diff --git a/docs/reference/python_client.md b/docs/reference/python_client.md
index 9d635541d..c9e9ed735 100644
--- a/docs/reference/python_client.md
+++ b/docs/reference/python_client.md
@@ -181,6 +181,8 @@ class BestOfSequence:
 class Details:
     # Generation finish reason
     finish_reason: FinishReason
+    # Number of prompt tokens
+    prompt_tokens: int
     # Number of generated tokens
     generated_tokens: int
     # Sampling seed if sampling was activated
diff --git a/proto/generate.proto b/proto/generate.proto
index ae4caa3f9..c5b52d1dd 100644
--- a/proto/generate.proto
+++ b/proto/generate.proto
@@ -167,6 +167,8 @@ message Generation {
     bool token_is_special = 6;
     /// Complete generated text
     optional GeneratedText generated_text = 7;
+    /// Prefill tokens length
+    uint32 prefill_tokens_length = 8;
 }
 
 message FilterBatchRequest {
diff --git a/router/src/infer.rs b/router/src/infer.rs
index df20e0061..d46ab0471 100644
--- a/router/src/infer.rs
+++ b/router/src/infer.rs
@@ -189,6 +189,7 @@ impl Infer {
         // Return values
         let mut result_prefill = Vec::new();
         let mut result_tokens = Vec::new();
+        let mut result_prefill_length = 0;
         let mut result_generated_text = None;
         let mut result_start = None;
         let mut result_queued = None;
@@ -197,16 +198,22 @@ impl Infer {
         while let Some(response) = stream.next().await {
             match response? {
                 // Add prefill tokens
-                InferStreamResponse::Prefill(tokens) => {
+                InferStreamResponse::Prefill {
+                    tokens,
+                    tokens_length,
+                } => {
                     // Create Token objects
                     // We do that here instead of in the Python code as Rust for loops are faster
-                    result_prefill = tokens
-                        .ids
-                        .into_iter()
-                        .zip(tokens.logprobs.into_iter())
-                        .zip(tokens.texts.into_iter())
-                        .map(|((id, logprob), text)| PrefillToken { id, text, logprob })
-                        .collect();
+                    if let Some(tokens_val) = tokens {
+                        result_prefill = tokens_val
+                            .ids
+                            .into_iter()
+                            .zip(tokens_val.logprobs.into_iter())
+                            .zip(tokens_val.texts.into_iter())
+                            .map(|((id, logprob), text)| PrefillToken { id, text, logprob })
+                            .collect();
+                    }
+                    result_prefill_length = tokens_length;
                 }
                 // Push last token
                 InferStreamResponse::Token(token) => result_tokens.push(token),
@@ -233,6 +240,7 @@ impl Infer {
             Ok(InferResponse {
                 prefill: result_prefill,
                 tokens: result_tokens,
+                prompt_tokens: result_prefill_length,
                 generated_text,
                 queued,
                 start,
@@ -569,10 +577,13 @@ fn send_responses(
 
     let mut stopped = false;
 
-    if let Some(prefill_tokens) = generation.prefill_tokens {
+    if generation.prefill_tokens_length > 0 {
         // Send message
         entry.response_tx.send_timeout(
-            Ok(InferStreamResponse::Prefill(prefill_tokens)),
+            Ok(InferStreamResponse::Prefill {
+                tokens: generation.prefill_tokens,
+                tokens_length: generation.prefill_tokens_length,
+            }),
             Duration::from_millis(10),
         )?;
     }
@@ -629,7 +640,10 @@ fn send_errors(error: ClientError, entries: &mut IntMap<u64, Entry>) {
 #[derive(Debug)]
 pub(crate) enum InferStreamResponse {
     // Optional first message
-    Prefill(PrefillTokens),
+    Prefill {
+        tokens: Option<PrefillTokens>,
+        tokens_length: u32,
+    },
     // Intermediate messages
     Token(Token),
     // Last message
@@ -645,17 +659,12 @@ pub(crate) enum InferStreamResponse {
 pub(crate) struct InferResponse {
     pub(crate) prefill: Vec<PrefillToken>,
     pub(crate) tokens: Vec<Token>,
+    pub(crate) prompt_tokens: u32,
     pub(crate) generated_text: GeneratedText,
     pub(crate) queued: Instant,
     pub(crate) start: Instant,
 }
 
-impl InferResponse {
-    pub(crate) fn prompt_tokens(&self) -> u32 {
-        self.prefill.len() as u32
-    }
-}
-
 #[derive(Debug, Error)]
 pub enum InferError {
     #[error("Request failed during generation: {0}")]
diff --git a/router/src/server.rs b/router/src/server.rs
index b6d249ea2..98d30ab9e 100644
--- a/router/src/server.rs
+++ b/router/src/server.rs
@@ -172,7 +172,7 @@ async fn generate(
     };
 
     let generated_tokens = response.generated_text.generated_tokens;
-    let prompt_tokens = response.prompt_tokens();
+    let prompt_tokens = response.prompt_tokens;
     let total_tokens = prompt_tokens + generated_tokens;
 
     // Token details
@@ -411,7 +411,9 @@ async fn generate_stream(
                             Ok(response) => {
                                 match response {
                                     // Prefill is ignored
-                                    InferStreamResponse::Prefill(_) => {}
+                                    InferStreamResponse::Prefill {
+                                        ..
+                                    } => {}
                                     // Yield event for every new token
                                     InferStreamResponse::Token(token) => {
                                         tracing::debug!(parent: &span, "Token: {:?}", token);
diff --git a/server/lorax_server/models/flash_causal_lm.py b/server/lorax_server/models/flash_causal_lm.py
index 91be95a86..e55d0ddd9 100644
--- a/server/lorax_server/models/flash_causal_lm.py
+++ b/server/lorax_server/models/flash_causal_lm.py
@@ -1198,6 +1198,7 @@ def generate_token(
                 generation = Generation(
                     request.id,
                     prefill_tokens,
+                    len(all_input_ids[:-1]) if prefill else 0,
                     next_token_id,
                     next_token_logprob,
                     next_token_text,
diff --git a/server/lorax_server/models/types.py b/server/lorax_server/models/types.py
index 90d3f55fa..f22ff7da3 100644
--- a/server/lorax_server/models/types.py
+++ b/server/lorax_server/models/types.py
@@ -75,6 +75,7 @@ def __len__(self):
 class Generation:
     request_id: int
     prefill_tokens: Optional[PrefillTokens]
+    prefill_tokens_length: int
     token_id: int
     token_logprob: float
     token_text: str
@@ -87,6 +88,7 @@ def to_pb(self) -> generate_pb2.Generation:
             prefill_tokens=self.prefill_tokens.to_pb()
             if self.prefill_tokens is not None
             else None,
+            prefill_tokens_length=self.prefill_tokens_length,
             token_id=self.token_id,
             token_logprob=self.token_logprob,
             token_text=self.token_text,