diff --git a/.github/workflows/test.yml b/.github/workflows/test.yml
index 94747f38e8..4fa90bb270 100644
--- a/.github/workflows/test.yml
+++ b/.github/workflows/test.yml
@@ -183,7 +183,7 @@ jobs:
     - name: Run Clip tests for SD MLPerf on NULL backend
       run: DEV=NULL python -m pytest -n=auto test/external/mlperf_stable_diffusion/external_test_models.py::TestOpenClip --durations=20
     - name: Run AMD emulated BERT training on NULL backend
-      run: DEV=NULL::gfx1201 NULL_ALLOW_COPYOUT=1 CAPTURE_PROCESS_REPLAY=0 DEFAULT_FLOAT=HALF BENCHMARK=10 BS=66 GPUS=1 BERT_LAYERS=2 MODEL=bert python3 examples/mlperf/model_train.py
+      run: DEV=NULL::gfx1201 NULL_ALLOW_COPYOUT=1 DEFAULT_FLOAT=HALF BENCHMARK=10 BS=66 GPUS=1 BERT_LAYERS=2 MODEL=bert python3 examples/mlperf/model_train.py
     # TODO: support fake weights
     #- name: Run LLaMA 7B on 4 fake devices
     #  run: DEV=NULL python3 examples/llama.py --gen 1 --size 7B --shard 4 --prompt "Hello." --count 3 --temperature 0 --timing
@@ -348,9 +348,9 @@ jobs:
       - name: DEV=NULL beautiful_mnist_multigpu
         run: DEV=NULL NULL_ALLOW_COPYOUT=1 python examples/beautiful_mnist_multigpu.py
       - name: Test Bert training
-        run: DEV=NULL NULL_ALLOW_COPYOUT=1 CAPTURE_PROCESS_REPLAY=0 DEFAULT_FLOAT=HALF BENCHMARK=10 BS=24 GPUS=4 BERT_LAYERS=2 MODEL=bert python3 examples/mlperf/model_train.py
+        run: DEV=NULL NULL_ALLOW_COPYOUT=1 DEFAULT_FLOAT=HALF BENCHMARK=10 BS=24 GPUS=4 BERT_LAYERS=2 MODEL=bert python3 examples/mlperf/model_train.py
       - name: Test llama 3 training
-        run: DEV=NULL NULL_ALLOW_COPYOUT=1 CAPTURE_PROCESS_REPLAY=0 SAMPLES=300 BS=8 SEQLEN=512 GRADIENT_ACC_STEPS=1 FAKEDATA=1 DEFAULT_FLOAT=bfloat16 OPTIM_DTYPE=bfloat16 LLAMA3_SIZE=1B MODEL=llama3 python3 examples/mlperf/model_train.py
+        run: DEV=NULL NULL_ALLOW_COPYOUT=1 SAMPLES=300 BS=8 SEQLEN=512 GRADIENT_ACC_STEPS=1 FAKEDATA=1 DEFAULT_FLOAT=bfloat16 OPTIM_DTYPE=bfloat16 LLAMA3_SIZE=1B MODEL=llama3 python3 examples/mlperf/model_train.py
       - name: Run process replay tests
         uses: ./.github/actions/process-replay
 
diff --git a/examples/beautiful_cifar.py b/examples/beautiful_cifar.py
index ff66811e78..962523939c 100644
--- a/examples/beautiful_cifar.py
+++ b/examples/beautiful_cifar.py
@@ -9,8 +9,7 @@ from extra.lr_scheduler import OneCycleLR
 GPUS = [f'{Device.DEFAULT}:{i}' for i in range(getenv("GPUS", 1))]
 
 # override tinygrad defaults
-dtypes.default_float = dtypes.half
-Context(FUSE_OPTIM=1).__enter__()
+Context(DEFAULT_FLOAT=dtypes.half, FUSE_OPTIM=1).__enter__()
 
