diff --git a/launcher/tests/bloom_560m.json b/launcher/tests/bloom_560m.json
index 17e2571e..96f89f6b 100644
--- a/launcher/tests/bloom_560m.json
+++ b/launcher/tests/bloom_560m.json
@@ -1,122 +1,142 @@
 {
+  "generated_text": ".get(\"action\");\n        if (action == null) {\n            throw new RuntimeException",
   "details": {
     "finish_reason": "length",
     "generated_tokens": 20,
+    "seed": null,
     "prefill": [
       {
         "id": 10264,
-        "logprob": null,
-        "text": "Test"
+        "text": "Test",
+        "logprob": null
       },
       {
         "id": 8821,
-        "logprob": -11.894989,
-        "text": " request"
+        "text": " request",
+        "logprob": -11.894989
       }
     ],
-    "seed": null,
     "tokens": [
       {
         "id": 17,
+        "text": ".",
         "logprob": -1.8267672,
-        "text": "."
+        "special": false
       },
       {
         "id": 1587,
+        "text": "get",
         "logprob": -2.4674969,
-        "text": "get"
+        "special": false
       },
       {
         "id": 11,
+        "text": "(",
         "logprob": -1.906001,
-        "text": "("
+        "special": false
       },
       {
         "id": 5,
+        "text": "\"",
         "logprob": -1.2279545,
-        "text": "\""
+        "special": false
       },
       {
         "id": 4899,
+        "text": "action",
         "logprob": -4.170299,
-        "text": "action"
+        "special": false
       },
       {
         "id": 5,
+        "text": "\"",
         "logprob": -0.32478866,
-        "text": "\""
+        "special": false
       },
       {
         "id": 12,
+        "text": ")",
         "logprob": -1.0773665,
-        "text": ")"
+        "special": false
       },
       {
         "id": 30,
+        "text": ";",
         "logprob": -0.27640742,
-        "text": ";"
+        "special": false
       },
       {
         "id": 837,
+        "text": "\n       ",
         "logprob": -1.6970354,
-        "text": "\n       "
+        "special": false
       },
       {
         "id": 1320,
+        "text": " if",
         "logprob": -1.4495516,
-        "text": " if"
+        "special": false
       },
       {
         "id": 375,
+        "text": " (",
         "logprob": -0.23609057,
-        "text": " ("
+        "special": false
       },
       {
         "id": 4899,
+        "text": "action",
         "logprob": -1.1916996,
-        "text": "action"
+        "special": false
       },
       {
         "id": 3535,
+        "text": " ==",
         "logprob": -0.8918753,
-        "text": " =="
+        "special": false
       },
       {
         "id": 5109,
+        "text": " null",
         "logprob": -0.3933342,
-        "text": " null"
+        "special": false
       },
       {
         "id": 12,
+        "text": ")",
         "logprob": -0.43212673,
-        "text": ")"
+        "special": false
       },
       {
         "id": 731,
+        "text": " {",
         "logprob": -0.17702064,
-        "text": " {"
+        "special": false
       },
       {
         "id": 1260,
+        "text": "\n           ",
         "logprob": -0.07027565,
-        "text": "\n           "
+        "special": false
       },
       {
         "id": 10519,
+        "text": " throw",
         "logprob": -1.3915029,
-        "text": " throw"
+        "special": false
       },
       {
         "id": 2084,
+        "text": " new",
         "logprob": -0.04201372,
-        "text": " new"
+        "special": false
       },
       {
         "id": 150858,
+        "text": " RuntimeException",
         "logprob": -1.7329919,
-        "text": " RuntimeException"
+        "special": false
       }
     ]
-  },
-  "generated_text": ".get(\"action\");\n        if (action == null) {\n            throw new RuntimeException"
+  }
 }
\ No newline at end of file
diff --git a/launcher/tests/integration_tests.rs b/launcher/tests/integration_tests.rs
index b70b1628..0d2b6c74 100644
--- a/launcher/tests/integration_tests.rs
+++ b/launcher/tests/integration_tests.rs
@@ -14,6 +14,7 @@ pub struct Token {
     id: u32,
     text: String,
     logprob: Option<f32>,
+    special: bool,
 }
 
