diff --git a/libc/cmake/modules/LLVMLibCObjectRules.cmake b/libc/cmake/modules/LLVMLibCObjectRules.cmake
--- a/libc/cmake/modules/LLVMLibCObjectRules.cmake
+++ b/libc/cmake/modules/LLVMLibCObjectRules.cmake
@@ -108,7 +108,7 @@
     target_compile_options(${gpu_target_name} PRIVATE ${compile_options})
     target_include_directories(${gpu_target_name} PRIVATE ${include_dirs})
     add_dependencies(${gpu_target_name} ${ADD_GPU_ENTRYPOINT_OBJ_DEPENDS})
-    target_compile_definitions(${gpu_target_name} PRIVATE LLVM_LIBC_PUBLIC_PACKAGING)
+    target_compile_definitions(${gpu_target_name} PRIVATE LIBC_COPT_PUBLIC_PACKAGING)
 
     # Append this target to a list of images to package into a single binary.
     set(input_file $<TARGET_OBJECTS:${gpu_target_name}>)
@@ -521,7 +521,7 @@
       ${ADD_ENTRYPOINT_OBJ_SRCS}
       ${ADD_ENTRYPOINT_OBJ_HDRS}
     )
-    target_compile_options(${fq_target_name} BEFORE PRIVATE ${common_compile_options} -DLLVM_LIBC_PUBLIC_PACKAGING)
+    target_compile_options(${fq_target_name} BEFORE PRIVATE ${common_compile_options} -DLIBC_COPT_PUBLIC_PACKAGING)
     target_include_directories(${fq_target_name} PRIVATE ${include_dirs})
     add_dependencies(${fq_target_name} ${full_deps_list})
 
diff --git a/libc/common_libc_tuners.cmake b/libc/common_libc_tuners.cmake
--- a/libc/common_libc_tuners.cmake
+++ b/libc/common_libc_tuners.cmake
@@ -9,6 +9,6 @@
   if(LLVM_USE_SANITIZER)
     message(FATAL_ERROR "LIBC_UNSAFE_STRING_WIDE_READ is set at the same time as a sanitizer. LIBC_UNSAFE_STRING_WIDE_READ causes strlen and memchr to read beyond the end of their target strings, which is undefined behavior caught by sanitizers.")
   else()
-    list(APPEND LIBC_COMMON_TUNE_OPTIONS "-DLIBC_UNSAFE_STRING_WIDE_READ")
+    list(APPEND LIBC_COMMON_TUNE_OPTIONS "-DLIBC_COPT_UNSAFE_STRING_WIDE_READ")
     endif()
 endif()
diff --git a/libc/fuzzing/stdlib/CMakeLists.txt b/libc/fuzzing/stdlib/CMakeLists.txt
--- a/libc/fuzzing/stdlib/CMakeLists.txt
+++ b/libc/fuzzing/stdlib/CMakeLists.txt
@@ -58,7 +58,7 @@
     libc.src.stdlib.strtoul
     libc.src.stdlib.strtoull
   COMPILE_OPTIONS
-    -DLLVM_LIBC_FUZZ_ATOI_CLEANER_INPUT
+    -DLIBC_COPT_FUZZ_ATOI_CLEANER_INPUT
 )
 
 add_libc_fuzzer(
diff --git a/libc/fuzzing/stdlib/strtointeger_differential_fuzz.cpp b/libc/fuzzing/stdlib/strtointeger_differential_fuzz.cpp
--- a/libc/fuzzing/stdlib/strtointeger_differential_fuzz.cpp
+++ b/libc/fuzzing/stdlib/strtointeger_differential_fuzz.cpp
@@ -50,7 +50,7 @@
   size_t i;
 
   for (i = 0; i < size; ++i) {
-#ifdef LLVM_LIBC_FUZZ_ATOI_CLEANER_INPUT
+#ifdef LIBC_COPT_FUZZ_ATOI_CLEANER_INPUT
     container[i] = VALID_CHARS[data[i] % sizeof(VALID_CHARS)];
 #else
     container[i] = data[i];
diff --git a/libc/src/__support/common.h b/libc/src/__support/common.h
--- a/libc/src/__support/common.h
+++ b/libc/src/__support/common.h
@@ -17,13 +17,13 @@
 #endif
 