 # from https://github.com/tysam-code/hlb-CIFAR10/blob/main/main.py
 batchsize = getenv("BS", 1024)
diff --git a/test/backend/test_optim.py b/test/backend/test_optim.py
index 1d526dc596..299ec7a44d 100644
--- a/test/backend/test_optim.py
+++ b/test/backend/test_optim.py
@@ -143,12 +143,11 @@ class TestOptim(unittest.TestCase):
 
   @unittest.skipUnless(dtypes.half in Device[Device.DEFAULT].renderer.supported_dtypes(), "need half")
   def test_mixed_precision(self):
-    old_default_float, dtypes.default_float = dtypes.default_float, dtypes.half
+    self.enterContext(Context(DEFAULT_FLOAT=dtypes.half))
     # weight update would overflow without upcasting
     self._test_sgd(10, {'lr': 1e10}, 1e-6, 3e-4)
     self._test_adam(1, {'lr': 1e10}, 1e-4, 1e-4)
     self._test_adamw(1, {'lr': 1e10}, 1e-4, 1e-4)
-    dtypes.default_float = old_default_float
 
   def test_assert_tensor_train(self):
     t = Tensor.ones((1,1))
diff --git a/test/backend/test_randomness.py b/test/backend/test_randomness.py
index 97e4294360..ad5ee25842 100644
--- a/test/backend/test_randomness.py
+++ b/test/backend/test_randomness.py
@@ -232,17 +232,14 @@ class TestRandomness(unittest.TestCase):
   @given(strat.sampled_from([dtypes.float, dtypes.float16, dtypes.bfloat16]))
   def test_randn_finite(self, default_float):
     if default_float not in Device[Device.DEFAULT].renderer.supported_dtypes(): return
-    self.enterContext(Context(CAPTURE_PROCESS_REPLAY=0))  # TODO: make default dtype ContextVar
-    old_default_float = dtypes.default_float
     # low precision can result in inf from randn
-    dtypes.default_float = default_float
+    self.enterContext(Context(DEFAULT_FLOAT=default_float))
     t = Tensor.randn(64, 64)
     mx = t.max().numpy().item()
     mn = t.min().numpy().item()
     print(f"testing with {default_float=}")
     assert math.isfinite(mx), mx
     assert math.isfinite(mn), mn
-    dtypes.default_float = old_default_float
 
   def test_random_counter_overflow(self):
     device = Device.DEFAULT
diff --git a/test/external/external_benchmark_bert_matmuls.py b/test/external/external_benchmark_bert_matmuls.py
index fa2afd0388..fc630cf980 100644
--- a/test/external/external_benchmark_bert_matmuls.py
+++ b/test/external/external_benchmark_bert_matmuls.py
@@ -1,7 +1,8 @@
 from tinygrad import Tensor, dtypes
-dtypes.default_float = dtypes.float16
 from tinygrad.dtype import to_dtype
-from tinygrad.helpers import getenv
+from tinygrad.helpers import getenv, Context
+
+Context(DEFAULT_FLOAT=dtypes.float16).__enter__()
 
 if __name__ == "__main__":
   # matmuls in bert layers
diff --git a/test/external/external_benchmark_bert_softmax.py b/test/external/external_benchmark_bert_softmax.py
index 35b180fa94..5ed47d9492 100644
--- a/test/external/external_benchmark_bert_softmax.py
+++ b/test/external/external_benchmark_bert_softmax.py
@@ -1,9 +1,10 @@
 from tinygrad import Tensor, dtypes, GlobalCounters
-dtypes.default_float = dtypes.float16
 from tinygrad.dtype import to_dtype
-from tinygrad.helpers import getenv
+from tinygrad.helpers import getenv, Context
 from test.backend.test_softmax_fusion import single_kernel_softmax
 
