diff --git a/aana/core/models/chat.py b/aana/core/models/chat.py
index e6ea82e0..c102f3d6 100644
--- a/aana/core/models/chat.py
+++ b/aana/core/models/chat.py
@@ -132,6 +132,7 @@ class ChatCompletionRequest(BaseModel):
         temperature (float): float that controls the randomness of the sampling
         top_p (float): float that controls the cumulative probability of the top tokens to consider
         max_tokens (int): the maximum number of tokens to generate
+        repetition_penalty (float): float that penalizes new tokens based on whether they appear in the prompt and the generated text so far
         stream (bool): if set, partial message deltas will be sent
     """
 
@@ -139,8 +140,8 @@ class ChatCompletionRequest(BaseModel):
     messages: list[ChatMessage] = Field(
         ..., description="A list of messages comprising the conversation so far."
     )
-    temperature: float | None = Field(
-        default=None,
+    temperature: float = Field(
+        default=1.0,
         ge=0.0,
         description=(
             "Float that controls the randomness of the sampling. "
@@ -149,8 +150,8 @@ class ChatCompletionRequest(BaseModel):
             "Zero means greedy sampling."
         ),
     )
-    top_p: float | None = Field(
-        default=None,
+    top_p: float = Field(
+        default=1.0,
         gt=0.0,
         le=1.0,
         description=(
@@ -161,6 +162,15 @@ class ChatCompletionRequest(BaseModel):
     max_tokens: int | None = Field(
         default=None, ge=1, description="The maximum number of tokens to generate."
     )
+    repetition_penalty: float = Field(
+        default=1.0,
+        description=(
+            "Float that penalizes new tokens based on whether they appear in the "
+            "prompt and the generated text so far. Values > 1 encourage the model "
+            "to use new tokens, while values < 1 encourage the model to repeat tokens. "
+            "Default is 1.0 (no penalty)."
+        ),
+    )
 
     stream: bool | None = Field(
         default=False,