 #[derive(Deserialize)]
@@ -136,6 +137,7 @@ fn compare_results(result: GeneratedText, expected: GeneratedText) {
     {
         assert_eq!(token.id, expected_token.id);
         assert_eq!(token.text, expected_token.text);
+        assert_eq!(token.special, expected_token.special);
         if let Some(logprob) = token.logprob {
             let expected_logprob = expected_token.logprob.unwrap();
             assert_float_eq!(logprob, expected_logprob, abs <= 0.001);
diff --git a/launcher/tests/mt0_base.json b/launcher/tests/mt0_base.json
index cee3bc47..c06a2c26 100644
--- a/launcher/tests/mt0_base.json
+++ b/launcher/tests/mt0_base.json
@@ -1,117 +1,137 @@
 {
+  "generated_text": "\"\"\"Test the contents of the contents of the contents. \"\"\" test_test",
   "details": {
     "finish_reason": "length",
     "generated_tokens": 20,
+    "seed": null,
     "prefill": [
       {
         "id": 0,
-        "logprob": null,
-        "text": "<pad>"
+        "text": "<pad>",
+        "logprob": null
       }
     ],
-    "seed": null,
     "tokens": [
       {
         "id": 259,
+        "text": "",
         "logprob": -1.3656927,
-        "text": ""
+        "special": false
       },
       {
         "id": 215100,
+        "text": "\"\"\"",
         "logprob": -2.6551573,
-        "text": "\"\"\""
+        "special": false
       },
       {
         "id": 46138,
+        "text": "Test",
         "logprob": -1.8059857,
-        "text": "Test"
+        "special": false
       },
       {
         "id": 287,
+        "text": "the",
         "logprob": -1.2102449,
-        "text": "the"
+        "special": false
       },
       {
         "id": 259,
+        "text": "",
         "logprob": -1.6057279,
-        "text": ""
+        "special": false
       },
       {
         "id": 49076,
+        "text": "contents",
         "logprob": -3.6060903,
-        "text": "contents"
+        "special": false
       },
       {
         "id": 304,
+        "text": "of",
         "logprob": -0.5270343,
-        "text": "of"
+        "special": false
       },
       {
         "id": 287,
+        "text": "the",
         "logprob": -0.62522805,
-        "text": "the"
+        "special": false
       },
       {
         "id": 259,
+        "text": "",
         "logprob": -1.4069618,
-        "text": ""
+        "special": false
       },
       {
         "id": 49076,
+        "text": "contents",
         "logprob": -2.621994,
-        "text": "contents"
+        "special": false
       },
       {
         "id": 304,
+        "text": "of",
         "logprob": -1.3172221,
-        "text": "of"
+        "special": false
       },
       {
         "id": 287,
+        "text": "the",
         "logprob": -0.3501925,
-        "text": "the"
+        "special": false
       },
       {
         "id": 259,
+        "text": "",
         "logprob": -0.7219573,
-        "text": ""
+        "special": false
       },
       {
         "id": 49076,
+        "text": "contents",
         "logprob": -1.0494149,
-        "text": "contents"
+        "special": false
       },
       {
         "id": 260,
+        "text": ".",
         "logprob": -1.0803378,
-        "text": "."
+        "special": false
       },
       {
         "id": 259,
+        "text": "",
         "logprob": -0.32933083,
-        "text": ""
+        "special": false
       },
       {
         "id": 215100,
+        "text": "\"\"\"",
         "logprob": -0.11268901,
-        "text": "\"\"\""
+        "special": false
       },
       {
         "id": 2978,
+        "text": "test",
         "logprob": -1.5846587,
-        "text": "test"
+        "special": false
       },
       {
         "id": 290,
+        "text": "_",
         "logprob": -0.49796978,
-        "text": "_"
+        "special": false
       },
       {
         "id": 4125,
+        "text": "test",
         "logprob": -2.0026445,
-        "text": "test"
+        "special": false
       }
     ]
-  },
-  "generated_text": "\"\"\"Test the contents of the contents of the contents. \"\"\" test_test"
+  }
 }
\ No newline at end of file
diff --git a/proto/generate.proto b/proto/generate.proto
index 0c4f9626..28a61362 100644
--- a/proto/generate.proto
+++ b/proto/generate.proto
@@ -108,8 +108,10 @@ message Generation {
     float token_logprob = 4;
     /// Text
     string token_text = 5;
+    /// Is it a special token
+    bool token_is_special = 6;
     /// Complete generated text
-    GeneratedText generated_text = 6;
+    GeneratedText generated_text = 7;
 }
 