+Context(DEFAULT_FLOAT=dtypes.float16).__enter__()
+
 if __name__ == "__main__":
   # softmax in bert layers
   BS = getenv("BS", 96//6)
diff --git a/test/external/external_test_jit_on_models.py b/test/external/external_test_jit_on_models.py
index e2d14d9768..6af6a706cc 100644
--- a/test/external/external_test_jit_on_models.py
+++ b/test/external/external_test_jit_on_models.py
@@ -3,6 +3,7 @@ import unittest
 import numpy as np
 from tinygrad import Tensor, dtypes
 from tinygrad.engine.jit import TinyJit
+from tinygrad.helpers import Context
 from test.helpers import derandomize_model
 
 from examples.llama import Transformer
@@ -14,8 +15,7 @@ def helper_test_jitted_correctness(gen, train, train_jit):
 
 class TestJittedModels(unittest.TestCase):
   def test_jitted_tiny_llama(self):
-    old_float = dtypes.default_float
-    dtypes.default_float = dtypes.float16
+    self.enterContext(Context(DEFAULT_FLOAT=dtypes.float16))
 
     args_tiny = {"dim": 1024, "hidden_dim": 1024, "n_heads": 8, "n_layers": 8, "norm_eps": 1e-05, "vocab_size": 1000}
     model = Transformer(**args_tiny)
@@ -25,7 +25,6 @@ class TestJittedModels(unittest.TestCase):
     @TinyJit
     def test_jit(t): return model(t, 0).realize()
     helper_test_jitted_correctness(lambda: (Tensor([[1,]]),), test, test_jit)
-    dtypes.default_float = old_float
 
   def test_jitted_stable_diffusion(self):
     from examples.stable_diffusion import UNetModel, unet_params
diff --git a/test/null/test_dtype_spec.py b/test/null/test_dtype_spec.py
index ac04ae5ca6..2aaebefe05 100644
--- a/test/null/test_dtype_spec.py
+++ b/test/null/test_dtype_spec.py
@@ -2,7 +2,7 @@ import unittest, math, struct, operator
 from tinygrad import Tensor, Device
 from tinygrad.dtype import DTYPES_DICT, dtypes, Invalid, truncate, float_to_fp16, float_to_bf16, _to_np_dtype, least_upper_dtype, least_upper_float
 
-from tinygrad.helpers import getenv
+from tinygrad.helpers import getenv, Context
 from hypothesis import given, settings, strategies as strat
 import numpy as np
 import torch
@@ -245,19 +245,14 @@ class TestTypePromotion(unittest.TestCase):
     assert least_upper_dtype(dtypes.weakfloat, dtypes.float64) == dtypes.float64
 
 class TestTypeSpec(unittest.TestCase):
-  def setUp(self):
-    self.old_default_int, self.old_default_float = dtypes.default_int, dtypes.default_float
-  def tearDown(self):
-    dtypes.default_int, dtypes.default_float = self.old_default_int, self.old_default_float
-
   def test_set_dtype_default(self):
     for default_int in [dtypes.int8, dtypes.int16, dtypes.int32, dtypes.int64]:
-      dtypes.default_int = default_int
-      assert dtypes.default_int == default_int
+      with Context(DEFAULT_INT=default_int):
+        assert dtypes.default_int == default_int
 
     for default_float in [*dtypes.fp8s, dtypes.float16, dtypes.bfloat16, dtypes.float32, dtypes.float64]:
-      dtypes.default_float = default_float
-      assert dtypes.default_float == default_float
+      with Context(DEFAULT_FLOAT=default_float):
+        assert dtypes.default_float == default_float
 
   @given(strat.sampled_from(core_dtypes), strat.sampled_from([operator.gt, operator.ge, operator.le, operator.lt, operator.eq, operator.ne]))
   def test_bool_ops(self, dtype, op):
@@ -265,7 +260,7 @@ class TestTypeSpec(unittest.TestCase):
 