 // GPU targets do not support aliasing.
-#if defined(LLVM_LIBC_PUBLIC_PACKAGING) && defined(LIBC_TARGET_ARCH_IS_GPU)
+#if defined(LIBC_COPT_PUBLIC_PACKAGING) && defined(LIBC_TARGET_ARCH_IS_GPU)
 #define LLVM_LIBC_FUNCTION(type, name, arglist)                                \
   LLVM_LIBC_FUNCTION_ATTR decltype(__llvm_libc::name)                          \
       __##name##_impl__ __asm__(#name);                                        \
   type __##name##_impl__ arglist
 // MacOS needs to be excluded because it does not support aliasing.
-#elif defined(LLVM_LIBC_PUBLIC_PACKAGING) && (!defined(__APPLE__))
+#elif defined(LIBC_COPT_PUBLIC_PACKAGING) && (!defined(__APPLE__))
 #define LLVM_LIBC_FUNCTION(type, name, arglist)                                \
   LLVM_LIBC_FUNCTION_ATTR decltype(__llvm_libc::name)                          \
       __##name##_impl__ __asm__(#name);                                        \
diff --git a/libc/src/__support/str_to_float.h b/libc/src/__support/str_to_float.h
--- a/libc/src/__support/str_to_float.h
+++ b/libc/src/__support/str_to_float.h
@@ -616,15 +616,15 @@
     return;
   }
 
-#ifndef LLVM_LIBC_DISABLE_CLINGER_FAST_PATH
+#ifndef LIBC_COPT_STRTOFLOAT_DISABLE_CLINGER_FAST_PATH
   if (!truncated) {
     if (clinger_fast_path<T>(mantissa, exp10, outputMantissa, outputExp2)) {
       return;
     }
   }
-#endif // LLVM_LIBC_DISABLE_CLINGER_FAST_PATH
+#endif // LIBC_COPT_STRTOFLOAT_DISABLE_CLINGER_FAST_PATH
 
-#ifndef LLVM_LIBC_DISABLE_EISEL_LEMIRE
+#ifndef LIBC_COPT_STRTOFLOAT_DISABLE_EISEL_LEMIRE
   // Try Eisel-Lemire
   if (eisel_lemire<T>(mantissa, exp10, outputMantissa, outputExp2)) {
     if (!truncated) {
@@ -641,11 +641,13 @@
       }
     }
   }
-#endif // LLVM_LIBC_DISABLE_EISEL_LEMIRE
+#endif // LIBC_COPT_STRTOFLOAT_DISABLE_EISEL_LEMIRE
 
-#ifndef LLVM_LIBC_DISABLE_SIMPLE_DECIMAL_CONVERSION
+#ifndef LIBC_COPT_STRTOFLOAT_DISABLE_SIMPLE_DECIMAL_CONVERSION
   simple_decimal_conversion<T>(numStart, outputMantissa, outputExp2);
-#endif // LLVM_LIBC_DISABLE_SIMPLE_DECIMAL_CONVERSION
+#else
+#warning "Simple decimal conversion is disabled, result may not be correct."
+#endif // LIBC_COPT_STRTOFLOAT_DISABLE_SIMPLE_DECIMAL_CONVERSION
 
   return;
 }
diff --git a/libc/src/stdio/printf_core/converter.cpp b/libc/src/stdio/printf_core/converter.cpp
--- a/libc/src/stdio/printf_core/converter.cpp
+++ b/libc/src/stdio/printf_core/converter.cpp
@@ -13,10 +13,10 @@
 
 // This option allows for replacing all of the conversion functions with custom
 // replacements. This allows conversions to be replaced at compile time.
-#ifndef LLVM_LIBC_PRINTF_CONV_ATLAS
+#ifndef LIBC_COPT_PRINTF_CONV_ATLAS
 #include "src/stdio/printf_core/converter_atlas.h"
 #else
-#include LLVM_LIBC_PRINTF_CONV_ATLAS
+#include LIBC_COPT_PRINTF_CONV_ATLAS
 #endif
 
