diff --git a/ops/matmul-inl.h b/ops/matmul-inl.h
index 8f91114..95277db 100644
--- a/ops/matmul-inl.h
+++ b/ops/matmul-inl.h
@@ -1179,7 +1179,7 @@ struct MMImpl {
 template <typename TA, typename TB, typename TC>
 HWY_NOINLINE MMPerKey* MatMul(const MatPtrT<TA>& A, const MatPtrT<TB>& B,
                               const float* HWY_RESTRICT add, MatMulEnv& env,
-                              MatPtrT<TC>& C) {
+                              MatPtrT<TC>& C, MMOptions options) {
   RowPtrs<TC> C_rows = GetOrSetTempRowPtrs(C, env.row_ptrs[0]);
 
   const Allocator& allocator = env.ctx.allocator;
@@ -1205,12 +1205,11 @@ HWY_NOINLINE MMPerKey* MatMul(const MatPtrT<TA>& A, const MatPtrT<TB>& B,
   MMPerKey& per_key = env.per_key[index];
   MMAutoTune<MMConfig>& tuner = per_key.autotune;
 
-  // Default to nested parallelism.
-  const ParallelismType parallelism_type = ParallelismType::kNested;
   const MMArgs args(env, per_key, static_cast<double>(A.Scale()) * B.Scale(),
                     add);
   if (HWY_LIKELY(tuner.Best())) {
-    MMImpl::DoMatMul(A, B, C_rows, args, *tuner.Best(), parallelism_type);
+    MMImpl::DoMatMul(A, B, C_rows, args, *tuner.Best(),
+                     options.parallelism_type);
     return &per_key;
   }
 
@@ -1239,7 +1238,7 @@ HWY_NOINLINE MMPerKey* MatMul(const MatPtrT<TA>& A, const MatPtrT<TB>& B,
 
   const MMConfig& cfg = tuner.NextConfig();
   const uint64_t t0 = hwy::timer::Start();
-  MMImpl::DoMatMul(A, B, C_rows, args, cfg, parallelism_type);
+  MMImpl::DoMatMul(A, B, C_rows, args, cfg, options.parallelism_type);
   const uint64_t t1 =
       env.have_timer_stop ? hwy::timer::Stop() : hwy::timer::Start();
   const double min_elapsed = static_cast<double>(tuner.NotifyTicks(t1 - t0)) /
diff --git a/ops/matmul.h b/ops/matmul.h
index dda9673..620d382 100644
--- a/ops/matmul.h
+++ b/ops/matmul.h
@@ -67,8 +67,8 @@ enum class ParallelismType : uint8_t {
 };
 
 struct MMOptions {
-  ParallelismType parallelism_type_ = ParallelismType::kNested;
-  uint8_t cluster_idx_ = 0;
+  ParallelismType parallelism_type = ParallelismType::kNested;
+  uint8_t cluster_idx = 0;
 };
 
 struct MMSequentialPolicy {
diff --git a/ops/matmul_static-inl.h b/ops/matmul_static-inl.h
index 28b21cf..ba09e0c 100644
--- a/ops/matmul_static-inl.h
+++ b/ops/matmul_static-inl.h
@@ -28,8 +28,8 @@
 #define GEMMA_MATMUL_DEFINE_ONE(TA, TB, TC)                             \
   MMPerKey* MatMulStatic(const MatPtrT<TA>& A, const MatPtrT<TB>& B,    \
                          const float* HWY_RESTRICT add, MatMulEnv& env, \
-                         MatPtrT<TC>& C) {                              \
-    return MatMul(A, B, add, env, C);                                   \
+                         MatPtrT<TC>& C, MMOptions options) {           \
+    return MatMul(A, B, add, env, C, options);                          \
   }
 
 #if defined(THIRD_PARTY_GEMMA_CPP_GEMMA_OPS_MATMUL_STATIC_INL_H_) == \
diff --git a/ops/matmul_static.h b/ops/matmul_static.h
index c06b87a..61dc505 100644
--- a/ops/matmul_static.h
+++ b/ops/matmul_static.h
@@ -35,7 +35,7 @@
 #define GEMMA_MATMUL_DECL_ONE(TA, TB, TC)                               \
   MMPerKey* MatMulStatic(const MatPtrT<TA>& A, const MatPtrT<TB>& B,    \
                          const float* HWY_RESTRICT add, MatMulEnv& env, \
-                         MatPtrT<TC>& C);
+                         MatPtrT<TC>& C, MMOptions options);
 
 // Passed to HWY_VISIT_TARGETS; declares all overloads for all targets.
 #define GEMMA_MATMUL_DECL(TARGET, NAMESPACE)                  \
diff --git a/ops/matmul_test.cc b/ops/matmul_test.cc
index 3a8528a..dc6f559 100644
--- a/ops/matmul_test.cc
+++ b/ops/matmul_test.cc
@@ -258,8 +258,9 @@ void TestMatMul(size_t rows_ac, size_t cols_a_rows_b, size_t cols_bc, bool add,
 
   MatMulSlow(A, BT, add_row, env, C_slow);
   // A few reps to get coverage of the various autotuned code paths.
+  MMOptions options;
   for (size_t rep = 0; rep < 16; ++rep) {
-    MMPerKey* per_key = MatMulStatic(A, BT, add_row, env, C);
+    MMPerKey* per_key = MatMulStatic(A, BT, add_row, env, C, options);
     AssertClose(A, BT, C_slow, C, env, line);
     if (per_key->autotune.Best()) break;
   }
diff --git a/ops/ops-inl.h b/ops/ops-inl.h
index caf8041..0438bf7 100644
--- a/ops/ops-inl.h
+++ b/ops/ops-inl.h
@@ -63,9 +63,10 @@ namespace hn = hwy::HWY_NAMESPACE;
 template <typename TA, typename TC>
 MMPerKey* CallMatMul(const MatPtrT<TA>& A, const MatPtr& B,
                      const float* HWY_RESTRICT add, MatMulEnv& env,
-                     MatPtrT<TC>& C) {
-  return CallUpcasted(
-      &B, [&](const auto* B_t) { return MatMulStatic(A, *B_t, add, env, C); });
+                     MatPtrT<TC>& C, const MMOptions& options = MMOptions()) {
+  return CallUpcasted(&B, [&](const auto* B_t) {
+    return MatMulStatic(A, *B_t, add, env, C, options);
+  });
 }
 
 HWY_INLINE double PackTokenAndProb(int32_t token, float prob) {