   @given(strat.sampled_from(core_dtypes), strat.sampled_from(dtype_ints), strat.sampled_from(dtype_floats))
   def test_functions_return_index(self, dtype, default_int, default_float):
-    dtypes.default_int, dtypes.default_float = default_int, default_float
+    self.enterContext(Context(DEFAULT_INT=default_int, DEFAULT_FLOAT=default_float))
     assert Tensor([0, 1], dtype=dtype).argmax().dtype == dtypes.int32
     assert Tensor([0, 1], dtype=dtype).argmin().dtype == dtypes.int32
     assert Tensor([0, 1], dtype=dtype).multinomial().dtype == dtypes.int32
@@ -285,7 +280,7 @@ class TestTypeSpec(unittest.TestCase):
 
   @given(strat.sampled_from(dtype_floats), strat.sampled_from(dtype_floats))
   def test_attention_returns_same_dtype(self, data_dtype, default_float):
-    dtypes.default_float = default_float
+    self.enterContext(Context(DEFAULT_FLOAT=default_float))
     query = Tensor.rand(32, 8, 128, 64, dtype=data_dtype)
     key = Tensor.rand(32, 8, 128, 64, dtype=data_dtype)
     value = Tensor.rand(32, 8, 128, 64, dtype=data_dtype)
@@ -296,19 +291,14 @@ class TestTypeSpec(unittest.TestCase):
     assert query.scaled_dot_product_attention(key, value, attn_mask=mask).dtype == data_dtype
 
 class TestAutoCastType(unittest.TestCase):
-  def setUp(self):
-    self.old_default_int, self.old_default_float = dtypes.default_int, dtypes.default_float
-  def tearDown(self):
-    dtypes.default_int, dtypes.default_float = self.old_default_int, self.old_default_float
-
   @given(strat.sampled_from(dtype_floats), strat.sampled_from(dtype_floats))
   def test_least_upper_float_input_is_float(self, input_dtype, default_float):
-    dtypes.default_float = default_float
+    self.enterContext(Context(DEFAULT_FLOAT=default_float))
     self.assertEqual(least_upper_float(input_dtype), input_dtype)
 
   @given(strat.sampled_from(dtype_ints), strat.sampled_from(dtype_floats))
   def test_least_upper_float_input_is_int(self, input_dtype, default_float):
-    dtypes.default_float = default_float
+    self.enterContext(Context(DEFAULT_FLOAT=default_float))
     self.assertEqual(least_upper_float(input_dtype), default_float)
 
   @given(strat.sampled_from(core_dtypes))
@@ -332,7 +322,7 @@ class TestAutoCastType(unittest.TestCase):
 
   @given(strat.sampled_from(dtype_floats))
   def test_int_div_int(self, default_float):
-    dtypes.default_float = default_float
+    self.enterContext(Context(DEFAULT_FLOAT=default_float))
     self.assertEqual(Tensor([1]).div(Tensor([2])).dtype, default_float)
 
   def test_sum(self):
diff --git a/test/null/test_real_world.py b/test/null/test_real_world.py
index 0c058106ec..378e8b924b 100644
--- a/test/null/test_real_world.py
+++ b/test/null/test_real_world.py
@@ -47,13 +47,8 @@ class TestRealWorld(unittest.TestCase):
     gc.collect()
     global global_mem_used
     global_mem_used = GlobalCounters.mem_used
-    self.old_float = dtypes.default_float
-    self.enterContext(Context(CAPTURE_PROCESS_REPLAY=0))  # TODO: make default dtype ContextVar
     np.random.seed(2002)
 
-  def tearDown(self):
-    dtypes.default_float = self.old_float
-
   @slow
   @unittest.skipUnless(dtypes.float16 in supported_dtypes, "need dtypes.float16")
   def test_stable_diffusion(self):
@@ -82,7 +77,7 @@ class TestRealWorld(unittest.TestCase):
 
   @unittest.skipUnless(dtypes.float16 in supported_dtypes, "need dtypes.float16")
   def test_llama(self):
-    dtypes.default_float = dtypes.float16
+    self.enterContext(Context(DEFAULT_FLOAT=dtypes.float16))
 
     args_tiny = {"dim": 1024, "hidden_dim": 2048, "n_heads": 8, "n_layers": 8, "norm_eps": 1e-05, "vocab_size": 1000}
     model = LLaMaTransformer(**args_tiny)
@@ -94,7 +89,7 @@ class TestRealWorld(unittest.TestCase):
 