 #include <stddef.h>
@@ -42,7 +42,7 @@
   case 'x':
   case 'X':
     return convert_int(writer, to_conv);
-#ifndef LLVM_LIBC_PRINTF_DISABLE_FLOAT
+#ifndef LIBC_COPT_PRINTF_DISABLE_FLOAT
   case 'f':
   case 'F':
     return convert_float_decimal(writer, to_conv);
@@ -55,11 +55,11 @@
   case 'g':
   case 'G':
     return convert_float_dec_auto(writer, to_conv);
-#endif // LLVM_LIBC_PRINTF_DISABLE_FLOAT
-#ifndef LLVM_LIBC_PRINTF_DISABLE_WRITE_INT
+#endif // LIBC_COPT_PRINTF_DISABLE_FLOAT
+#ifndef LIBC_COPT_PRINTF_DISABLE_WRITE_INT
   case 'n':
     return convert_write_int(writer, to_conv);
-#endif // LLVM_LIBC_PRINTF_DISABLE_WRITE_INT
+#endif // LIBC_COPT_PRINTF_DISABLE_WRITE_INT
   case 'p':
     return convert_pointer(writer, to_conv);
   default:
diff --git a/libc/src/stdio/printf_core/converter_atlas.h b/libc/src/stdio/printf_core/converter_atlas.h
--- a/libc/src/stdio/printf_core/converter_atlas.h
+++ b/libc/src/stdio/printf_core/converter_atlas.h
@@ -22,18 +22,18 @@
 // defines convert_int
 #include "src/stdio/printf_core/int_converter.h"
 
-#ifndef LLVM_LIBC_PRINTF_DISABLE_FLOAT
+#ifndef LIBC_COPT_PRINTF_DISABLE_FLOAT
 // defines convert_float_decimal
 // defines convert_float_dec_exp
 // defines convert_float_dec_auto
 #include "src/stdio/printf_core/float_dec_converter.h"
 // defines convert_float_hex_exp
 #include "src/stdio/printf_core/float_hex_converter.h"
-#endif // LLVM_LIBC_PRINTF_DISABLE_FLOAT
+#endif // LIBC_COPT_PRINTF_DISABLE_FLOAT
 
-#ifndef LLVM_LIBC_PRINTF_DISABLE_WRITE_INT
+#ifndef LIBC_COPT_PRINTF_DISABLE_WRITE_INT
 #include "src/stdio/printf_core/write_int_converter.h"
-#endif // LLVM_LIBC_PRINTF_DISABLE_WRITE_INT
+#endif // LIBC_COPT_PRINTF_DISABLE_WRITE_INT
 
 // defines convert_pointer
 #include "src/stdio/printf_core/ptr_converter.h"
diff --git a/libc/src/stdio/printf_core/parser.h b/libc/src/stdio/printf_core/parser.h
--- a/libc/src/stdio/printf_core/parser.h
+++ b/libc/src/stdio/printf_core/parser.h
@@ -26,7 +26,7 @@
   size_t cur_pos = 0;
   internal::ArgList args_cur;
 
-#ifndef LLVM_LIBC_PRINTF_DISABLE_INDEX_MODE
+#ifndef LIBC_COPT_PRINTF_DISABLE_INDEX_MODE
   // args_start stores the start of the va_args, which is allows getting the
   // value of arguments that have already been passed. args_index is tracked so
   // that we know which argument args_cur is on.
@@ -34,7 +34,7 @@
   size_t args_index = 1;
 
   // Defined in printf_config.h
-  static constexpr size_t DESC_ARR_LEN = LLVM_LIBC_PRINTF_INDEX_ARR_LEN;
+  static constexpr size_t DESC_ARR_LEN = LIBC_COPT_PRINTF_INDEX_ARR_LEN;
 
   // desc_arr stores the sizes of the variables in the ArgList. This is used in
   // index mode to reduce repeated string parsing. The sizes are stored as
@@ -45,16 +45,16 @@
 
   // TODO: Look into object stores for optimization.
 
-#endif // LLVM_LIBC_PRINTF_DISABLE_INDEX_MODE
+#endif // LIBC_COPT_PRINTF_DISABLE_INDEX_MODE
 
 public:
-#ifndef LLVM_LIBC_PRINTF_DISABLE_INDEX_MODE
+#ifndef LIBC_COPT_PRINTF_DISABLE_INDEX_MODE
   LIBC_INLINE Parser(const char *__restrict new_str, internal::ArgList &args)
       : str(new_str), args_cur(args), args_start(args) {}
 #else
   LIBC_INLINE Parser(const char *__restrict new_str, internal::ArgList &args)
       : str(new_str), args_cur(args) {}
-#endif // LLVM_LIBC_PRINTF_DISABLE_INDEX_MODE
+#endif // LIBC_COPT_PRINTF_DISABLE_INDEX_MODE
 