 message PrefillRequest {
diff --git a/router/src/infer.rs b/router/src/infer.rs
index dc0df50a..598c2fcf 100644
--- a/router/src/infer.rs
+++ b/router/src/infer.rs
@@ -1,7 +1,7 @@
 /// Batching and inference logic
 use crate::validation::{Validation, ValidationError};
-use crate::GenerateRequest;
 use crate::{Entry, Queue, Token};
+use crate::{GenerateRequest, PrefillToken};
 use nohash_hasher::IntMap;
 use std::sync::Arc;
 use text_generation_client::{
@@ -138,7 +138,7 @@ impl Infer {
                         .into_iter()
                         .zip(tokens.logprobs.into_iter())
                         .zip(tokens.texts.into_iter())
-                        .map(|((id, logprob), text)| Token { id, text, logprob })
+                        .map(|((id, logprob), text)| PrefillToken { id, text, logprob })
                         .collect();
                 }
                 // Push last token
@@ -372,6 +372,7 @@ fn send_generations(generations: Vec<Generation>, entries: &mut IntMap<u64, Entr
             id: generation.token_id,
             text: generation.token_text,
             logprob: generation.token_logprob,
+            special: generation.token_is_special,
         };
 
         if let Some(generated_text) = generation.generated_text {
@@ -420,7 +421,7 @@ pub(crate) enum InferStreamResponse {
 
 #[derive(Debug)]
 pub(crate) struct InferResponse {
-    pub(crate) prefill: Vec<Token>,
+    pub(crate) prefill: Vec<PrefillToken>,
     pub(crate) tokens: Vec<Token>,
     pub(crate) generated_text: GeneratedText,
     pub(crate) queued: Instant,
diff --git a/router/src/lib.rs b/router/src/lib.rs
index 8e3199dd..1f23bfd3 100644
--- a/router/src/lib.rs
+++ b/router/src/lib.rs
@@ -86,6 +86,16 @@ pub(crate) struct GenerateRequest {
     pub parameters: GenerateParameters,
 }
 
+#[derive(Debug, Serialize, ToSchema)]
+pub struct PrefillToken {
+    #[schema(example = 0)]
+    id: u32,
+    #[schema(example = "test")]
+    text: String,
+    #[schema(nullable = true, example = -0.34)]
+    logprob: f32,
+}
+
 #[derive(Debug, Serialize, ToSchema)]
 pub struct Token {
     #[schema(example = 0)]
@@ -94,6 +104,8 @@ pub struct Token {
     text: String,
     #[schema(nullable = true, example = -0.34)]
     logprob: f32,
+    #[schema(example = "false")]
+    special: bool,
 }
 
 #[derive(Serialize, ToSchema)]
@@ -116,7 +128,7 @@ pub(crate) struct Details {
     pub generated_tokens: u32,
     #[schema(example = 42)]
     pub seed: Option<u64>,
-    pub prefill: Option<Vec<Token>>,
+    pub prefill: Option<Vec<PrefillToken>>,
     pub tokens: Option<Vec<Token>>,
 }
 
diff --git a/router/src/server.rs b/router/src/server.rs
index 6acbbffa..de96e397 100644
--- a/router/src/server.rs
+++ b/router/src/server.rs
@@ -2,7 +2,7 @@
 use crate::infer::{InferError, InferStreamResponse};
 use crate::{
     Details, ErrorResponse, FinishReason, GenerateParameters, GenerateRequest, GenerateResponse,
-    Infer, StreamDetails, StreamResponse, Token, Validation,
+    Infer, PrefillToken, StreamDetails, StreamResponse, Token, Validation,
 };
 use axum::extract::Extension;
 use axum::http::{HeaderMap, Method, StatusCode};
@@ -255,11 +255,11 @@ async fn generate_stream(
                                     let time_per_token = inference_time / generated_text.generated_tokens;
 
                                     // Tracing metadata
-                                    span.record("total_time", format!("{:?}", total_time));
-                                    span.record("validation_time", format!("{:?}", validation_time));
-                                    span.record("queue_time", format!("{:?}", queue_time));
-                                    span.record("inference_time", format!("{:?}", inference_time));
-                                    span.record("time_per_token", format!("{:?}", time_per_token));
+                                    span.record("total_time", format!("{total_time:?}"));
+                                    span.record("validation_time", format!("{validation_time:?}"));
+                                    span.record("queue_time", format!("{queue_time:?}"));
+                                    span.record("inference_time", format!("{inference_time:?}"));
+                                    span.record("time_per_token", format!("{time_per_token:?}"));
                                     span.record("seed", format!("{:?}", generated_text.seed));
                                     tracing::info!(parent: &span, "Output: {}", generated_text.text);
 