   @unittest.skipUnless(dtypes.float16 in supported_dtypes, "need dtypes.float16")
   def test_gpt2(self):
-    dtypes.default_float = dtypes.float16
+    self.enterContext(Context(DEFAULT_FLOAT=dtypes.float16))
 
     args_tiny = {"dim": 1024, "n_heads": 8, "n_layers": 8, "norm_eps": 1e-5, "vocab_size": 1000}
     model = GPT2Transformer(**args_tiny)
@@ -151,7 +146,7 @@ class TestRealWorld(unittest.TestCase):
 
   @unittest.skipUnless(dtypes.float16 in supported_dtypes, "need dtypes.float16")
   def test_train_cifar_hyp(self):
-    dtypes.default_float = dtypes.float16
+    self.enterContext(Context(DEFAULT_FLOAT=dtypes.float16))
     with Context(TRAINING=1):
       model = SpeedyResNet(Tensor.ones((12,3,2,2)))
       optimizer = optim.SGD(get_parameters(model), lr=0.01, momentum=hyp['opt']['momentum'], nesterov=True, weight_decay=hyp['opt']['bias_decay'])
diff --git a/test/null/test_schedule.py b/test/null/test_schedule.py
index 27f12864a5..7ca7d900ff 100644
--- a/test/null/test_schedule.py
+++ b/test/null/test_schedule.py
@@ -603,14 +603,12 @@ class TestSchedule(unittest.TestCase):
     check_schedule(p, 4)
 
   def test_conv2d(self, allowed=4, dtype=dtypes.float):
-    old_default_float, dtypes.default_float = dtypes.default_float, dtype
-    dtypes.default_float = dtype
+    self.enterContext(Context(DEFAULT_FLOAT=dtype))
     Tensor.manual_seed(0)
     BS, CIN = 2, 3
     img = Tensor.randn(BS, CIN, 64, 64).realize()
     w = Tensor.uniform(16, CIN, 3, 3).realize()
     ret = Tensor.conv2d(img, w).relu().mean().backward()
-    dtypes.default_float = old_default_float
     linear, var_vals = Tensor.linear_with_vars(ret, img.grad, w.grad)
     cnt = len([call for call in linear.src if call.src[0].op is Ops.SINK])
     assert cnt == allowed, f"expected {allowed} kernels, got {cnt}"
diff --git a/test/unit/test_dtype_spec.py b/test/unit/test_dtype_spec.py
index 2d60d2223c..cbb3bc5ba6 100644
--- a/test/unit/test_dtype_spec.py
+++ b/test/unit/test_dtype_spec.py
@@ -39,11 +39,13 @@ def _assert_eq(tensor:Tensor, target_dtype:DType, target, tol_target_dtype:float
     raise AssertionError(f"\ntensor {tensor.numpy()} dtype {tensor.dtype} does not match target {target} with dtype {target_dtype}") from e
 
 class TestTypeSpec(unittest.TestCase):
-  def setUp(self):
-    self.old_default_int, self.old_default_float = dtypes.default_int, dtypes.default_float
-    self.enterContext(Context(CAPTURE_PROCESS_REPLAY=0))  # TODO: make default dtype ContextVar
-  def tearDown(self):
-    dtypes.default_int, dtypes.default_float = self.old_default_int, self.old_default_float
+  def test_default_dtype_context(self):
+    default_float, default_int = dtypes.default_float, dtypes.default_int
+    with Context(DEFAULT_FLOAT=dtypes.half, DEFAULT_INT=dtypes.int16):
+      assert dtypes.default_float is dtypes.half
+      assert dtypes.default_int is dtypes.int16
+    assert dtypes.default_float is default_float
+    assert dtypes.default_int is default_int
 
   @unittest.skip("this test is slow and spawning whole pythons")
   def test_env_set_default_float(self):
@@ -82,7 +84,7 @@ class TestTypeSpec(unittest.TestCase):
 
