diff --git a/ldclient/config.py b/ldclient/config.py
index 32b28dfc..fbc88ac8 100644
--- a/ldclient/config.py
+++ b/ldclient/config.py
@@ -9,7 +9,11 @@
 
 from ldclient.feature_store import InMemoryFeatureStore
 from ldclient.hook import Hook
-from ldclient.impl.util import log, validate_application_info
+from ldclient.impl.util import (
+    log,
+    validate_application_info,
+    validate_sdk_key_format
+)
 from ldclient.interfaces import (
     BigSegmentStore,
     DataSourceUpdateSink,
@@ -261,7 +265,7 @@ def __init__(
         :param omit_anonymous_contexts: Sets whether anonymous contexts should be omitted from index and identify events.
         :param payload_filter_key: The payload filter is used to selectively limited the flags and segments delivered in the data source payload.
         """
-        self.__sdk_key = sdk_key
+        self.__sdk_key = validate_sdk_key_format(sdk_key, log)
 
         self.__base_uri = base_uri.rstrip('/')
         self.__events_uri = events_uri.rstrip('/')
@@ -302,6 +306,7 @@ def __init__(
 
     def copy_with_new_sdk_key(self, new_sdk_key: str) -> 'Config':
         """Returns a new ``Config`` instance that is the same as this one, except for having a different SDK key.
+        The key will not be updated if the provided key contains invalid characters.
 
         :param new_sdk_key: the new SDK key
         """
@@ -542,8 +547,8 @@ def data_source_update_sink(self) -> Optional[DataSourceUpdateSink]:
         return self._data_source_update_sink
 
     def _validate(self):
-        if self.offline is False and self.sdk_key is None or self.sdk_key == '':
-            log.warning("Missing or blank sdk_key.")
+        if self.offline is False and self.sdk_key == '':
+            log.warning("Missing or blank SDK key")
 
 
 __all__ = ['Config', 'BigSegmentsConfig', 'HTTPConfig']
diff --git a/ldclient/impl/util.py b/ldclient/impl/util.py
index 4fbaf110..e60feb9d 100644
--- a/ldclient/impl/util.py
+++ b/ldclient/impl/util.py
@@ -27,8 +27,13 @@ def timedelta_millis(delta: timedelta) -> float:
 
 __BASE_TYPES__ = (str, float, int, bool)
 
+# Maximum length for SDK keys
+_MAX_SDK_KEY_LENGTH = 8192
 
-_retryable_statuses = [400, 408, 429]
+_RETRYABLE_STATUSES = [400, 408, 429]
+
+# Compiled regex pattern for valid characters in application values and SDK keys
+_VALID_CHARACTERS_REGEX = re.compile(r"[^a-zA-Z0-9._-]")
 
 
 def validate_application_info(application: dict, logger: logging.Logger) -> dict:
@@ -46,13 +51,35 @@ def validate_application_value(value: Any, name: str, logger: logging.Logger) ->
         logger.warning('Value of application[%s] was longer than 64 characters and was discarded' % name)
         return ""
 
-    if re.search(r"[^a-zA-Z0-9._-]", value):
+    if _VALID_CHARACTERS_REGEX.search(value):
         logger.warning('Value of application[%s] contained invalid characters and was discarded' % name)
         return ""
 
     return value
 
 
+def validate_sdk_key_format(sdk_key: str, logger: logging.Logger) -> str:
+    """
+    Validates that an SDK key does not contain invalid characters and is not too long for our systems.
+
+    :param sdk_key: the SDK key to validate
+    :param logger: the logger to use for logging warnings
+    :return: the validated SDK key, or empty string if the SDK key is invalid
+    """
+    if sdk_key is None or sdk_key == '':
+        return ""
+
+    if not isinstance(sdk_key, str):
+        return ""
+    if len(sdk_key) > _MAX_SDK_KEY_LENGTH:
+        logger.warning('SDK key was longer than %d characters and was discarded' % _MAX_SDK_KEY_LENGTH)
+        return ""
+    if _VALID_CHARACTERS_REGEX.search(sdk_key):
+        logger.warning('SDK key contained invalid characters and was discarded')
+        return ""
+    return sdk_key
+
+
 def _headers(config):
     base_headers = _base_headers(config)
     base_headers.update({'Content-Type': "application/json"})
@@ -106,7 +133,7 @@ def throw_if_unsuccessful_response(resp):
 
 def is_http_error_recoverable(status):
     if status >= 400 and status < 500:
-        return status in _retryable_statuses  # all other 4xx besides these are unrecoverable
+        return status in _RETRYABLE_STATUSES  # all other 4xx besides these are unrecoverable
     return True  # all other errors are recoverable
 
