diff --git a/Makefile b/Makefile
index 41527d387..809aa969f 100644
--- a/Makefile
+++ b/Makefile
@@ -40,9 +40,8 @@ black:
 flake8:
 	flake8 $(ALLPY)
 
-MYPY = pyteal scripts tests
 mypy:
-	mypy --show-error-codes $(MYPY)
+	mypy
 
 lint: black flake8 mypy
 
diff --git a/mypy.ini b/mypy.ini
index 728b3aef1..6545e4299 100644
--- a/mypy.ini
+++ b/mypy.ini
@@ -1,4 +1,6 @@
 [mypy]
+files = pyteal,scripts,tests
+python_version = 3.10
 
 [mypy-semantic_version.*]
 ignore_missing_imports = True
diff --git a/pyteal/ast/abi/array_base.py b/pyteal/ast/abi/array_base.py
index 8920637bc..7fdf51dc6 100644
--- a/pyteal/ast/abi/array_base.py
+++ b/pyteal/ast/abi/array_base.py
@@ -82,9 +82,9 @@ def decode(
         self,
         encoded: Expr,
         *,
-        start_index: Expr = None,
-        end_index: Expr = None,
-        length: Expr = None
+        start_index: Expr | None = None,
+        end_index: Expr | None = None,
+        length: Expr | None = None
     ) -> Expr:
         """Decode a substring of the passed in encoded byte string and set it as this type's value.
 
diff --git a/pyteal/ast/abi/bool.py b/pyteal/ast/abi/bool.py
index 6fa6d72a3..26f93bf1b 100644
--- a/pyteal/ast/abi/bool.py
+++ b/pyteal/ast/abi/bool.py
@@ -94,9 +94,9 @@ def decode(
         self,
         encoded: Expr,
         *,
-        start_index: Expr = None,
-        end_index: Expr = None,
-        length: Expr = None
+        start_index: Expr | None = None,
+        end_index: Expr | None = None,
+        length: Expr | None = None
     ) -> Expr:
         if start_index is None:
             start_index = Int(0)
diff --git a/pyteal/ast/abi/reference_type.py b/pyteal/ast/abi/reference_type.py
index e1a228245..7e9c5307c 100644
--- a/pyteal/ast/abi/reference_type.py
+++ b/pyteal/ast/abi/reference_type.py
@@ -64,9 +64,9 @@ def decode(
         self,
         encoded: Expr,
         *,
-        start_index: Expr = None,
-        end_index: Expr = None,
-        length: Expr = None,
+        start_index: Expr | None = None,
+        end_index: Expr | None = None,
+        length: Expr | None = None,
     ) -> Expr:
         return uint_decode(
             self.type_spec().bit_size(),
diff --git a/pyteal/ast/abi/transaction.py b/pyteal/ast/abi/transaction.py
index 69de7ea29..d10315514 100644
--- a/pyteal/ast/abi/transaction.py
+++ b/pyteal/ast/abi/transaction.py
@@ -63,7 +63,7 @@ def __str__(self) -> str:
 
 
 class Transaction(BaseType):
-    def __init__(self, spec: TransactionTypeSpec = None) -> None:
+    def __init__(self, spec: TransactionTypeSpec | None = None) -> None:
         if spec is None:
             super().__init__(TransactionTypeSpec())
         else:
@@ -97,9 +97,9 @@ def decode(
         self,
         encoded: Expr,
         *,
-        start_index: Expr = None,
-        end_index: Expr = None,
-        length: Expr = None,
+        start_index: Expr | None = None,
+        end_index: Expr | None = None,
+        length: Expr | None = None,
     ) -> Expr:
         raise TealInputError("A Transaction cannot be decoded")
 
