chore: add usage field to non-streaming responses by default (#3922)

Signed-off-by: ayushag <ayushag@nvidia.com>
Co-authored-by: Ryan McCormick <rmccormick@nvidia.com>

lib/llm/src/preprocessor.rs

@@ -818,6 +818,7 @@ impl
 
         // Preserve original inbound streaming flag before any internal overrides
         let request_id = context.id().to_string();
+        let original_stream_flag = request.inner.stream.unwrap_or(false);
 
         // Build audit handle (None if DYN_AUDIT_ENABLED=0)
         let mut audit_handle = crate::audit::handle::create_handle(&request, &request_id);
@@ -826,6 +827,11 @@ impl
             h.set_request(std::sync::Arc::new(request.clone()));
         }
 
+        // For non-streaming requests (stream=false), enable usage by default
+        // This ensures compliance with OpenAI API spec where non-streaming responses
+        // always include usage statistics
+        request.enable_usage_for_nonstreaming(original_stream_flag);
+
         // Set stream=true for internal processing (after audit capture)
         request.inner.stream = Some(true);
 
@@ -952,6 +958,14 @@ impl
         // unpack the request
         let (mut request, context) = request.into_parts();
 
+        // Preserve original streaming flag
+        let original_stream_flag = request.inner.stream.unwrap_or(false);
+
+        // For non-streaming requests (stream=false), enable usage by default
+        // This ensures compliance with OpenAI API spec where non-streaming responses
+        // always include usage statistics
+        request.enable_usage_for_nonstreaming(original_stream_flag);
+
         request.inner.stream = Some(true);
 
         // create a response generator

lib/llm/src/protocols/openai/chat_completions/delta.rs

@@ -10,6 +10,29 @@ use crate::{
 
 /// Provides a method for generating a [`DeltaGenerator`] from a chat completion request.
 impl NvCreateChatCompletionRequest {
+    /// Enables usage tracking for non-streaming requests to comply with OpenAI API specification.
+    ///
+    /// According to OpenAI API spec, non-streaming chat completion responses (stream=false)
+    /// must always include usage statistics. This method ensures `stream_options.include_usage`
+    /// is set to `true` for non-streaming requests.
+    ///
+    /// # Arguments
+    /// * `original_stream_flag` - The original value of the `stream` field before any internal processing
+    pub fn enable_usage_for_nonstreaming(&mut self, original_stream_flag: bool) {
+        if !original_stream_flag {
+            // For non-streaming requests (stream=false), enable usage by default
+            if self.inner.stream_options.is_none() {
+                self.inner.stream_options =
+                    Some(dynamo_async_openai::types::ChatCompletionStreamOptions {
+                        include_usage: true,
+                    });
+            } else if let Some(ref mut opts) = self.inner.stream_options {
+                // If stream_options exists, ensure include_usage is true for non-streaming
+                opts.include_usage = true;
+            }
+        }
+    }
+
     /// Creates a [`DeltaGenerator`] instance based on the chat completion request.
     ///
     /// # Arguments
@@ -342,3 +365,66 @@ impl crate::protocols::openai::DeltaGeneratorExt<NvCreateChatCompletionStreamRes
         DeltaGenerator::is_usage_enabled(self)
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use dynamo_async_openai::types::{
+        ChatCompletionRequestMessage, ChatCompletionRequestUserMessage,
+        ChatCompletionRequestUserMessageContent, CreateChatCompletionRequest,
+    };
+
+    fn create_test_request() -> NvCreateChatCompletionRequest {
+        let messages = vec![ChatCompletionRequestMessage::User(
+            ChatCompletionRequestUserMessage {
+                content: ChatCompletionRequestUserMessageContent::Text("test".to_string()),
+                name: None,
+            },
+        )];
+
+        NvCreateChatCompletionRequest {
+            inner: CreateChatCompletionRequest {
+                model: "test-model".to_string(),
+                messages,
+                stream: Some(false),
+                stream_options: None,
+                ..Default::default()
+            },
+            common: Default::default(),
+            nvext: None,
+            chat_template_args: None,
+        }
+    }
+
+    #[test]
+    fn test_enable_usage_for_nonstreaming_enables_usage() {
+        // Test that non-streaming requests get usage enabled
+        let mut request = create_test_request();
+        assert!(request.inner.stream_options.is_none());
+
+        request.enable_usage_for_nonstreaming(false); // false = non-streaming
+
+        assert!(
+            request.inner.stream_options.is_some(),
+            "Non-streaming request should have stream_options created"
+        );
+        assert!(
+            request.inner.stream_options.unwrap().include_usage,
+            "Non-streaming request should have include_usage=true for OpenAI compliance"
+        );
+    }
+
+    #[test]
+    fn test_enable_usage_for_nonstreaming_ignores_streaming() {
+        // Test that streaming requests are not modified
+        let mut request = create_test_request();
+        assert!(request.inner.stream_options.is_none());
+
+        request.enable_usage_for_nonstreaming(true); // true = streaming
+
+        assert!(
+            request.inner.stream_options.is_none(),
+            "Streaming request should not have stream_options modified"
+        );
+    }
+}

lib/llm/src/protocols/openai/completions/delta.rs

@@ -5,6 +5,31 @@ use super::{NvCreateCompletionRequest, NvCreateCompletionResponse};
 use crate::{protocols::common, types::TokenIdType};
 