   // get_next_section will parse the format string until it has a fully
   // specified format section. This can either be a raw format section with no
@@ -84,7 +84,7 @@
   // INDEX MODE ONLY FUNCTIONS AFTER HERE:
   //----------------------------------------------------
 
-#ifndef LLVM_LIBC_PRINTF_DISABLE_INDEX_MODE
+#ifndef LIBC_COPT_PRINTF_DISABLE_INDEX_MODE
 
   // parse_index parses the index of a value inside a format string. It
   // assumes that str[*local_pos] points to character after a '%' or '*', and
@@ -124,7 +124,7 @@
   // modify cur_pos.
   TypeDesc get_type_desc(size_t index);
 
-#endif // LLVM_LIBC_PRINTF_DISABLE_INDEX_MODE
+#endif // LIBC_COPT_PRINTF_DISABLE_INDEX_MODE
 };
 
 } // namespace printf_core
diff --git a/libc/src/stdio/printf_core/parser.cpp b/libc/src/stdio/printf_core/parser.cpp
--- a/libc/src/stdio/printf_core/parser.cpp
+++ b/libc/src/stdio/printf_core/parser.cpp
@@ -6,7 +6,7 @@
 //
 //===----------------------------------------------------------------------===//
 
-// #define LLVM_LIBC_PRINTF_DISABLE_INDEX_MODE 1 // This will be a compile flag.
+// #define LIBC_COPT_PRINTF_DISABLE_INDEX_MODE 1 // This will be a compile flag.
 
 #include "parser.h"
 
@@ -22,11 +22,11 @@
 namespace __llvm_libc {
 namespace printf_core {
 
-#ifndef LLVM_LIBC_PRINTF_DISABLE_INDEX_MODE
+#ifndef LIBC_COPT_PRINTF_DISABLE_INDEX_MODE
 #define GET_ARG_VAL_SIMPLEST(arg_type, index) get_arg_value<arg_type>(index)
 #else
 #define GET_ARG_VAL_SIMPLEST(arg_type, _) get_next_arg_value<arg_type>()
-#endif // LLVM_LIBC_PRINTF_DISABLE_INDEX_MODE
+#endif // LIBC_COPT_PRINTF_DISABLE_INDEX_MODE
 
 FormatSection Parser::get_next_section() {
   FormatSection section;
@@ -38,9 +38,9 @@
     ++cur_pos;
     [[maybe_unused]] size_t conv_index = 0;
 
-#ifndef LLVM_LIBC_PRINTF_DISABLE_INDEX_MODE
+#ifndef LIBC_COPT_PRINTF_DISABLE_INDEX_MODE
     conv_index = parse_index(&cur_pos);
-#endif // LLVM_LIBC_PRINTF_DISABLE_INDEX_MODE
+#endif // LIBC_COPT_PRINTF_DISABLE_INDEX_MODE
 
     section.flags = parse_flags(&cur_pos);
 
@@ -120,7 +120,7 @@
         break;
       }
       break;
-#ifndef LLVM_LIBC_PRINTF_DISABLE_FLOAT
+#ifndef LIBC_COPT_PRINTF_DISABLE_FLOAT
     case ('f'):
     case ('F'):
     case ('e'):
@@ -137,10 +137,10 @@
             cpp::bit_cast<fputil::FPBits<long double>::UIntType>(
                 GET_ARG_VAL_SIMPLEST(long double, conv_index));
       break;
-#endif // LLVM_LIBC_PRINTF_DISABLE_FLOAT
-#ifndef LLVM_LIBC_PRINTF_DISABLE_WRITE_INT
+#endif // LIBC_COPT_PRINTF_DISABLE_FLOAT
+#ifndef LIBC_COPT_PRINTF_DISABLE_WRITE_INT
     case ('n'):
-#endif // LLVM_LIBC_PRINTF_DISABLE_WRITE_INT
+#endif // LIBC_COPT_PRINTF_DISABLE_WRITE_INT
     case ('p'):
     case ('s'):
       section.conv_val_ptr = GET_ARG_VAL_SIMPLEST(void *, conv_index);
@@ -233,7 +233,7 @@
 // INDEX MODE ONLY FUNCTIONS AFTER HERE:
 //----------------------------------------------------
 