diff --git a/pyteal/ast/abi/tuple.py b/pyteal/ast/abi/tuple.py
index 2d744eeeb..a4748d52c 100644
--- a/pyteal/ast/abi/tuple.py
+++ b/pyteal/ast/abi/tuple.py
@@ -302,9 +302,9 @@ def decode(
         self,
         encoded: Expr,
         *,
-        start_index: Expr = None,
-        end_index: Expr = None,
-        length: Expr = None,
+        start_index: Expr | None = None,
+        end_index: Expr | None = None,
+        length: Expr | None = None,
     ) -> Expr:
         extracted = substring_for_decoding(
             encoded, start_index=start_index, end_index=end_index, length=length
diff --git a/pyteal/ast/abi/type.py b/pyteal/ast/abi/type.py
index 6abed2d80..070ddc24a 100644
--- a/pyteal/ast/abi/type.py
+++ b/pyteal/ast/abi/type.py
@@ -98,9 +98,9 @@ def decode(
         self,
         encoded: Expr,
         *,
-        start_index: Expr = None,
-        end_index: Expr = None,
-        length: Expr = None,
+        start_index: Expr | None = None,
+        end_index: Expr | None = None,
+        length: Expr | None = None,
     ) -> Expr:
         """Decode a substring of the passed in encoded string and set it as this type's value.
 
diff --git a/pyteal/ast/abi/uint.py b/pyteal/ast/abi/uint.py
index 949eb7c40..0994adb03 100644
--- a/pyteal/ast/abi/uint.py
+++ b/pyteal/ast/abi/uint.py
@@ -281,9 +281,9 @@ def decode(
         self,
         encoded: Expr,
         *,
-        start_index: Expr = None,
-        end_index: Expr = None,
-        length: Expr = None,
+        start_index: Expr | None = None,
+        end_index: Expr | None = None,
+        length: Expr | None = None,
     ) -> Expr:
         return uint_decode(
             self.type_spec().bit_size(),
diff --git a/pyteal/ast/abi/util.py b/pyteal/ast/abi/util.py
index 4cece8b49..36b828390 100644
--- a/pyteal/ast/abi/util.py
+++ b/pyteal/ast/abi/util.py
@@ -22,9 +22,9 @@
 def substring_for_decoding(
     encoded: Expr,
     *,
-    start_index: Expr = None,
-    end_index: Expr = None,
-    length: Expr = None,
+    start_index: Expr | None = None,
+    end_index: Expr | None = None,
+    length: Expr | None = None,
 ) -> Expr:
     """A helper function for getting the substring to decode according to the rules of BaseType.decode."""
     if length is not None and end_index is not None:
diff --git a/pyteal/ast/acct_test.py b/pyteal/ast/acct_test.py
index 8259f8ac6..5991d2ac5 100644
--- a/pyteal/ast/acct_test.py
+++ b/pyteal/ast/acct_test.py
@@ -63,7 +63,7 @@ def test_acct_param_version_checks(method_name, field_name):
 
         account_param_field = AccountParamField[field_name]
 
-        def test_unsupported_version(version: int, match: str = None):
+        def test_unsupported_version(version: int, match: str | None = None):
             with pytest.raises(pt.TealInputError, match=match):
                 unsupported_options_version = pt.CompileOptions(version=version)
                 expr.__teal__(unsupported_options_version)
diff --git a/pyteal/ast/assert_.py b/pyteal/ast/assert_.py
index 22dd392dc..9444e9262 100644
--- a/pyteal/ast/assert_.py
+++ b/pyteal/ast/assert_.py
@@ -14,7 +14,7 @@ class Assert(Expr):
     """A control flow expression to verify that a condition is true."""
 
     def __init__(
-        self, cond: Expr, *additional_conds: Expr, comment: str = None
+        self, cond: Expr, *additional_conds: Expr, comment: str | None = None
     ) -> None:
         """Create an assert statement that raises an error if the condition is false.
 
diff --git a/pyteal/ast/bytes.py b/pyteal/ast/bytes.py
index 1c7bd09b4..1d842dfc3 100644
--- a/pyteal/ast/bytes.py
+++ b/pyteal/ast/bytes.py
@@ -21,7 +21,7 @@ def __init__(self, arg1: str | bytes | bytearray) -> None:
     def __init__(self, arg1: str, arg2: str) -> None:
         pass
 
-    def __init__(self, arg1: str | bytes | bytearray, arg2: str = None) -> None:
+    def __init__(self, arg1: str | bytes | bytearray, arg2: str | None = None) -> None:
         """
         __init__(arg1: Union[str, bytes, bytearray]) -> None
         __init__(self, arg1: str, arg2: str) -> None
diff --git a/pyteal/ast/comment.py b/pyteal/ast/comment.py
index 361694677..75263fe6f 100644
--- a/pyteal/ast/comment.py
+++ b/pyteal/ast/comment.py
@@ -43,7 +43,7 @@ def has_return(self):
 CommentExpr.__module__ = "pyteal"
 
 
-def Comment(comment: str, expr: Expr = None) -> Expr:
+def Comment(comment: str, expr: Expr | None = None) -> Expr:
     """Wrap an existing expression with a comment.
 