 impl NvCreateCompletionRequest {
+    /// Enables usage tracking for non-streaming requests to comply with OpenAI API specification.
+    ///
+    /// According to OpenAI API spec, non-streaming completion responses (stream=false)
+    /// must always include usage statistics. This method ensures `stream_options.include_usage`
+    /// is set to `true` for non-streaming requests.
+    ///
+    /// Reference: https://platform.openai.com/docs/api-reference/completions/create
+    ///
+    /// # Arguments
+    /// * `original_stream_flag` - The original value of the `stream` field before any internal processing
+    pub fn enable_usage_for_nonstreaming(&mut self, original_stream_flag: bool) {
+        if !original_stream_flag {
+            // For non-streaming requests (stream=false), enable usage by default
+            if self.inner.stream_options.is_none() {
+                self.inner.stream_options =
+                    Some(dynamo_async_openai::types::ChatCompletionStreamOptions {
+                        include_usage: true,
+                    });
+            } else if let Some(ref mut opts) = self.inner.stream_options {
+                // If stream_options exists, ensure include_usage is true for non-streaming
+                opts.include_usage = true;
+            }
+        }
+    }
+
     // put this method on the request
     // inspect the request to extract options
     pub fn response_generator(&self, request_id: String) -> DeltaGenerator {

lib/llm/tests/test_streaming_usage.rs

@@ -9,7 +9,10 @@ use dynamo_async_openai::types::{
 };
 use dynamo_llm::preprocessor::OpenAIPreprocessor;
 use dynamo_llm::protocols::common::llm_backend::{BackendOutput, FinishReason};
-use dynamo_llm::protocols::openai::chat_completions::NvCreateChatCompletionRequest;
+use dynamo_llm::protocols::openai::ParsingOptions;
+use dynamo_llm::protocols::openai::chat_completions::{
+    NvCreateChatCompletionRequest, aggregator::ChatCompletionAggregator,
+};
 use dynamo_runtime::engine::{AsyncEngineContext, AsyncEngineStream};
 use dynamo_runtime::protocols::annotated::Annotated;
 use futures::StreamExt;
@@ -303,3 +306,99 @@ async fn test_streaming_with_usage_false() {
         }
     }
 }
+
+/// Helper to create a non-streaming chat completion request
+fn create_nonstreaming_chat_request() -> NvCreateChatCompletionRequest {
+    let messages = vec![ChatCompletionRequestMessage::User(
+        ChatCompletionRequestUserMessage {
+            content: ChatCompletionRequestUserMessageContent::Text("Hello".to_string()),
+            name: None,
+        },
+    )];
+
+    let inner = CreateChatCompletionRequest {
+        model: "test-model".to_string(),
+        messages,
+        stream: Some(false),
+        stream_options: None,
+        ..Default::default()
+    };
+
+    NvCreateChatCompletionRequest {
+        inner,
+        common: Default::default(),
+        nvext: None,
+        chat_template_args: None,
+    }
+}
+
+#[tokio::test]
+async fn test_nonstreaming_has_usage_field() {
+    let mut request = create_nonstreaming_chat_request();
+    assert_eq!(
+        request.inner.stream,
+        Some(false),
+        "Request should be non-streaming"
+    );
+    assert!(
+        request.inner.stream_options.is_none(),
+        "stream_options should not be set initially"
+    );
+
+    // Simulate what the preprocessor does for non-streaming requests
+    let original_stream_flag = request.inner.stream.unwrap_or(false);
+
+    // Enable usage for non-streaming requests
+    request.enable_usage_for_nonstreaming(original_stream_flag);
+
+    let request_id = "test-nonstream-123".to_string();
+    let response_generator = Box::new(request.response_generator(request_id));
+
+    // Create mock backend stream
+    let ctx = Arc::new(MockContext::new());
+    let backend_stream = create_mock_backend_stream(ctx.clone());
+
+    // Transform the stream (this generates streaming chunks)
+    let transformed_stream = OpenAIPreprocessor::transform_postprocessor_stream(
+        backend_stream,
+        response_generator,
+        ctx.clone(),
+    );
+
+    // Aggregate the streaming chunks into a single non-streaming response
+    // This simulates what the HTTP service does for non-streaming requests
+    let result = dynamo_async_openai::types::CreateChatCompletionResponse::from_annotated_stream(
+        transformed_stream,
+        ParsingOptions::default(),
+    )
+    .await;
+
+    assert!(result.is_ok(), "Aggregation should succeed");
+    let response = result.unwrap();
+
+    assert!(
+        response.usage.is_some(),
+        "Non-streaming chat completion response MUST have a usage field populated. \
+         This is required for OpenAI API compliance."
+    );
+
+    let usage = response.usage.unwrap();
+
+    // Verify usage contains valid token counts
+    // In our mock, we generated 3 tokens (from the 3 backend outputs)
+    assert_eq!(
+        usage.completion_tokens, 3,
+        "Completion tokens should match the number of tokens generated"
+    );
+
+    assert!(
+        usage.total_tokens > 0,
+        "Total tokens should be greater than 0"
+    );
+
+    assert_eq!(
+        usage.total_tokens,
+        usage.prompt_tokens + usage.completion_tokens,
+        "Total tokens should equal prompt_tokens + completion_tokens"
+    );
+}