-#ifndef LLVM_LIBC_PRINTF_DISABLE_INDEX_MODE
+#ifndef LIBC_COPT_PRINTF_DISABLE_INDEX_MODE
 
 size_t Parser::parse_index(size_t *local_pos) {
   if (internal::isdigit(str[*local_pos])) {
@@ -343,7 +343,7 @@
           break;
         }
         break;
-#ifndef LLVM_LIBC_PRINTF_DISABLE_FLOAT
+#ifndef LIBC_COPT_PRINTF_DISABLE_FLOAT
       case ('f'):
       case ('F'):
       case ('e'):
@@ -357,10 +357,10 @@
         else
           conv_size = type_desc_from_type<long double>();
         break;
-#endif // LLVM_LIBC_PRINTF_DISABLE_FLOAT
-#ifndef LLVM_LIBC_PRINTF_DISABLE_WRITE_INT
+#endif // LIBC_COPT_PRINTF_DISABLE_FLOAT
+#ifndef LIBC_COPT_PRINTF_DISABLE_WRITE_INT
       case ('n'):
-#endif // LLVM_LIBC_PRINTF_DISABLE_WRITE_INT
+#endif // LIBC_COPT_PRINTF_DISABLE_WRITE_INT
       case ('p'):
       case ('s'):
         conv_size = type_desc_from_type<void *>();
@@ -403,13 +403,13 @@
       args_cur.next_var<uint32_t>();
     else if (cur_type_desc == type_desc_from_type<uint64_t>())
       args_cur.next_var<uint64_t>();
-#ifndef LLVM_LIBC_PRINTF_DISABLE_FLOAT
+#ifndef LIBC_COPT_PRINTF_DISABLE_FLOAT
     // Floating point numbers are stored separately from the other arguments.
     else if (cur_type_desc == type_desc_from_type<double>())
       args_cur.next_var<double>();
     else if (cur_type_desc == type_desc_from_type<long double>())
       args_cur.next_var<long double>();
-#endif // LLVM_LIBC_PRINTF_DISABLE_FLOAT
+#endif // LIBC_COPT_PRINTF_DISABLE_FLOAT
     // pointers may be stored separately from normal values.
     else if (cur_type_desc == type_desc_from_type<void *>())
       args_cur.next_var<void *>();
@@ -420,7 +420,7 @@
   }
 }
 
-#endif // LLVM_LIBC_PRINTF_DISABLE_INDEX_MODE
+#endif // LIBC_COPT_PRINTF_DISABLE_INDEX_MODE
 
 } // namespace printf_core
 } // namespace __llvm_libc
diff --git a/libc/src/stdio/printf_core/printf_config.h b/libc/src/stdio/printf_core/printf_config.h
--- a/libc/src/stdio/printf_core/printf_config.h
+++ b/libc/src/stdio/printf_core/printf_config.h
@@ -25,8 +25,8 @@
 // the index array is 10, then when the 20th index is requested the first 10
 // types can be found immediately, and then the format string must be parsed 10
 // times to find the types of the next 10 arguments.
-#ifndef LLVM_LIBC_PRINTF_INDEX_ARR_LEN
-#define LLVM_LIBC_PRINTF_INDEX_ARR_LEN 128
+#ifndef LIBC_COPT_PRINTF_INDEX_ARR_LEN
+#define LIBC_COPT_PRINTF_INDEX_ARR_LEN 128
 #endif
 
 // TODO(michaelrj): Move the other printf configuration options into this file.
diff --git a/libc/src/stdio/scanf_core/converter.cpp b/libc/src/stdio/scanf_core/converter.cpp
--- a/libc/src/stdio/scanf_core/converter.cpp
+++ b/libc/src/stdio/scanf_core/converter.cpp
@@ -12,9 +12,9 @@
 #include "src/stdio/scanf_core/core_structs.h"
 #include "src/stdio/scanf_core/reader.h"
 