     This comment will be present in the compiled TEAL source immediately before the first op of the
diff --git a/pyteal/ast/if_.py b/pyteal/ast/if_.py
index 14cf9d394..18e0df3ad 100644
--- a/pyteal/ast/if_.py
+++ b/pyteal/ast/if_.py
@@ -17,7 +17,7 @@ class If(Expr):
     """Simple two-way conditional expression."""
 
     def __init__(
-        self, cond: Expr, thenBranch: Expr = None, elseBranch: Expr = None
+        self, cond: Expr, thenBranch: Expr | None = None, elseBranch: Expr | None = None
     ) -> None:
         """Create a new If expression.
 
diff --git a/pyteal/ast/maybe.py b/pyteal/ast/maybe.py
index 9ae1f0245..e22c79816 100644
--- a/pyteal/ast/maybe.py
+++ b/pyteal/ast/maybe.py
@@ -20,9 +20,9 @@ def __init__(
         op: Op,
         type: TealType,
         *,
-        immediate_args: List[Union[int, str]] = None,
-        args: List[Expr] = None,
-        compile_check: Callable[["CompileOptions"], None] = None,
+        immediate_args: List[Union[int, str]] | None = None,
+        args: List[Expr] | None = None,
+        compile_check: Callable[["CompileOptions"], None] | None = None,
     ):
         """Create a new MaybeValue.
 
diff --git a/pyteal/ast/multi.py b/pyteal/ast/multi.py
index e61af4b4a..4fed823a6 100644
--- a/pyteal/ast/multi.py
+++ b/pyteal/ast/multi.py
@@ -19,8 +19,8 @@ def __init__(
         op: Op,
         types: List[TealType],
         *,
-        immediate_args: List[Union[int, str]] = None,
-        args: List[Expr] = None,
+        immediate_args: List[Union[int, str]] | None = None,
+        args: List[Expr] | None = None,
         compile_check: Callable[["CompileOptions"], None] = lambda _: None,
     ):
         """Create a new MultiValue.
diff --git a/pyteal/ast/opup.py b/pyteal/ast/opup.py
index 419fe8e7f..6fe1cc05f 100644
--- a/pyteal/ast/opup.py
+++ b/pyteal/ast/opup.py
@@ -78,7 +78,7 @@ class OpUp:
             )
     """
 
-    def __init__(self, mode: OpUpMode, target_app_id: Expr = None):
+    def __init__(self, mode: OpUpMode, target_app_id: Expr | None = None):
         """Create a new OpUp object.
 
         Args:
diff --git a/pyteal/ast/return_.py b/pyteal/ast/return_.py
index d7537ec26..ba2b695a6 100644
--- a/pyteal/ast/return_.py
+++ b/pyteal/ast/return_.py
@@ -13,7 +13,7 @@
 class Return(Expr):
     """Return a value from the current execution context."""
 
-    def __init__(self, value: Expr = None) -> None:
+    def __init__(self, value: Expr | None = None) -> None:
         """Create a new Return expression.
 
         If called from the main program, this will immediately exit the program
diff --git a/pyteal/ast/router.py b/pyteal/ast/router.py
index 00e7d80a8..9041c8bbf 100644
--- a/pyteal/ast/router.py
+++ b/pyteal/ast/router.py
@@ -506,8 +506,8 @@ class Router:
     def __init__(
         self,
         name: str,
-        bare_calls: BareCallActions = None,
-        descr: str = None,
+        bare_calls: BareCallActions | None = None,
+        descr: str | None = None,
     ) -> None:
         """
         Args:
@@ -547,9 +547,9 @@ def __init__(
     def add_method_handler(
         self,
         method_call: ABIReturnSubroutine,
-        overriding_name: str = None,
-        method_config: MethodConfig = None,
-        description: str = None,
+        overriding_name: str | None = None,
+        method_config: MethodConfig | None = None,
+        description: str | None = None,
     ) -> ABIReturnSubroutine:
         """Add a method call handler to this Router.
 
