diff --git a/lib/OrdinaryDiffEqCore/Project.toml b/lib/OrdinaryDiffEqCore/Project.toml
index 870d14452b2..3e30d494135 100644
--- a/lib/OrdinaryDiffEqCore/Project.toml
+++ b/lib/OrdinaryDiffEqCore/Project.toml
@@ -1,7 +1,7 @@
 name = "OrdinaryDiffEqCore"
 uuid = "bbf590c4-e513-4bbe-9b18-05decba2e5d8"
 authors = ["ParamThakkar123 <paramthakkar864@gmail.com>"]
-version = "3.4.0"
+version = "3.4.1"
 
 [deps]
 SciMLOperators = "c0aeaf25-5076-4817-a8d5-81caf7dfa961"
@@ -37,6 +37,7 @@ DiffEqBase = "2b5f629d-d688-5b77-993f-72d75c75574e"
 FillArrays = "1a297f60-69ca-5386-bcde-b61e274b549b"
 Adapt = "79e6a3ab-5dfb-504d-930d-738a2a938a0e"
 Reexport = "189a3867-3050-52da-a836-e630ba90ab69"
+SparseArrays = "2f01184e-e22b-5df5-ae63-d93ebab69eaf"
 
 [extras]
 JET = "c3a54625-cd67-489e-a8e7-0a5a0ff4e31b"
@@ -98,12 +99,10 @@ Reexport = "1.2"
 [weakdeps]
 Mooncake = "da2b9cff-9c12-43a0-ae48-6db2b0edb7d6"
 EnzymeCore = "f151be2c-9106-41f4-ab19-57ee4f262869"
-SparseArrays = "2f01184e-e22b-5df5-ae63-d93ebab69eaf"
 
 [targets]
-test = ["DiffEqDevTools", "Random", "SafeTestsets", "SparseArrays", "Test", "Pkg"]
+test = ["DiffEqDevTools", "Random", "SafeTestsets", "Test", "Pkg"]
 
 [extensions]
 OrdinaryDiffEqCoreEnzymeCoreExt = "EnzymeCore"
 OrdinaryDiffEqCoreMooncakeExt = "Mooncake"
-OrdinaryDiffEqCoreSparseArraysExt = "SparseArrays"
diff --git a/lib/OrdinaryDiffEqCore/ext/OrdinaryDiffEqCoreSparseArraysExt.jl b/lib/OrdinaryDiffEqCore/ext/OrdinaryDiffEqCoreSparseArraysExt.jl
deleted file mode 100644
index 6b57562971f..00000000000
--- a/lib/OrdinaryDiffEqCore/ext/OrdinaryDiffEqCoreSparseArraysExt.jl
+++ /dev/null
@@ -1,25 +0,0 @@
-module OrdinaryDiffEqCoreSparseArraysExt
-
-using SparseArrays: SparseMatrixCSC
-import OrdinaryDiffEqCore: _isdiag
-
-# Efficient O(nnz) isdiag check for sparse matrices.
-# Standard isdiag is O(n²) which is prohibitively slow for large sparse matrices.
-"""
-    _isdiag(A::SparseMatrixCSC)
-
-Check if a sparse matrix is diagonal in O(nnz) time by traversing the CSC structure directly.
-Returns `true` if all non-zero elements are on the diagonal.
-"""
-function _isdiag(A::SparseMatrixCSC)
-    m, n = size(A)
-    m != n && return false
-    @inbounds for j in 1:n
-        for k in A.colptr[j]:(A.colptr[j + 1] - 1)
-            A.rowval[k] != j && return false
-        end
-    end
-    return true
-end
-
-end
diff --git a/lib/OrdinaryDiffEqCore/src/OrdinaryDiffEqCore.jl b/lib/OrdinaryDiffEqCore/src/OrdinaryDiffEqCore.jl
index e274231c5d0..989bfe9f06b 100644
--- a/lib/OrdinaryDiffEqCore/src/OrdinaryDiffEqCore.jl
+++ b/lib/OrdinaryDiffEqCore/src/OrdinaryDiffEqCore.jl
@@ -17,6 +17,8 @@ using MuladdMacro: @muladd
 
 using LinearAlgebra: opnorm, I, UniformScaling, diag, rank, isdiag
 
+import SparseArrays
+
 import PrecompileTools
 
 import FillArrays: Trues, Falses
diff --git a/lib/OrdinaryDiffEqCore/src/misc_utils.jl b/lib/OrdinaryDiffEqCore/src/misc_utils.jl
index 6698e14129c..5b0d576cf12 100644
--- a/lib/OrdinaryDiffEqCore/src/misc_utils.jl
+++ b/lib/OrdinaryDiffEqCore/src/misc_utils.jl
@@ -133,9 +133,27 @@ function get_differential_vars(f, u)
 end
 
 # Fallback for _isdiag - uses LinearAlgebra.isdiag which is O(n²)
-# Sparse specialization is provided in OrdinaryDiffEqCoreSparseArraysExt
 _isdiag(A::AbstractMatrix) = isdiag(A)
 
+# Efficient O(nnz) isdiag check for sparse matrices.
+# Standard isdiag is O(n²) which is prohibitively slow for large sparse matrices.
+"""
+    _isdiag(A::SparseMatrixCSC)
+
+Check if a sparse matrix is diagonal in O(nnz) time by traversing the CSC structure directly.
+Returns `true` if all non-zero elements are on the diagonal.
+"""
+function _isdiag(A::SparseArrays.SparseMatrixCSC)
+    m, n = size(A)
+    m != n && return false
+    @inbounds for j in 1:n
+        for k in A.colptr[j]:(A.colptr[j + 1] - 1)
+            A.rowval[k] != j && return false
+        end
+    end
+    return true
+end
+
 isnewton(::Any) = false
 
 function _bool_to_ADType(::Val{true}, ::Val{CS}, _) where {CS}
diff --git a/lib/OrdinaryDiffEqCore/test/sparse_isdiag_tests.jl b/lib/OrdinaryDiffEqCore/test/sparse_isdiag_tests.jl
index e8780dfd068..708234b9fd6 100644
--- a/lib/OrdinaryDiffEqCore/test/sparse_isdiag_tests.jl
+++ b/lib/OrdinaryDiffEqCore/test/sparse_isdiag_tests.jl
@@ -1,5 +1,4 @@
 using Test
-# Load SparseArrays first to trigger the extension
 using SparseArrays
 using OrdinaryDiffEqCore: _isdiag