-#ifndef LLVM_LIBC_SCANF_DISABLE_FLOAT
+#ifndef LIBC_COPT_SCANF_DISABLE_FLOAT
 #include "src/stdio/scanf_core/float_converter.h"
-#endif // LLVM_LIBC_SCANF_DISABLE_FLOAT
+#endif // LIBC_COPT_SCANF_DISABLE_FLOAT
 #include "src/stdio/scanf_core/current_pos_converter.h"
 #include "src/stdio/scanf_core/int_converter.h"
 #include "src/stdio/scanf_core/ptr_converter.h"
@@ -48,7 +48,7 @@
     if (ret_val != READ_OK)
       return ret_val;
     return convert_int(reader, to_conv);
-#ifndef LLVM_LIBC_SCANF_DISABLE_FLOAT
+#ifndef LIBC_COPT_SCANF_DISABLE_FLOAT
   case 'f':
   case 'F':
   case 'e':
@@ -61,7 +61,7 @@
     if (ret_val != READ_OK)
       return ret_val;
     return convert_float(reader, to_conv);
-#endif // LLVM_LIBC_SCANF_DISABLE_FLOAT
+#endif // LIBC_COPT_SCANF_DISABLE_FLOAT
   case 'n':
     return convert_current_pos(reader, to_conv);
   case 'p':
diff --git a/libc/src/stdio/scanf_core/parser.h b/libc/src/stdio/scanf_core/parser.h
--- a/libc/src/stdio/scanf_core/parser.h
+++ b/libc/src/stdio/scanf_core/parser.h
@@ -25,22 +25,22 @@
   size_t cur_pos = 0;
   internal::ArgList args_cur;
 
-#ifndef LLVM_LIBC_SCANF_DISABLE_INDEX_MODE
+#ifndef LIBC_COPT_SCANF_DISABLE_INDEX_MODE
   // args_start stores the start of the va_args, which is used when a previous
   // argument is needed. In that case, we have to read the arguments from the
   // beginning since they don't support reading backwards.
   internal::ArgList args_start;
   size_t args_index = 1;
-#endif // LLVM_LIBC_SCANF_DISABLE_INDEX_MODE
+#endif // LIBC_COPT_SCANF_DISABLE_INDEX_MODE
 
 public:
-#ifndef LLVM_LIBC_SCANF_DISABLE_INDEX_MODE
+#ifndef LIBC_COPT_SCANF_DISABLE_INDEX_MODE
   LIBC_INLINE Parser(const char *__restrict new_str, internal::ArgList &args)
       : str(new_str), args_cur(args), args_start(args) {}
 #else
   LIBC_INLINE Parser(const char *__restrict new_str, internal::ArgList &args)
       : str(new_str), args_cur(args) {}
-#endif // LLVM_LIBC_SCANF_DISABLE_INDEX_MODE
+#endif // LIBC_COPT_SCANF_DISABLE_INDEX_MODE
 
   // get_next_section will parse the format string until it has a fully
   // specified format section. This can either be a raw format section with no
@@ -64,7 +64,7 @@
   // INDEX MODE ONLY FUNCTIONS AFTER HERE:
   //----------------------------------------------------
 
-#ifndef LLVM_LIBC_SCANF_DISABLE_INDEX_MODE
+#ifndef LIBC_COPT_SCANF_DISABLE_INDEX_MODE
 
   // parse_index parses the index of a value inside a format string. It
   // assumes that str[*local_pos] points to character after a '%' or '*', and
@@ -91,7 +91,7 @@
   // case an O(n^2) operation.
   void args_to_index(size_t index);
 
-#endif // LLVM_LIBC_SCANF_DISABLE_INDEX_MODE
+#endif // LIBC_COPT_SCANF_DISABLE_INDEX_MODE
 };
 
 } // namespace scanf_core
diff --git a/libc/src/stdio/scanf_core/parser.cpp b/libc/src/stdio/scanf_core/parser.cpp
--- a/libc/src/stdio/scanf_core/parser.cpp
+++ b/libc/src/stdio/scanf_core/parser.cpp
@@ -6,7 +6,7 @@
 //
 //===----------------------------------------------------------------------===//
 
-// #define LLVM_LIBC_SCANF_DISABLE_INDEX_MODE 1 // This will be a compile flag.
+// #define LIBC_COPT_SCANF_DISABLE_INDEX_MODE 1 // This will be a compile flag.
 
 #include "src/stdio/scanf_core/parser.h"
 
@@ -22,11 +22,11 @@
 namespace __llvm_libc {
 namespace scanf_core {
 
-#ifndef LLVM_LIBC_SCANF_DISABLE_INDEX_MODE
+#ifndef LIBC_COPT_SCANF_DISABLE_INDEX_MODE
 #define GET_ARG_VAL_SIMPLEST(arg_type, index) get_arg_value<arg_type>(index)
 #else
 #define GET_ARG_VAL_SIMPLEST(arg_type, _) get_next_arg_value<arg_type>()
-#endif // LLVM_LIBC_SCANF_DISABLE_INDEX_MODE
+#endif // LIBC_COPT_SCANF_DISABLE_INDEX_MODE
 
