diff --git a/client/src/main/java/com/theokanning/openai/client/OpenAiApi.java b/client/src/main/java/com/theokanning/openai/client/OpenAiApi.java
index 7342e953..611cbf01 100644
--- a/client/src/main/java/com/theokanning/openai/client/OpenAiApi.java
+++ b/client/src/main/java/com/theokanning/openai/client/OpenAiApi.java
@@ -199,126 +199,126 @@ public interface OpenAiApi {
     @GET("v1/dashboard/billing/usage")
     Single<BillingUsage> billingUsage(@Query("start_date") LocalDate starDate, @Query("end_date") LocalDate endDate);
     
-    @Headers({"OpenAI-Beta: assistants=v1"})
+    @Headers({"OpenAI-Beta: assistants=v1", "Content-Type: application/json"})
     @POST("/v1/assistants")
     Single<Assistant> createAssistant(@Body AssistantRequest request);
 
-    @Headers({"OpenAI-Beta: assistants=v1"})
+    @Headers({"OpenAI-Beta: assistants=v1", "Content-Type: application/json"})
     @GET("/v1/assistants/{assistant_id}")
     Single<Assistant> retrieveAssistant(@Path("assistant_id") String assistantId);
 
-    @Headers({"OpenAI-Beta: assistants=v1"})
+    @Headers({"OpenAI-Beta: assistants=v1", "Content-Type: application/json"})
     @POST("/v1/assistants/{assistant_id}")
     Single<Assistant> modifyAssistant(@Path("assistant_id") String assistantId, @Body ModifyAssistantRequest request);
 
-    @Headers({"OpenAI-Beta: assistants=v1"})
+    @Headers({"OpenAI-Beta: assistants=v1", "Content-Type: application/json"})
     @DELETE("/v1/assistants/{assistant_id}")
     Single<DeleteResult> deleteAssistant(@Path("assistant_id") String assistantId);
 
-    @Headers({"OpenAI-Beta: assistants=v1"})
+    @Headers({"OpenAI-Beta: assistants=v1", "Content-Type: application/json"})
     @GET("/v1/assistants")
     Single<OpenAiResponse<Assistant>> listAssistants(@QueryMap Map<String, Object> filterRequest);
 
-    @Headers({"OpenAI-Beta: assistants=v1"})
+    @Headers({"OpenAI-Beta: assistants=v1", "Content-Type: application/json"})
     @POST("/v1/assistants/{assistant_id}/files")
     Single<AssistantFile> createAssistantFile(@Path("assistant_id") String assistantId, @Body AssistantFileRequest fileRequest);
 
-    @Headers({"OpenAI-Beta: assistants=v1"})
+    @Headers({"OpenAI-Beta: assistants=v1", "Content-Type: application/json"})
     @GET("/v1/assistants/{assistant_id}/files/{file_id}")
     Single<AssistantFile> retrieveAssistantFile(@Path("assistant_id") String assistantId, @Path("file_id") String fileId);
 
-    @Headers({"OpenAI-Beta: assistants=v1"})
+    @Headers({"OpenAI-Beta: assistants=v1", "Content-Type: application/json"})
     @DELETE("/v1/assistants/{assistant_id}/files/{file_id}")
     Single<DeleteResult> deleteAssistantFile(@Path("assistant_id") String assistantId, @Path("file_id") String fileId);
 
-    @Headers({"OpenAI-Beta: assistants=v1"})
+    @Headers({"OpenAI-Beta: assistants=v1", "Content-Type: application/json"})
     @GET("/v1/assistants/{assistant_id}/files")
     Single<OpenAiResponse<AssistantFile>> listAssistantFiles(@Path("assistant_id") String assistantId, @QueryMap Map<String, Object> filterRequest);
 
-    @Headers({"OpenAI-Beta: assistants=v1"})
+    @Headers({"OpenAI-Beta: assistants=v1", "Content-Type: application/json"})
     @POST("/v1/threads")
     Single<Thread> createThread(@Body ThreadRequest request);
 
-    @Headers({"OpenAI-Beta: assistants=v1"})
+    @Headers({"OpenAI-Beta: assistants=v1", "Content-Type: application/json"})
     @GET("/v1/threads/{thread_id}")
     Single<Thread> retrieveThread(@Path("thread_id") String threadId);
 
-    @Headers({"OpenAI-Beta: assistants=v1"})
+    @Headers({"OpenAI-Beta: assistants=v1", "Content-Type: application/json"})
     @POST("/v1/threads/{thread_id}")
     Single<Thread> modifyThread(@Path("thread_id") String threadId, @Body ThreadRequest request);
 
-    @Headers({"OpenAI-Beta: assistants=v1"})
+    @Headers({"OpenAI-Beta: assistants=v1", "Content-Type: application/json"})
     @DELETE("/v1/threads/{thread_id}")
     Single<DeleteResult> deleteThread(@Path("thread_id") String threadId);
 
 
-    @Headers({"OpenAI-Beta: assistants=v1"})
+    @Headers({"OpenAI-Beta: assistants=v1", "Content-Type: application/json"})
     @POST("/v1/threads/{thread_id}/messages")
     Single<Message> createMessage(@Path("thread_id") String threadId, @Body MessageRequest request);
 
-    @Headers({"OpenAI-Beta: assistants=v1"})
+    @Headers({"OpenAI-Beta: assistants=v1", "Content-Type: application/json"})
     @GET("/v1/threads/{thread_id}/messages/{message_id}")
     Single<Message> retrieveMessage(@Path("thread_id") String threadId, @Path("message_id") String messageId);
 
