diff --git a/specification/cognitiveservices/OpenAI.Inference/models/chat.completions.tsp b/specification/cognitiveservices/OpenAI.Inference/models/chat.completions.tsp
index 5405b21497b2..503dca37c314 100644
--- a/specification/cognitiveservices/OpenAI.Inference/models/chat.completions.tsp
+++ b/specification/cognitiveservices/OpenAI.Inference/models/chat.completions.tsp
@@ -159,7 +159,6 @@ model ChatChoice {
   index: int32;
 
   #suppress "@azure-tools/typespec-azure-core/no-nullable" "The operation already returns nulls"
-  #suppress "@azure-tools/typespec-autorest/union-unsupported" "https://github.com/Azure/typespec-azure/issues/3180"
   @doc("The reason that this chat completions choice completed its generated.")
   @projectedName("json", "finish_reason")
   finishReason: CompletionsFinishReason | null;
diff --git a/specification/cognitiveservices/OpenAI.Inference/models/completions.create.tsp b/specification/cognitiveservices/OpenAI.Inference/models/completions.create.tsp
index c3f695e16ecf..dd7687a66360 100644
--- a/specification/cognitiveservices/OpenAI.Inference/models/completions.create.tsp
+++ b/specification/cognitiveservices/OpenAI.Inference/models/completions.create.tsp
@@ -195,7 +195,6 @@ model Choice {
   logprobs: CompletionsLogProbabilityModel | null;
 
   #suppress "@azure-tools/typespec-azure-core/no-nullable" "The operation already returns nulls"
-  #suppress "@azure-tools/typespec-autorest/union-unsupported" "https://github.com/Azure/typespec-azure/issues/3180"
   @doc("Reason for finishing")
   @projectedName("json", "finish_reason")
   finishReason: CompletionsFinishReason | null;
diff --git a/specification/cognitiveservices/data-plane/AzureOpenAI/inference/preview/2023-06-01-preview/generated.json b/specification/cognitiveservices/data-plane/AzureOpenAI/inference/preview/2023-06-01-preview/generated.json
index 408442988421..6a2761eb27a1 100644
--- a/specification/cognitiveservices/data-plane/AzureOpenAI/inference/preview/2023-06-01-preview/generated.json
+++ b/specification/cognitiveservices/data-plane/AzureOpenAI/inference/preview/2023-06-01-preview/generated.json
@@ -383,6 +383,8 @@
           "description": "The ordered index associated with this chat completions choice."
         },
         "finish_reason": {
+          "$ref": "#/definitions/CompletionsFinishReason",
+          "x-nullable": true,
           "x-typespec-name": "CompletionsFinishReason | null",
           "description": "The reason that this chat completions choice completed its generated.",
           "x-ms-client-name": "finishReason"
@@ -585,6 +587,8 @@
           "description": "The log probabilities model for tokens associated with this completions choice."
         },
         "finish_reason": {
+          "$ref": "#/definitions/CompletionsFinishReason",
+          "x-nullable": true,
           "x-typespec-name": "CompletionsFinishReason | null",
           "description": "Reason for finishing",
           "x-ms-client-name": "finishReason"
diff --git a/specification/cognitiveservices/data-plane/AzureOpenAI/inference/stable/2022-12-01/generated.json b/specification/cognitiveservices/data-plane/AzureOpenAI/inference/stable/2022-12-01/generated.json
index 13f6ad8e1121..2af4fbc17da8 100644
--- a/specification/cognitiveservices/data-plane/AzureOpenAI/inference/stable/2022-12-01/generated.json
+++ b/specification/cognitiveservices/data-plane/AzureOpenAI/inference/stable/2022-12-01/generated.json
@@ -238,6 +238,8 @@
           "description": "The ordered index associated with this chat completions choice."
         },
         "finish_reason": {
+          "$ref": "#/definitions/CompletionsFinishReason",
+          "x-nullable": true,
           "x-typespec-name": "CompletionsFinishReason | null",
           "description": "The reason that this chat completions choice completed its generated.",
           "x-ms-client-name": "finishReason"
@@ -440,6 +442,8 @@
           "description": "The log probabilities model for tokens associated with this completions choice."
         },
         "finish_reason": {
+          "$ref": "#/definitions/CompletionsFinishReason",
+          "x-nullable": true,
           "x-typespec-name": "CompletionsFinishReason | null",
           "description": "Reason for finishing",
           "x-ms-client-name": "finishReason"
diff --git a/specification/cognitiveservices/data-plane/AzureOpenAI/inference/stable/2023-05-15/generated.json b/specification/cognitiveservices/data-plane/AzureOpenAI/inference/stable/2023-05-15/generated.json
index 78fd2fe57232..5620fc6ac277 100644
--- a/specification/cognitiveservices/data-plane/AzureOpenAI/inference/stable/2023-05-15/generated.json
+++ b/specification/cognitiveservices/data-plane/AzureOpenAI/inference/stable/2023-05-15/generated.json
@@ -289,6 +289,8 @@
           "description": "The ordered index associated with this chat completions choice."
         },
         "finish_reason": {
+          "$ref": "#/definitions/CompletionsFinishReason",
+          "x-nullable": true,
           "x-typespec-name": "CompletionsFinishReason | null",
           "description": "The reason that this chat completions choice completed its generated.",
           "x-ms-client-name": "finishReason"
@@ -491,6 +493,8 @@
           "description": "The log probabilities model for tokens associated with this completions choice."
         },
         "finish_reason": {
+          "$ref": "#/definitions/CompletionsFinishReason",
+          "x-nullable": true,
           "x-typespec-name": "CompletionsFinishReason | null",
           "description": "Reason for finishing",
           "x-ms-client-name": "finishReason"