 
diff --git a/ldclient/testing/impl/test_util.py b/ldclient/testing/impl/test_util.py
new file mode 100644
index 00000000..ea843e4b
--- /dev/null
+++ b/ldclient/testing/impl/test_util.py
@@ -0,0 +1,65 @@
+import logging
+
+from ldclient.impl.util import validate_sdk_key_format
+
+
+def test_validate_sdk_key_format_valid():
+    """Test validation of valid SDK keys"""
+    logger = logging.getLogger('test')
+    valid_keys = [
+        "sdk-12345678-1234-1234-1234-123456789012",
+        "valid-sdk-key-123",
+        "VALID_SDK_KEY_456",
+        "test.key_with.dots",
+        "test-key-with-hyphens"
+    ]
+
+    for key in valid_keys:
+        result = validate_sdk_key_format(key, logger)
+        assert result == key  # Should return the same key if valid
+
+
+def test_validate_sdk_key_format_invalid():
+    """Test validation of invalid SDK keys"""
+    logger = logging.getLogger('test')
+    invalid_keys = [
+        "sdk-key-with-\x00-null",
+        "sdk-key-with-\n-newline",
+        "sdk-key-with-\t-tab",
+        "sdk key with spaces",
+        "sdk@key#with$special%chars",
+        "sdk/key\\with/slashes"
+    ]
+
+    for key in invalid_keys:
+        result = validate_sdk_key_format(key, logger)
+        assert result == ''  # Should return empty string for invalid keys
+
+
+def test_validate_sdk_key_format_non_string():
+    """Test validation of non-string SDK keys"""
+    logger = logging.getLogger('test')
+    non_string_values = [123, object(), [], {}]
+
+    for value in non_string_values:
+        result = validate_sdk_key_format(value, logger)
+        assert result == ''  # Should return empty string for non-string values
+
+
+def test_validate_sdk_key_format_empty_and_none():
+    """Test validation of empty and None SDK keys"""
+    logger = logging.getLogger('test')
+    assert validate_sdk_key_format("", logger) == ''  # Empty string should return empty string
+    assert validate_sdk_key_format(None, logger) == ''  # None should return empty string
+
+
+def test_validate_sdk_key_format_max_length():
+    """Test validation of SDK key maximum length"""
+    logger = logging.getLogger('test')
+    valid_key = "a" * 8192
+    result = validate_sdk_key_format(valid_key, logger)
+    assert result == valid_key  # Should return the same key if valid
+
+    invalid_key = "a" * 8193
+    result = validate_sdk_key_format(invalid_key, logger)
+    assert result == ''  # Should return empty string for keys that are too long
diff --git a/ldclient/testing/test_config.py b/ldclient/testing/test_config.py
index 77fc5b34..b5321d36 100644
--- a/ldclient/testing/test_config.py
+++ b/ldclient/testing/test_config.py
@@ -45,6 +45,71 @@ def test_trims_trailing_slashes_on_uris():
     assert config.stream_base_uri == "https://blog.launchdarkly.com"
 
 
+def test_sdk_key_validation_valid_keys():
+    """Test that valid SDK keys are accepted"""
+    valid_keys = [
+        "sdk-12345678-1234-1234-1234-123456789012",
+        "valid-sdk-key-123",
+        "VALID_SDK_KEY_456",
+        "test.key_with.dots",
+        "test-key-with-hyphens"
+    ]
+
+    for key in valid_keys:
+        config = Config(sdk_key=key)
+        assert config.sdk_key == key
+
+
+def test_sdk_key_validation_invalid_keys():
+    """Test that invalid SDK keys are not set"""
+    invalid_keys = [
+        "sdk-key-with-\x00-null",
+        "sdk-key-with-\n-newline",
+        "sdk-key-with-\t-tab",
+        "sdk key with spaces",
+        "sdk@key#with$special%chars",
+        "sdk/key\\with/slashes"
+    ]
+
+    for key in invalid_keys:
+        config = Config(sdk_key=key)
+        assert config.sdk_key == ''
+
+
+def test_sdk_key_validation_empty_key():
+    """Test that empty SDK keys are accepted"""
+    config = Config(sdk_key="")
+    assert config.sdk_key == ""
+
+
+def test_sdk_key_validation_none_key():
+    """Test that None SDK keys are accepted"""
+    config = Config(sdk_key=None)
+    assert config.sdk_key == ''
+
+
+def test_sdk_key_validation_max_length():
+    """Test SDK key maximum length validation"""
+    valid_key = "a" * 8192
+    config = Config(sdk_key=valid_key)
+    assert config.sdk_key == valid_key
+
+    invalid_key = "a" * 8193
+    config = Config(sdk_key=invalid_key)
+    assert config.sdk_key == ''
+
+
+def test_copy_with_new_sdk_key_validation():
+    """Test that copy_with_new_sdk_key validates the new key"""
+    original_config = Config(sdk_key="valid-key")
+
+    new_config = original_config.copy_with_new_sdk_key("another-valid-key")
+    assert new_config.sdk_key == "another-valid-key"
+
+    invalid_config = original_config.copy_with_new_sdk_key("invalid key with spaces")
+    assert invalid_config.sdk_key == ''
+
+
 def application_can_be_set_and_read():
     application = {"id": "my-id", "version": "abcdef"}
     config = Config(sdk_key="SDK_KEY", application=application)