diff --git a/letta/llm_api/openai_client.py b/letta/llm_api/openai_client.py
index 8eabfa27..3ef03792 100644
--- a/letta/llm_api/openai_client.py
+++ b/letta/llm_api/openai_client.py
@@ -639,6 +639,14 @@ class OpenAIClient(LLMClientBase):
                     tool.function.strict = False
         request_data = data.model_dump(exclude_unset=True)
 
+        # Fireworks uses strict validation (additionalProperties: false) and rejects
+        # reasoning fields that are not in their schema.
+        is_fireworks = llm_config.model_endpoint and "fireworks.ai" in llm_config.model_endpoint
+        if is_fireworks and "messages" in request_data:
+            for message in request_data["messages"]:
+                for field in ("reasoning_content_signature", "redacted_reasoning_content", "omitted_reasoning_content"):
+                    message.pop(field, None)
+
         # If Ollama
         # if llm_config.handle.startswith("ollama/") and llm_config.enable_reasoner:
         # Sadly, reasoning via the OpenAI proxy on Ollama only works for Harmony/gpt-oss