diff --git a/build.sh b/build.sh
index 492c033686..fee36c4084 100755
--- a/build.sh
+++ b/build.sh
@@ -125,12 +125,15 @@ fi
 OUTPUT_NAME=${OUTPUT_NAME:-$ENV}
 
 # Standalone environment build
+# -mavx2 enables AVX2 intrinsics (__m256, _mm256_*) which drive.h and
+# src/bf16.h use directly. x86_64 only — strip if porting to ARM/Apple Silicon.
+SIMD_FLAGS=(-mavx2 -mfma)
 if [ -n "$DEBUG" ] || [ "$MODE" = "local" ]; then
-    CLANG_OPT=(-g -O0 "${CLANG_WARN[@]}" "${SANITIZE_FLAGS[@]}")
+    CLANG_OPT=(-g -O0 "${CLANG_WARN[@]}" "${SANITIZE_FLAGS[@]}" "${SIMD_FLAGS[@]}")
     NVCC_OPT="-O0 -g"
     LINK_OPT="-g"
 else
-    CLANG_OPT=(-O2 -DNDEBUG "${CLANG_WARN[@]}")
+    CLANG_OPT=(-O2 -DNDEBUG "${CLANG_WARN[@]}" "${SIMD_FLAGS[@]}")
     NVCC_OPT="-O2 --threads 0"
     LINK_OPT="-O2"
 fi
diff --git a/src/bf16.h b/src/bf16.h
new file mode 100644
index 0000000000..8f95360d22
--- /dev/null
+++ b/src/bf16.h
@@ -0,0 +1,44 @@
+// Usage:
+//     #include "bf16.h"
+//
+//     Set env_name/binding.c obs to PrecisionTensor
+//
+//     bf16* observations;
+//     observations[0] = f32_to_bf16(some_float);                // scalar
+//
+//     // SIMD fast-path for inner loops with 8 floats already in an __m256:
+//     __m256 v = _mm256_mul_ps(x, scale);
+//     store_f32x8_as_bf16(&observations[i], v);                 // 1 store, 8 vals
+//
+//     // Reverse if you ever need to read back as float:
+//     float f = bf16_to_f32(observations[0]);
+//
+// x86_64 only — uses AVX intrinsics. To port to ARM/Apple Silicon, replace
+// store_f32x8_as_bf16 with a NEON equivalent (or remove and use scalar
+// f32_to_bf16 in a loop — the compiler auto-vectorizes well).
+
+#include <stdint.h>
+#include <string.h>
+#include <immintrin.h>
+
+typedef uint16_t bf16;
+
+static inline bf16 f32_to_bf16(float f) {
+    uint32_t bits;
+    memcpy(&bits, &f, 4);
+    return (uint16_t)(bits >> 16);
+}
+
+static inline float bf16_to_f32(bf16 b) {
+    uint32_t bits = (uint32_t)b << 16;
+    float f;
+    memcpy(&f, &bits, 4);
+    return f;
+}
+
+static inline void store_f32x8_as_bf16(bf16* dst, __m256 v) {
+    __m256i vi = _mm256_srli_epi32(_mm256_castps_si256(v), 16);
+    __m128i lo = _mm256_castsi256_si128(vi);
+    __m128i hi = _mm256_extracti128_si256(vi, 1);
+    _mm_storeu_si128((__m128i*)dst, _mm_packus_epi32(lo, hi));
+}
diff --git a/src/kernels.cu b/src/kernels.cu
index 0a6df9f45c..d9b25d8579 100644
--- a/src/kernels.cu
+++ b/src/kernels.cu
@@ -317,6 +317,13 @@ __global__ void cast(precision_t* __restrict__ dst,
     }
 }
 
+inline void cast_dispatch(precision_t* dst, const precision_t* src, int n, cudaStream_t stream) {
+    cudaMemcpyAsync(dst, src, n * sizeof(precision_t), cudaMemcpyDeviceToDevice, stream);
+}
+inline void cast_dispatch(precision_t* dst, const float* src, int n, cudaStream_t stream) {
+    cast<<<grid_size(n), BLOCK_SIZE, 0, stream>>>(dst, src, n);
+}
+
 #ifndef PRECISION_FLOAT
 __global__ void cast(float* __restrict__ dst,
         const precision_t* __restrict__ src, int n) {
diff --git a/src/pufferlib.cu b/src/pufferlib.cu
index 0014999e64..583d9a115f 100644
--- a/src/pufferlib.cu
+++ b/src/pufferlib.cu
@@ -600,8 +600,7 @@ extern "C" void net_callback_wrapper(void* ctx, int buf, int t) {
     OBS_TENSOR_T& obs_env = env.obs;
     int n = block_size * obs_env.shape[1];
     PrecisionTensor obs_dst = puf_slice(rollouts.observations, t, start, block_size);
-    cast<<<grid_size(n), BLOCK_SIZE, 0, stream>>>(
-        obs_dst.data, obs_env.data + (long)start*obs_env.shape[1], n);
+    cast_dispatch(obs_dst.data, obs_env.data + (long)start*obs_env.shape[1], n, stream);
 
     PrecisionTensor rew_dst = puf_slice(rollouts.rewards, t, start, block_size);
     n = block_size;
diff --git a/src/tensor.h b/src/tensor.h
index 8bf00d1c5f..7904bb9b70 100644
--- a/src/tensor.h
+++ b/src/tensor.h
@@ -30,6 +30,20 @@ typedef struct {
     precision_t* data;
     int64_t shape[PUF_MAX_DIMS];
 } PrecisionTensor;
+#else
+// C-compatible definition: precision_t is bf16 (uint16_t) or float depending on build mode.
+// Only the element size matters here (used by obs_element_size() in vecenv.h).
+#ifdef PRECISION_FLOAT
+typedef struct {
+    float* data;
+    int64_t shape[PUF_MAX_DIMS];
+} PrecisionTensor;
+#else
+typedef struct {
+    uint16_t* data;
+    int64_t shape[PUF_MAX_DIMS];
+} PrecisionTensor;
+#endif
 #endif
 
 #endif // PUFFERLIB_TENSOR_H