@@ -349,6 +349,7 @@ pub async fn run(
             schemas(
                 GenerateRequest,
                 GenerateParameters,
+                PrefillToken,
                 Token,
                 GenerateResponse,
                 Details,
diff --git a/server/text_generation/models/causal_lm.py b/server/text_generation/models/causal_lm.py
index e109b83b..d15197d0 100644
--- a/server/text_generation/models/causal_lm.py
+++ b/server/text_generation/models/causal_lm.py
@@ -172,7 +172,9 @@ class CausalLMBatch(Batch):
             # and to remove unused allocated space
             left_offset = max_sequence_length - batch.max_sequence_length
             batch_left_offset = (
-                batch.attention_mask.shape[1] - batch.max_sequence_length - batch.padding_right_offset
+                batch.attention_mask.shape[1]
+                - batch.max_sequence_length
+                - batch.padding_right_offset
             )
             attention_mask[
                 start_index:end_index,
@@ -443,6 +445,7 @@ class CausalLM(Model):
                 next_token_id_squeezed,
                 next_token_logprob,
                 next_token_text,
+                next_token_id_squeezed in self.all_special_ids,
                 generated_text,
             )
 
diff --git a/server/text_generation/models/model.py b/server/text_generation/models/model.py
index ef6a5682..52480526 100644
--- a/server/text_generation/models/model.py
+++ b/server/text_generation/models/model.py
@@ -12,6 +12,7 @@ B = TypeVar("B", bound=Batch)
 class Model(ABC):
     def __init__(self, tokenizer: PreTrainedTokenizerBase, device: torch.device):
         self.tokenizer = tokenizer
+        self.all_special_ids = set(tokenizer.all_special_ids)
         self.device = device
 
     @property
diff --git a/server/text_generation/models/seq2seq_lm.py b/server/text_generation/models/seq2seq_lm.py
index 4813764b..3a4108ab 100644
--- a/server/text_generation/models/seq2seq_lm.py
+++ b/server/text_generation/models/seq2seq_lm.py
@@ -205,7 +205,8 @@ class Seq2SeqLMBatch(Batch):
             else:
                 batch_left_offset = (
                     batch.decoder_attention_mask.shape[1]
-                    - batch.max_decoder_input_length - batch.padding_right_offset
+                    - batch.max_decoder_input_length
+                    - batch.padding_right_offset
                 )
                 decoder_attention_mask[
                     start_index:end_index,
@@ -494,14 +495,10 @@ class Seq2SeqLM(Model):
 
             # Prefill
             if stopping_criteria.current_tokens == 1:
-                prefill_token_ids = decoder_input_ids[-new_decoder_input_length:-1]
-                prefill_texts = self.tokenizer.batch_decode(
-                    prefill_token_ids,
-                    clean_up_tokenization_spaces=False,
-                    skip_special_tokens=False,
-                )
                 prefill_tokens = PrefillTokens(
-                    prefill_token_ids, [float("nan")], prefill_texts
+                    [self.tokenizer.bos_token_id],
+                    [float("nan")],
+                    [self.tokenizer.bos_token],
                 )
             else:
                 prefill_tokens = None
@@ -512,6 +509,7 @@ class Seq2SeqLM(Model):
                 next_token_id_squeezed,
                 next_token_logprob,
                 next_token_text,
+                next_token_id_squeezed in self.all_special_ids,
                 generated_text,
             )
 
diff --git a/server/text_generation/models/types.py b/server/text_generation/models/types.py
index d1117b80..a3fbd6e8 100644
--- a/server/text_generation/models/types.py
+++ b/server/text_generation/models/types.py
@@ -73,6 +73,7 @@ class Generation:
     token_id: int
     token_logprob: float
     token_text: str
+    token_is_special: bool
     generated_text: Optional[GeneratedText]
 
     def to_pb(self) -> generate_pb2.Generation:
@@ -84,6 +85,7 @@ class Generation:
             token_id=self.token_id,
             token_logprob=self.token_logprob,
             token_text=self.token_text,
+            token_is_special=self.token_is_special,
             generated_text=self.generated_text.to_pb()
             if self.generated_text is not None
             else None,