diff --git a/Project.toml b/Project.toml
index a14ded2..22582ab 100644
--- a/Project.toml
+++ b/Project.toml
@@ -52,7 +52,7 @@ ForwardDiff = "0.10.26"
 LinearAlgebra = "1.9, 1.10"
 MLDataDevices = "1"
 MLUtils = "0.4"
-ModelingToolkit = "9"
+ModelingToolkit = "9, 10"
 PDMats = "0.11"
 Reexport = "1.2"
 Requires = "1"
diff --git a/ext/OptimizationMTKExt.jl b/ext/OptimizationMTKExt.jl
index dbc08c4..a15ba31 100644
--- a/ext/OptimizationMTKExt.jl
+++ b/ext/OptimizationMTKExt.jl
@@ -20,7 +20,8 @@ function OptimizationBase.instantiate_function(
         ucons = fill(0.0,
             num_cons))))
     #sys = ModelingToolkit.structural_simplify(sys)
-    f = OptimizationProblem(sys, x, p, grad = g, hess = h,
+    # don't need to pass `x` or `p` since they're defaults now
+    f = OptimizationProblem(sys, nothing; grad = g, hess = h,
         sparse = true, cons_j = cons_j, cons_h = cons_h,
         cons_sparse = true).f
 
@@ -70,7 +71,8 @@ function OptimizationBase.instantiate_function(
         ucons = fill(0.0,
             num_cons))))
     #sys = ModelingToolkit.structural_simplify(sys)
-    f = OptimizationProblem(sys, cache.u0, cache.p, grad = g, hess = h,
+    # don't need to pass `x` or `p` since they're defaults now
+    f = OptimizationProblem(sys, nothing; grad = g, hess = h,
         sparse = true, cons_j = cons_j, cons_h = cons_h,
         cons_sparse = true).f
 
@@ -118,7 +120,8 @@ function OptimizationBase.instantiate_function(
         ucons = fill(0.0,
             num_cons))))
     #sys = ModelingToolkit.structural_simplify(sys)
-    f = OptimizationProblem(sys, x, p, grad = g, hess = h,
+    # don't need to pass `x` or `p` since they're defaults now
+    f = OptimizationProblem(sys, nothing; grad = g, hess = h,
         sparse = false, cons_j = cons_j, cons_h = cons_h,
         cons_sparse = false).f
 
@@ -168,7 +171,8 @@ function OptimizationBase.instantiate_function(
         ucons = fill(0.0,
             num_cons))))
     #sys = ModelingToolkit.structural_simplify(sys)
-    f = OptimizationProblem(sys, cache.u0, cache.p, grad = g, hess = h,
+    # don't need to pass `x` or `p` since they're defaults now
+    f = OptimizationProblem(sys, nothing; grad = g, hess = h,
         sparse = false, cons_j = cons_j, cons_h = cons_h,
         cons_sparse = false).f