upgrade guide

website/content/en/highlights/2023-09-26-0-33-0-upgrade-guide.md

@@ -18,11 +18,12 @@ and **deprecations**:
 
 1. [Default config location change](#default-config-location-change)
 1. [Renaming the `armv7` rpm package](#armv7-rename)
-2. [Metadata field in the Vector protobuf definition](#vector-proto-metadata)
+1. [Metadata field in the Vector protobuf definition](#vector-proto-metadata)
 
 and **potentially impactful changes**:
 
 1. [Async runtime default number of worker threads](#runtime-worker-threads)
+1. [Setting `request.concurrency = "none"`](#request-concurrency)
 
 We cover them below to help you upgrade quickly:
 
@@ -91,3 +92,11 @@ has limited quotas, but note this change may impact performance.
 
 The number of worker threads used can be seen by enabling debug logging, and the value can
 be overriden by setting the `VECTOR_THREADS` environment variable.
+
+#### Setting `request.concurrency = "none"` {#request-concurrency}
+
+Explicitly setting `request.concurrency = "none"` in a sink configuration now properly configures
+the sink to have a fixed concurrency limit of 1, as was stated in the documentation. Previously, the
+above configuration would result in the sink using adaptive request concurrency. The default setting
+remains to be adaptive request concurrency.
+