   @given(strat.sampled_from(dtype_ints), strat.sampled_from(dtype_floats))
   def test_creation(self, default_int, default_float):
-    dtypes.default_int, dtypes.default_float = default_int, default_float
+    self.enterContext(Context(DEFAULT_INT=default_int, DEFAULT_FLOAT=default_float))
     _assert_eq(Tensor(True), dtypes.bool, True)
     _assert_eq(Tensor(None), dtypes.weakfloat, [])
     _assert_eq(Tensor(2), dtypes.weakint, 2)
@@ -101,7 +103,7 @@ class TestTypeSpec(unittest.TestCase):
 
   @given(strat.sampled_from(dtype_ints), strat.sampled_from(dtype_floats))
   def test_full(self, default_int, default_float):
-    dtypes.default_int, dtypes.default_float = default_int, default_float
+    self.enterContext(Context(DEFAULT_INT=default_int, DEFAULT_FLOAT=default_float))
 
     _assert_eq(Tensor.zeros((2, 3)), dtypes.default_float, np.zeros((2, 3)))
     _assert_eq(Tensor.zeros((2, 3), dtype=dtypes.int64), dtypes.int64, np.zeros((2, 3)))
@@ -124,7 +126,7 @@ class TestTypeSpec(unittest.TestCase):
 
   @given(strat.sampled_from(dtype_ints), strat.sampled_from(dtype_floats))
   def test_reduce_0d_default(self, default_int, default_float):
-    dtypes.default_int, dtypes.default_float = default_int, default_float
+    self.enterContext(Context(DEFAULT_INT=default_int, DEFAULT_FLOAT=default_float))
     _assert_eq(Tensor.ones((2,3,0)).sum(2), dtypes.default_float, np.zeros((2, 3)))
     # TODO: what should this one be?
     # _assert_eq(Tensor.ones((2,3,0), dtype=dtypes.default_int).sum(2), dtypes.default_int, np.zeros((2, 3)))
@@ -132,7 +134,7 @@ class TestTypeSpec(unittest.TestCase):
 
   @given(strat.sampled_from(dtype_ints), strat.sampled_from(dtype_floats))
   def test_arange(self, default_int, default_float):
-    dtypes.default_int, dtypes.default_float = default_int, default_float
+    self.enterContext(Context(DEFAULT_INT=default_int, DEFAULT_FLOAT=default_float))
 
     _assert_eq(Tensor.arange(5), dtypes.default_int, np.arange(5))
     _assert_eq(Tensor.arange(120), dtypes.default_int, np.arange(120))
@@ -149,12 +151,6 @@ class TestTypeSpec(unittest.TestCase):
     _assert_eq(Tensor.arange(5.0, 3.0), dtypes.default_float, np.arange(5.0, 3.0))
 
 class TestAutoCastType(unittest.TestCase):
-  def setUp(self):
-    self.old_default_int, self.old_default_float = dtypes.default_int, dtypes.default_float
-    self.enterContext(Context(CAPTURE_PROCESS_REPLAY=0))  # TODO: make default dtype ContextVar
-  def tearDown(self):
-    dtypes.default_int, dtypes.default_float = self.old_default_int, self.old_default_float
-
   def test_int_sqrt(self):
     _assert_eq(Tensor([1, 4, 9, 16]).sqrt(), dtypes.default_float, [1, 2, 3, 4])
 
