diff --git a/CHANGELOG.md b/CHANGELOG.md
index c9a150375..3a312d891 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -4,6 +4,10 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+## [3.9.3]
+### Fixed
+- Reduced `start-execution-worker` concurrency to address AWS Batch `Too Many Requests` errors. Fixes [#1676](https://github.com/ASFHyP3/hyp3/issues/1676).
+
 ## [3.9.2]
 ### Fixed
 - Reverted `asf_search` to v6.0.2. Fixes [#1673](https://github.com/ASFHyP3/hyp3/issues/1673).
diff --git a/apps/start-execution-manager/src/start_execution_manager.py b/apps/start-execution-manager/src/start_execution_manager.py
index 143810b2f..ef13b6f8f 100644
--- a/apps/start-execution-manager/src/start_execution_manager.py
+++ b/apps/start-execution-manager/src/start_execution_manager.py
@@ -28,7 +28,7 @@ def lambda_handler(event, context) -> None:
     pending_jobs = dynamo.jobs.get_jobs_waiting_for_execution(limit=900)
     logger.info(f'Got {len(pending_jobs)} pending jobs')
 
-    batch_size = 300
+    batch_size = 450
     for i in range(0, len(pending_jobs), batch_size):
         jobs = pending_jobs[i:i + batch_size]
         logger.info(f'Invoking worker for {len(jobs)} jobs')
diff --git a/tests/test_start_execution_manager.py b/tests/test_start_execution_manager.py
index b61d10ebc..ed6ddadff 100644
--- a/tests/test_start_execution_manager.py
+++ b/tests/test_start_execution_manager.py
@@ -67,17 +67,16 @@ def test_lambda_handler_900_jobs():
         mock_get_jobs_waiting_for_execution.assert_called_once_with(limit=900)
 
         assert mock_invoke_worker.mock_calls == [
-            call('test-worker-function-arn', mock_jobs[0:300]),
-            call('test-worker-function-arn', mock_jobs[300:600]),
-            call('test-worker-function-arn', mock_jobs[600:900]),
+            call('test-worker-function-arn', mock_jobs[0:450]),
+            call('test-worker-function-arn', mock_jobs[450:900]),
         ]
 
 
-def test_lambda_handler_400_jobs():
+def test_lambda_handler_500_jobs():
     with patch('dynamo.jobs.get_jobs_waiting_for_execution') as mock_get_jobs_waiting_for_execution, \
             patch('start_execution_manager.invoke_worker') as mock_invoke_worker, \
             patch.dict(os.environ, {'START_EXECUTION_WORKER_ARN': 'test-worker-function-arn'}, clear=True):
-        mock_jobs = list(range(400))
+        mock_jobs = list(range(500))
         mock_get_jobs_waiting_for_execution.return_value = mock_jobs
 
         mock_invoke_worker.return_value = {'StatusCode': None}
@@ -87,8 +86,8 @@ def test_lambda_handler_400_jobs():
         mock_get_jobs_waiting_for_execution.assert_called_once_with(limit=900)
 
         assert mock_invoke_worker.mock_calls == [
-            call('test-worker-function-arn', mock_jobs[0:300]),
-            call('test-worker-function-arn', mock_jobs[300:400]),
+            call('test-worker-function-arn', mock_jobs[0:450]),
+            call('test-worker-function-arn', mock_jobs[450:500]),
         ]