c0e70
+Subproject commit 2b4c620fecec43fb847da3d2064ce023ebfd3ef9
diff --git a/crt/aws-c-s3 b/crt/aws-c-s3
index dd71b3be7..9bcccf21b 160000
--- a/crt/aws-c-s3
+++ b/crt/aws-c-s3
@@ -1 +1 @@
-Subproject commit dd71b3be7d2545d1470cd20464742fef297d50d3
+Subproject commit 9bcccf21bbbef08fda20efacb50b8a180e63f0ac
diff --git a/crt/aws-c-sdkutils b/crt/aws-c-sdkutils
index f678bda9e..727df06fc 160000
--- a/crt/aws-c-sdkutils
+++ b/crt/aws-c-sdkutils
@@ -1 +1 @@
-Subproject commit f678bda9e21f7217e4bbf35e0d1ea59540687933
+Subproject commit 727df06fc0e998e673de70fb69e5a634fe4979bc
diff --git a/crt/aws-lc b/crt/aws-lc
index 44766fa7d..6f246af4c 160000
--- a/crt/aws-lc
+++ b/crt/aws-lc
@@ -1 +1 @@
-Subproject commit 44766fa7daa88e5afc7fc6de3311c48eeeb02f39
+Subproject commit 6f246af4cd1de8cee8c62d76139bcda299c1aa00