diff --git a/eval_protocol/pytest/remote_rollout_processor.py b/eval_protocol/pytest/remote_rollout_processor.py
index a5a00d1d..5031f6fe 100644
--- a/eval_protocol/pytest/remote_rollout_processor.py
+++ b/eval_protocol/pytest/remote_rollout_processor.py
@@ -1,4 +1,5 @@
 import asyncio
+import base64
 import time
 from typing import Any, Dict, List, Optional, Callable
 
@@ -25,7 +26,9 @@
 logger = logging.getLogger(__name__)
 
 
-def _build_fireworks_tracing_url(base_url: str, metadata: RolloutMetadata) -> str:
+def _build_fireworks_tracing_url(
+    base_url: str, metadata: RolloutMetadata, completion_params_base_url: Optional[str] = None
+) -> str:
     """Build a Fireworks tracing URL by appending rollout metadata to the base URL path,
     allowing the Fireworks tracing proxy to automatically tag traces.
 
@@ -35,8 +38,9 @@ def _build_fireworks_tracing_url(base_url: str, metadata: RolloutMetadata) -> st
         base_url: Fireworks tracing proxy URL (we expect this to be https://tracing.fireworks.ai or
                   https://tracing.fireworks.ai/project_id/{project_id})
         metadata: Rollout metadata containing IDs to embed in the URL
+        completion_params_base_url: Optional LLM base URL to encode and append to the final URL
     """
-    return (
+    url = (
         f"{base_url}/rollout_id/{metadata.rollout_id}"
         f"/invocation_id/{metadata.invocation_id}"
         f"/experiment_id/{metadata.experiment_id}"
@@ -44,6 +48,14 @@ def _build_fireworks_tracing_url(base_url: str, metadata: RolloutMetadata) -> st
         f"/row_id/{metadata.row_id}"
     )
 
+    if (
+        completion_params_base_url
+    ):  # The final URL is both tracing.fireworks.ai and the actual LLM base URL we want to use
+        encoded_base_url = base64.urlsafe_b64encode(completion_params_base_url.encode()).decode()
+        url = f"{url}/encoded_base_url/{encoded_base_url}"
+
+    return url
+
 
 def _default_output_data_loader(config: DataLoaderConfig) -> DynamicDataLoader:
     """Default output data loader that fetches traces from Fireworks tracing proxy.
@@ -164,6 +176,13 @@ async def _process_row(row: EvaluationRow) -> EvaluationRow:
                     "Model must be provided in row.input_metadata.completion_params or config.completion_params"
                 )
 
+            # Extract base_url from completion_params if provided. If we're using tracing.fireworks.ai, this base_url gets encoded and passed to LiteLLM inside the proxy.
+            completion_params_base_url: Optional[str] = None
+            if row.input_metadata and row.input_metadata.completion_params:
+                completion_params_base_url = row.input_metadata.completion_params.get("base_url")
+            if completion_params_base_url is None and config.completion_params:
+                completion_params_base_url = config.completion_params.get("base_url")
+
             # Strip non-OpenAI fields from messages before sending to remote
             allowed_message_fields = {"role", "content", "tool_calls", "tool_call_id", "name"}
             clean_messages = []
@@ -192,7 +211,7 @@ async def _process_row(row: EvaluationRow) -> EvaluationRow:
                 model_base_url.startswith("https://tracing.fireworks.ai")
                 or model_base_url.startswith("http://localhost")
             ):
-                final_model_base_url = _build_fireworks_tracing_url(model_base_url, meta)
+                final_model_base_url = _build_fireworks_tracing_url(model_base_url, meta, completion_params_base_url)
 
             init_payload: InitRequest = InitRequest(
                 model=model,