diff --git a/service/models/operations/optimize.py b/service/models/operations/optimize.py
index 343b7b7..faf7bce 100644
--- a/service/models/operations/optimize.py
+++ b/service/models/operations/optimize.py
@@ -1,6 +1,6 @@
 from __future__ import annotations
 
-from typing import Any, ClassVar, Dict, List, Optional
+from typing import ClassVar, List, Optional
 from enum import Enum
 
 import numpy as np
@@ -77,7 +77,12 @@ class OptimizeExtra(BaseModel):
     maxfeval: int = 25
     alpha: float = 0.95
     solver_method: str = "dopri5"
-    solver_options: Dict[str, Any] = {}
+    # https://github.com/ciemss/pyciemss/blob/main/pyciemss/integration_utils/interface_checks.py
+    solver_step_size: float = Field(
+        None,
+        description="Step size required if solver method is euler.",
+        example=1.0,
+    )
 
 
 class Optimize(OperationRequest):
@@ -88,7 +93,7 @@ class Optimize(OperationRequest):
     fixed_static_parameter_interventions: list[HMIIntervention] = Field(
         None
     )  # Theses are interventions provided that will not be optimized
-    step_size: float = 1.0
+    logging_step_size: float = 1.0
     qoi: QOI
     risk_bound: float
     bounds_interventions: List[List[float]]
@@ -137,10 +142,17 @@ def gen_pyciemss_args(self, job_id):
             extra_options.pop("inferred_parameters"), job_id
         )
         n_samples_ouu = extra_options.pop("num_samples")
+        solver_options = {}
+        step_size = extra_options.pop(
+            "solver_step_size"
+        )  # Need to pop this out of extra.
+        solver_method = extra_options.pop("solver_method")
+        if step_size is not None and solver_method == "euler":
+            solver_options["step_size"] = step_size
 
         return {
             "model_path_or_json": amr_path,
-            "logging_step_size": self.step_size,
+            "logging_step_size": self.logging_step_size,
             "start_time": self.timespan.start,
             "end_time": self.timespan.end,
             "objfun": lambda x: objfun(
@@ -156,6 +168,8 @@ def gen_pyciemss_args(self, job_id):
             "fixed_static_parameter_interventions": fixed_static_parameter_interventions,
             "inferred_parameters": inferred_parameters,
             "n_samples_ouu": n_samples_ouu,
+            "solver_method": solver_method,
+            "solver_options": solver_options,
             **extra_options,
         }