@@ -605,17 +605,17 @@ def add_method_handler(
 
     def method(
         self,
-        func: Callable = None,
+        func: Callable | None = None,
         /,
         *,
-        name: str = None,
-        description: str = None,
-        no_op: CallConfig = None,
-        opt_in: CallConfig = None,
-        close_out: CallConfig = None,
-        clear_state: CallConfig = None,
-        update_application: CallConfig = None,
-        delete_application: CallConfig = None,
+        name: str | None = None,
+        description: str | None = None,
+        no_op: CallConfig | None = None,
+        opt_in: CallConfig | None = None,
+        close_out: CallConfig | None = None,
+        clear_state: CallConfig | None = None,
+        update_application: CallConfig | None = None,
+        delete_application: CallConfig | None = None,
     ):
         """This is an alternative way to register a method, as supposed to :code:`add_method_handler`.
 
diff --git a/pyteal/ast/router_test.py b/pyteal/ast/router_test.py
index b1e0f8401..609161860 100644
--- a/pyteal/ast/router_test.py
+++ b/pyteal/ast/router_test.py
@@ -259,7 +259,7 @@ def multiple_txn(
 ]
 
 
-def power_set(no_dup_list: list, length_override: int = None):
+def power_set(no_dup_list: list, length_override: int | None = None):
     """
     This function serves as a generator for all possible elements in power_set
     over `non_dup_list`, which is a list of non-duplicated elements (matches property of a set).
diff --git a/pyteal/ast/scratch.py b/pyteal/ast/scratch.py
index 463d83d5e..abf8821fe 100644
--- a/pyteal/ast/scratch.py
+++ b/pyteal/ast/scratch.py
@@ -1,4 +1,4 @@
-from typing import cast, TYPE_CHECKING, Optional
+from typing import cast, TYPE_CHECKING
 
 from pyteal.types import TealType, require_type
 from pyteal.config import NUM_SLOTS
@@ -17,7 +17,7 @@ class ScratchSlot:
     # Slot ids under 256 are manually reserved slots
     nextSlotId = NUM_SLOTS
 
-    def __init__(self, requestedSlotId: int = None):
+    def __init__(self, requestedSlotId: int | None = None):
         """Initializes a scratch slot with a particular id
 
         Args:
@@ -38,7 +38,7 @@ def __init__(self, requestedSlotId: int = None):
             self.id = requestedSlotId
             self.isReservedSlot = True
 
-    def store(self, value: Expr = None) -> Expr:
+    def store(self, value: Expr | None = None) -> Expr:
         """Get an expression to store a value in this slot.
 
         Args:
@@ -102,9 +102,9 @@ class ScratchLoad(Expr):
 
     def __init__(
         self,
-        slot: ScratchSlot = None,
+        slot: ScratchSlot | None = None,
         type: TealType = TealType.anytype,
-        index_expression: Expr = None,
+        index_expression: Expr | None = None,
     ):
         """Create a new ScratchLoad expression.
 
@@ -168,7 +168,10 @@ class ScratchStore(Expr):
     """Expression to store a value in scratch space."""
 
     def __init__(
-        self, slot: Optional[ScratchSlot], value: Expr, index_expression: Expr = None
+        self,
+        slot: ScratchSlot | None,
+        value: Expr,
+        index_expression: Expr | None = None,
     ):
         """Create a new ScratchStore expression.
 
diff --git a/pyteal/ast/scratchvar.py b/pyteal/ast/scratchvar.py
index a7d8a2dfa..f0a86e253 100644
--- a/pyteal/ast/scratchvar.py
+++ b/pyteal/ast/scratchvar.py
@@ -20,7 +20,7 @@ class ScratchVar(AbstractVar):
             ])
     """
 
-    def __init__(self, type: TealType = TealType.anytype, slotId: int = None):
+    def __init__(self, type: TealType = TealType.anytype, slotId: int | None = None):
         """Create a new ScratchVar with an optional type.
 