@@ -194,22 +190,18 @@ class TestAutoCastType(unittest.TestCase):
     np.testing.assert_allclose(t.prod(dtype=dtypes.float32).numpy(), 20000)
 
   def test_gradient_dtype(self):
-    old_default_float = dtypes.default_float
-
     for default_dtype in dtypes.floats:
       if default_dtype not in supported_dtypes: continue
-      dtypes.default_float = default_dtype
-      for dtype in dtypes.floats:
-        if dtype not in supported_dtypes: continue
-        if DEBUG >= 2:
-          print(f"testing {default_dtype=}, {dtype=}")
-        a = Tensor([1, 2, 3], dtype=dtype)
-        b = (a * 5).sum()
-        b.backward()  # if there is dtype mismatch, lazy should assert
-        assert a.grad.dtype == a.dtype
-        np.testing.assert_allclose(a.grad.numpy(), [5, 5, 5])
-
-    dtypes.default_float = old_default_float
+      with Context(DEFAULT_FLOAT=default_dtype):
+        for dtype in dtypes.floats:
+          if dtype not in supported_dtypes: continue
+          if DEBUG >= 2:
+            print(f"testing {default_dtype=}, {dtype=}")
+          a = Tensor([1, 2, 3], dtype=dtype)
+          b = (a * 5).sum()
+          b.backward()  # if there is dtype mismatch, lazy should assert
+          assert a.grad.dtype == a.dtype
+          np.testing.assert_allclose(a.grad.numpy(), [5, 5, 5])
 
   @unittest.skipIf(Device.DEFAULT == "PYTHON", "very slow")
   @slow
diff --git a/tinygrad/codegen/__init__.py b/tinygrad/codegen/__init__.py
index f690245bba..17693ed9d4 100644
--- a/tinygrad/codegen/__init__.py
+++ b/tinygrad/codegen/__init__.py
@@ -1,7 +1,7 @@
 from dataclasses import replace, dataclass
 import itertools, functools
 from tinygrad.helpers import DISABLE_FAST_IDIV, TRANSCENDENTAL, SPEC, DEBUG, VIZ, IMAGE, NOOPT, EMULATED_DTYPES, NOLOCALS, USE_TC
-from tinygrad.helpers import ALLOW_TF32, TracingKey, Context, panic
+from tinygrad.helpers import ALLOW_TF32, DEFAULT_FLOAT, DEFAULT_INT, TracingKey, Context, panic
 from tinygrad.uop.ops import PatternMatcher, graph_rewrite, UOp, pm_lower_index_dtype, Ops, UPat, track_rewrites, KernelInfo, ProgramInfo, GroupOp
 from tinygrad.uop.ops import AxisType
 from tinygrad.uop.render import pyrender
@@ -450,7 +450,7 @@ def do_to_program(ast:UOp, renderer:Renderer) -> UOp:
 
 to_program_cache: dict[tuple, UOp] = {}
 def to_program(ast:UOp, renderer:Renderer) -> UOp:
-  config = (NOOPT, EMULATED_DTYPES, NOLOCALS, USE_TC, IMAGE, DISABLE_FAST_IDIV, TRANSCENDENTAL, ALLOW_TF32)
+  config = (NOOPT, EMULATED_DTYPES, NOLOCALS, USE_TC, IMAGE, DISABLE_FAST_IDIV, TRANSCENDENTAL, ALLOW_TF32, DEFAULT_FLOAT, DEFAULT_INT)
   key = (ast.key, type(renderer), renderer.target, *[x.value for x in config])
   if (prg:=to_program_cache.get(key)) is None: to_program_cache[key] = prg = do_to_program(ast, renderer)
   return prg
diff --git a/tinygrad/dtype.py b/tinygrad/dtype.py
index eddc38a4f2..2e97e9a8de 100644
--- a/tinygrad/dtype.py
+++ b/tinygrad/dtype.py
@@ -2,7 +2,7 @@ from __future__ import annotations
 from typing import Final, ClassVar, Callable, Literal
 import math, struct, ctypes, functools
 from dataclasses import dataclass, fields
-from tinygrad.helpers import getenv
+from tinygrad.helpers import getenv, DEFAULT_FLOAT, DEFAULT_INT
 from enum import IntEnum, auto
 
 class ConstFloat(float):
@@ -83,7 +83,7 @@ class DType(metaclass=DTypeMetaClass):
     return ConstFloat(float(val)) if dtypes.is_float(self) else bool(val) if dtypes.is_bool(self) else int(val)
 
