diff --git a/awscrt/s3.py b/awscrt/s3.py
index 7509d14da..7e5574641 100644
--- a/awscrt/s3.py
+++ b/awscrt/s3.py
@@ -180,6 +180,11 @@ class S3Client(NativeResource):
             Gigabits per second (Gbps) that we are trying to reach.
             You can also use `get_recommended_throughput_target_gbps()` to get recommended value for your system.
             10.0 Gbps by default (may change in future)
+
+        memory_limit (Optional[int]): Memory limit, in bytes, of how much memory
+            client can use for buffering data for requests.
+            Default values scale with target throughput and are currently
+            between 2GiB and 8GiB (may change in future)
     """
 
     __slots__ = ('shutdown_event', '_region')
@@ -195,7 +200,8 @@ def __init__(
             tls_connection_options=None,
             part_size=None,
             multipart_upload_threshold=None,
-            throughput_target_gbps=None):
+            throughput_target_gbps=None,
+            memory_limit=None):
         assert isinstance(bootstrap, ClientBootstrap) or bootstrap is None
         assert isinstance(region, str)
         assert isinstance(signing_config, AwsSigningConfig) or signing_config is None
@@ -236,6 +242,8 @@ def on_shutdown():
             multipart_upload_threshold = 0
         if throughput_target_gbps is None:
             throughput_target_gbps = 0
+        if memory_limit is None:
+            memory_limit = 0
 
         self._binding = _awscrt.s3_client_new(
             bootstrap,
@@ -248,6 +256,7 @@ def on_shutdown():
             part_size,
             multipart_upload_threshold,
             throughput_target_gbps,
+            memory_limit,
             s3_client_core)
 
     def make_request(
diff --git a/crt/aws-c-io b/crt/aws-c-io
index c9cb77747..df64f57fe 160000
--- a/crt/aws-c-io
+++ b/crt/aws-c-io
@@ -1 +1 @@
-Subproject commit c9cb77747d3fd2809cf3d9c43be7d5decc17e4b3
+Subproject commit df64f57feb63ab1a489ded86a87b756a48c46f35
diff --git a/crt/aws-c-s3 b/crt/aws-c-s3
index 83008e577..f961971f3 160000
--- a/crt/aws-c-s3
+++ b/crt/aws-c-s3
@@ -1 +1 @@
-Subproject commit 83008e577804643bc632ae4e603f36ab96219b9b
+Subproject commit f961971f3851782d40126f0597f007c73ba4ae0c
diff --git a/source/s3_client.c b/source/s3_client.c
index 0a5acb713..af2e88d53 100644
--- a/source/s3_client.c
+++ b/source/s3_client.c
@@ -249,10 +249,11 @@ PyObject *aws_py_s3_client_new(PyObject *self, PyObject *args) {
     uint64_t part_size;                  /* K */
     uint64_t multipart_upload_threshold; /* K */
     double throughput_target_gbps;       /* d */
+    uint64_t mem_limit;                  /* K */
     PyObject *py_core;                   /* O */
     if (!PyArg_ParseTuple(
             args,
-            "OOOOOs#iKKdO",
+            "OOOOOs#iKKdKO",
             &bootstrap_py,
             &signing_config_py,
             &credential_provider_py,
@@ -264,6 +265,7 @@ PyObject *aws_py_s3_client_new(PyObject *self, PyObject *args) {
             &part_size,
             &multipart_upload_threshold,
             &throughput_target_gbps,
+            &mem_limit,
             &py_core)) {
         return NULL;
     }
@@ -328,6 +330,7 @@ PyObject *aws_py_s3_client_new(PyObject *self, PyObject *args) {
         .tls_mode = tls_mode,
         .signing_config = signing_config,
         .part_size = part_size,
+        .memory_limit_in_bytes = mem_limit,
         .multipart_upload_threshold = multipart_upload_threshold,
         .tls_connection_options = tls_options,
         .throughput_target_gbps = throughput_target_gbps,
diff --git a/test/test_s3.py b/test/test_s3.py
index e3cb391a6..67e5a8c89 100644
--- a/test/test_s3.py
+++ b/test/test_s3.py
@@ -148,7 +148,7 @@ def full_path(self, filename):
         return os.path.join(self.rootdir, filename)
 
 
-def s3_client_new(secure, region, part_size=0, is_cancel_test=False):
+def s3_client_new(secure, region, part_size=0, is_cancel_test=False, mem_limit=None):
 
     if is_cancel_test:
         # for cancellation tests, make things slow, so it's less likely that
@@ -177,6 +177,7 @@ def s3_client_new(secure, region, part_size=0, is_cancel_test=False):
         signing_config=signing_config,
         tls_connection_options=tls_option,
         part_size=part_size,
+        memory_limit=mem_limit,
         throughput_target_gbps=throughput_target_gbps)
 
     return s3_client
@@ -313,10 +314,11 @@ def _test_s3_put_get_object(
             request,
             request_type,
             exception_name=None,
+            mem_limit=None,
             **kwargs,
     ):
 
-        s3_client = s3_client_new(False, self.region, 5 * MB)
+        s3_client = s3_client_new(False, self.region, 5 * MB, mem_limit=mem_limit)
         s3_request = s3_client.make_request(
             request=request,
             type=request_type,
@@ -342,6 +344,10 @@ def test_get_object(self):
         request = self._get_object_request(self.get_test_object_path)
         self._test_s3_put_get_object(request, S3RequestType.GET_OBJECT)
 
+    def test_get_object_mem_limit(self):
+        request = self._get_object_request(self.get_test_object_path)
+        self._test_s3_put_get_object(request, S3RequestType.GET_OBJECT, mem_limit=2 * GB)
+
     def test_put_object(self):
         put_body_stream = open(self.temp_put_obj_file_path, "rb")
         content_length = os.stat(self.temp_put_obj_file_path).st_size
@@ -349,6 +355,13 @@ def test_put_object(self):
         self._test_s3_put_get_object(request, S3RequestType.PUT_OBJECT)
         put_body_stream.close()
 
+    def test_put_object_mem_limit(self):
+        put_body_stream = open(self.temp_put_obj_file_path, "rb")
+        content_length = os.stat(self.temp_put_obj_file_path).st_size
+        request = self._put_object_request(put_body_stream, content_length)
+        self._test_s3_put_get_object(request, S3RequestType.PUT_OBJECT, mem_limit=2 * GB)
+        put_body_stream.close()
+
     def test_put_object_unknown_content_length(self):
         put_body_stream = open(self.temp_put_obj_file_path, "rb")
         content_length = os.stat(self.temp_put_obj_file_path).st_size