         Args:
diff --git a/pyteal/ast/subroutine.py b/pyteal/ast/subroutine.py
index eeea8950b..26ef53d90 100644
--- a/pyteal/ast/subroutine.py
+++ b/pyteal/ast/subroutine.py
@@ -133,7 +133,7 @@ def __init__(
         self.__name: str = name_str if name_str else self.implementation.__name__
 
     def _validate(
-        self, input_types: list[TealType | None] = None
+        self, input_types: list[TealType | None] | None = None
     ) -> tuple[
         MappingProxyType[str, Parameter],
         dict[str, type],
@@ -433,7 +433,7 @@ def __init__(
         subroutine: SubroutineDefinition,
         args: list[Expr | ScratchVar | abi.BaseType],
         *,
-        output_kwarg: OutputKwArgInfo = None,
+        output_kwarg: OutputKwArgInfo | None = None,
     ) -> None:
         super().__init__()
         self.subroutine = subroutine
@@ -674,7 +674,7 @@ def __call__(
     def name(self) -> str:
         return self.subroutine.name()
 
-    def method_signature(self, overriding_name: str = None) -> str:
+    def method_signature(self, overriding_name: str | None = None) -> str:
         if not self.is_abi_routable():
             raise TealInputError(
                 "Only registrable methods may return a method signature"
diff --git a/pyteal/ir/tealblock.py b/pyteal/ir/tealblock.py
index 7ce6259bc..8ceed472e 100644
--- a/pyteal/ir/tealblock.py
+++ b/pyteal/ir/tealblock.py
@@ -36,7 +36,9 @@ def isTerminal(self) -> bool:
         return len(self.getOutgoing()) == 0
 
     def validateTree(
-        self, parent: "TealBlock" = None, visited: List["TealBlock"] = None
+        self,
+        parent: "TealBlock | None" = None,
+        visited: List["TealBlock"] | None = None,
     ) -> None:
         """Check that this block and its children have valid parent pointers.
 
@@ -62,7 +64,9 @@ def validateTree(
                 block.validateTree(self, visited)
 
     def addIncoming(
-        self, parent: "TealBlock" = None, visited: List["TealBlock"] = None
+        self,
+        parent: "TealBlock | None" = None,
+        visited: List["TealBlock"] | None = None,
     ) -> None:
         """Calculate the parent blocks for this block and its children.
 
@@ -85,8 +89,8 @@ def addIncoming(
 
     def validateSlots(
         self,
-        slotsInUse: Set["ScratchSlot"] = None,
-        visited: Set[Tuple[int, ...]] = None,
+        slotsInUse: Set["ScratchSlot"] | None = None,
+        visited: Set[Tuple[int, ...]] | None = None,
     ) -> List[TealCompileError]:
         if visited is None:
             visited = set()
diff --git a/pyteal/ir/teallabel.py b/pyteal/ir/teallabel.py
index 6c6cea98e..5e515886d 100644
--- a/pyteal/ir/teallabel.py
+++ b/pyteal/ir/teallabel.py
@@ -1,4 +1,4 @@
-from typing import Optional, TYPE_CHECKING
+from typing import TYPE_CHECKING
 
 from pyteal.ir.tealcomponent import TealComponent
 from pyteal.ir.labelref import LabelReference
@@ -9,7 +9,7 @@
 
 class TealLabel(TealComponent):
     def __init__(
-        self, expr: Optional["Expr"], label: LabelReference, comment: str = None
+        self, expr: "Expr | None", label: LabelReference, comment: str | None = None
     ) -> None:
         super().__init__(expr)
         self.label = label
diff --git a/requirements.txt b/requirements.txt
index 158039a7b..5ff207492 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -2,7 +2,7 @@ black==22.3.0
 flake8==5.0.4
 flake8-tidy-imports==4.6.0
 graviton@git+https://github.com/algorand/graviton@v0.5.0
-mypy==0.950
+mypy==0.991
 pytest==7.2.0
 pytest-cov==3.0.0
 pytest-timeout==2.1.0