 
-class dtypes:
+class DTypes:
   @staticmethod
   @functools.cache
   def is_float(x: DType) -> bool: return x in (dtypes.floats + (dtypes.weakfloat,))
@@ -138,8 +138,10 @@ class dtypes:
   uchar = uint8; ushort = uint16; uint = uint32; ulong = uint64 # noqa: E702
   char = int8; short = int16; int = int32; long = int64 # noqa: E702
 
-  default_float: ClassVar[DType] = float32
-  default_int: ClassVar[DType] = int32
+  @property
+  def default_float(self) -> DType: return to_dtype(DEFAULT_FLOAT.value)
+  @property
+  def default_int(self) -> DType: return to_dtype(DEFAULT_INT.value)
 
   fp8_ocp = (fp8e4m3, fp8e5m2)
   fp8_fnuz = (fp8e4m3fnuz, fp8e5m2fnuz)
@@ -155,12 +157,12 @@ class dtypes:
   weaks = (weakint, weakfloat)
   all = floats + ints + (bool,) # noqa: A003
 
-if (env_default_float := getenv("DEFAULT_FLOAT", "")):
-  dtypes.default_float = getattr(dtypes, env_default_float.lower())
-  assert dtypes.is_float(dtypes.default_float), f"{env_default_float} is not a float dtype"
+dtypes = DTypes()
 
 DTypeLike = str|DType
 def to_dtype(dtype:DTypeLike) -> DType: return dtype if isinstance(dtype, DType) else getattr(dtypes, dtype.lower())
+assert dtypes.is_float(dtypes.default_float), f"{DEFAULT_FLOAT.value} is not a float dtype"
+assert dtypes.is_int(dtypes.default_int), f"{DEFAULT_INT.value} is not an int dtype"
 def strong_dtype(dtype:DType) -> DType:
   return {dtypes.weakint: dtypes.default_int, dtypes.weakfloat: dtypes.default_float}.get(dtype, dtype)
 
@@ -184,7 +186,7 @@ def least_upper_dtype(*ds:DType) -> DType:
 def least_upper_float(dt:DType) -> DType:
   return dtypes.weakfloat if dt is dtypes.weakint else dt if dtypes.is_float(dt) else least_upper_dtype(dt, dtypes.default_float)
 
-DTYPES_DICT = {k: v for k, v in dtypes.__dict__.items() if isinstance(v, DType) and not k.startswith(("default", "void", "weak", "_"))}
+DTYPES_DICT = {k: v for k, v in DTypes.__dict__.items() if isinstance(v, DType) and not k.startswith(("default", "void", "weak", "_"))}
 INVERSE_DTYPES_DICT = {**{v.name:k for k,v in DTYPES_DICT.items()}, "void": "void", "weakint":"weakint", "weakfloat":"weakfloat"}
 
 @functools.cache
diff --git a/tinygrad/helpers.py b/tinygrad/helpers.py
index 5b7e9891a8..86d0136b18 100644
--- a/tinygrad/helpers.py
+++ b/tinygrad/helpers.py
@@ -247,6 +247,7 @@ FUSE_OPTIM = ContextVar("FUSE_OPTIM", 0)
 ALLOW_DEVICE_USAGE, MAX_BUFFER_SIZE = ContextVar("ALLOW_DEVICE_USAGE", 1), ContextVar("MAX_BUFFER_SIZE", 0)
 MAX_KERNEL_BUFFERS = ContextVar("MAX_KERNEL_BUFFERS", 0)
 EMULATED_DTYPES = ContextVar("EMULATED_DTYPES", "")
+DEFAULT_FLOAT, DEFAULT_INT = ContextVar("DEFAULT_FLOAT", "float32"), ContextVar("DEFAULT_INT", "int32")
 CAPTURE_PROCESS_REPLAY = ContextVar("CAPTURE_PROCESS_REPLAY", 0)
 def _get_cpu_count() -> int:
   # os.process_cpu_count (3.13+) respects cgroup limits