-    @Headers({"OpenAI-Beta: assistants=v1"})
+    @Headers({"OpenAI-Beta: assistants=v1", "Content-Type: application/json"})
     @POST("/v1/threads/{thread_id}/messages/{message_id}")
     Single<Message> modifyMessage(@Path("thread_id") String threadId, @Path("message_id") String messageId, @Body ModifyMessageRequest request);
 
-    @Headers({"OpenAI-Beta: assistants=v1"})
+    @Headers({"OpenAI-Beta: assistants=v1", "Content-Type: application/json"})
     @GET("/v1/threads/{thread_id}/messages")
     Single<OpenAiResponse<Message>> listMessages(@Path("thread_id") String threadId);
 
-    @Headers({"OpenAI-Beta: assistants=v1"})
+    @Headers({"OpenAI-Beta: assistants=v1", "Content-Type: application/json"})
     @GET("/v1/threads/{thread_id}/messages")
     Single<OpenAiResponse<Message>> listMessages(@Path("thread_id") String threadId, @QueryMap Map<String, Object> filterRequest);
 
-    @Headers({"OpenAI-Beta: assistants=v1"})
+    @Headers({"OpenAI-Beta: assistants=v1", "Content-Type: application/json"})
     @GET("/v1/threads/{thread_id}/messages/{message_id}/files/{file_id}")
     Single<MessageFile> retrieveMessageFile(@Path("thread_id") String threadId, @Path("message_id") String messageId, @Path("file_id") String fileId);
 
-    @Headers({"OpenAI-Beta: assistants=v1"})
+    @Headers({"OpenAI-Beta: assistants=v1", "Content-Type: application/json"})
     @GET("/v1/threads/{thread_id}/messages/{message_id}/files")
     Single<OpenAiResponse<MessageFile>> listMessageFiles(@Path("thread_id") String threadId, @Path("message_id") String messageId);
 
-    @Headers({"OpenAI-Beta: assistants=v1"})
+    @Headers({"OpenAI-Beta: assistants=v1", "Content-Type: application/json"})
     @GET("/v1/threads/{thread_id}/messages/{message_id}/files")
     Single<OpenAiResponse<MessageFile>> listMessageFiles(@Path("thread_id") String threadId, @Path("message_id") String messageId, @QueryMap Map<String, Object> filterRequest);
 
-    @Headers("OpenAI-Beta: assistants=v1")
+    @Headers({"OpenAI-Beta: assistants=v1", "Content-Type: application/json"})
     @POST("/v1/threads/{thread_id}/runs")
     Single<Run> createRun(@Path("thread_id") String threadId, @Body RunCreateRequest runCreateRequest);
 
-    @Headers("OpenAI-Beta: assistants=v1")
+    @Headers({"OpenAI-Beta: assistants=v1", "Content-Type: application/json"})
     @GET("/v1/threads/{thread_id}/runs/{run_id}")
     Single<Run> retrieveRun(@Path("thread_id") String threadId, @Path("run_id") String runId);
 
-    @Headers("OpenAI-Beta: assistants=v1")
+    @Headers({"OpenAI-Beta: assistants=v1", "Content-Type: application/json"})
     @POST("/v1/threads/{thread_id}/runs/{run_id}")
     Single<Run> modifyRun(@Path("thread_id") String threadId, @Path("run_id") String runId, @Body Map<String, String> metadata);
 
-    @Headers("OpenAI-Beta: assistants=v1")
+    @Headers({"OpenAI-Beta: assistants=v1", "Content-Type: application/json"})
     @GET("/v1/threads/{thread_id}/runs")
     Single<OpenAiResponse<Run>> listRuns(@Path("thread_id") String threadId, @QueryMap Map<String, String> listSearchParameters);
 
 
-    @Headers("OpenAI-Beta: assistants=v1")
+    @Headers({"OpenAI-Beta: assistants=v1", "Content-Type: application/json"})
     @POST("/v1/threads/{thread_id}/runs/{run_id}/submit_tool_outputs")
     Single<Run> submitToolOutputs(@Path("thread_id") String threadId, @Path("run_id") String runId, @Body SubmitToolOutputsRequest submitToolOutputsRequest);
 
 
-    @Headers("OpenAI-Beta: assistants=v1")
+    @Headers({"OpenAI-Beta: assistants=v1", "Content-Type: application/json"})
     @POST("/v1/threads/{thread_id}/runs/{run_id}/cancel")
     Single<Run> cancelRun(@Path("thread_id") String threadId, @Path("run_id") String runId);
     
-    @Headers("OpenAI-Beta: assistants=v1")
+    @Headers({"OpenAI-Beta: assistants=v1", "Content-Type: application/json"})
     @POST("/v1/threads/runs")
     Single<Run> createThreadAndRun(@Body CreateThreadAndRunRequest createThreadAndRunRequest);
 
-    @Headers("OpenAI-Beta: assistants=v1")
+    @Headers({"OpenAI-Beta: assistants=v1", "Content-Type: application/json"})
     @GET("/v1/threads/{thread_id}/runs/{run_id}/steps/{step_id}")
     Single<RunStep> retrieveRunStep(@Path("thread_id") String threadId, @Path("run_id") String runId, @Path("step_id") String stepId);
 
-    @Headers("OpenAI-Beta: assistants=v1")
+    @Headers({"OpenAI-Beta: assistants=v1", "Content-Type: application/json"})
     @GET("/v1/threads/{thread_id}/runs/{run_id}/steps")
     Single<OpenAiResponse<RunStep>> listRunSteps(@Path("thread_id") String threadId, @Path("run_id") String runId, @QueryMap Map<String, String> listSearchParameters);
 }