 FormatSection Parser::get_next_section() {
   FormatSection section;
@@ -38,9 +38,9 @@
     ++cur_pos;
     [[maybe_unused]] size_t conv_index = 0;
 
-#ifndef LLVM_LIBC_SCANF_DISABLE_INDEX_MODE
+#ifndef LIBC_COPT_SCANF_DISABLE_INDEX_MODE
     conv_index = parse_index(&cur_pos);
-#endif // LLVM_LIBC_SCANF_DISABLE_INDEX_MODE
+#endif // LIBC_COPT_SCANF_DISABLE_INDEX_MODE
 
     if (str[cur_pos] == '*') {
       ++cur_pos;
@@ -191,7 +191,7 @@
 // INDEX MODE ONLY FUNCTIONS AFTER HERE:
 //----------------------------------------------------
 
-#ifndef LLVM_LIBC_SCANF_DISABLE_INDEX_MODE
+#ifndef LIBC_COPT_SCANF_DISABLE_INDEX_MODE
 
 size_t Parser::parse_index(size_t *local_pos) {
   if (internal::isdigit(str[*local_pos])) {
@@ -219,7 +219,7 @@
   }
 }
 
-#endif // LLVM_LIBC_SCANF_DISABLE_INDEX_MODE
+#endif // LIBC_COPT_SCANF_DISABLE_INDEX_MODE
 
 } // namespace scanf_core
 } // namespace __llvm_libc
diff --git a/libc/src/stdio/scanf_core/scanf_config.h b/libc/src/stdio/scanf_core/scanf_config.h
--- a/libc/src/stdio/scanf_core/scanf_config.h
+++ b/libc/src/stdio/scanf_core/scanf_config.h
@@ -14,11 +14,11 @@
 // This flag disables all functionality relating to floating point numbers. This
 // can be useful for embedded systems or other situations where binary size is
 // important.
-// #define LLVM_LIBC_SCANF_DISABLE_FLOAT
+// #define LIBC_COPT_SCANF_DISABLE_FLOAT
 
 // This flag disables index mode, a posix extension often used for
 // internationalization of format strings. Supporting it takes up additional
 // memory and parsing time, so it can be disabled if it's not used.
-// #define LLVM_LIBC_SCANF_DISABLE_INDEX_MODE
+// #define LIBC_COPT_SCANF_DISABLE_INDEX_MODE
 
 #endif // LLVM_LIBC_SRC_STDIO_SCANF_CORE_SCANF_CONFIG_H
diff --git a/libc/src/stdlib/atexit.cpp b/libc/src/stdlib/atexit.cpp
--- a/libc/src/stdlib/atexit.cpp
+++ b/libc/src/stdlib/atexit.cpp
@@ -28,7 +28,7 @@
   constexpr AtExitUnit(AtExitCallback *c, void *p) : callback(c), payload(p) {}
 };
 
-#ifdef LLVM_LIBC_PUBLIC_PACKAGING
+#ifdef LIBC_COPT_PUBLIC_PACKAGING
 using ExitCallbackList = cpp::ReverseOrderBlockStore<AtExitUnit, 32>;
 #else
 // BlockStore uses dynamic memory allocation. To avoid dynamic memory
@@ -40,7 +40,7 @@
 // deps also (some of which are not yet available in LLVM libc) into the
 // integration tests.
 using ExitCallbackList = FixedVector<AtExitUnit, CALLBACK_LIST_SIZE_FOR_TESTS>;
-#endif // LLVM_LIBC_PUBLIC_PACKAGING
+#endif // LIBC_COPT_PUBLIC_PACKAGING
 
 constinit ExitCallbackList exit_callbacks;
 
diff --git a/libc/src/string/string_utils.h b/libc/src/string/string_utils.h
--- a/libc/src/string/string_utils.h
+++ b/libc/src/string/string_utils.h
@@ -88,7 +88,7 @@
 // Returns the length of a string, denoted by the first occurrence
 // of a null terminator.
 LIBC_INLINE size_t string_length(const char *src) {
-#ifdef LIBC_UNSAFE_STRING_WIDE_READ
+#ifdef LIBC_COPT_UNSAFE_STRING_WIDE_READ
   // Unsigned int is the default size for most processors, and on x86-64 it
   // performs better than larger sizes when the src pointer can't be assumed to
   // be aligned to a word boundary, so it's the size we use for reading the
@@ -143,7 +143,7 @@
 // 'src'. If 'ch' is not found, returns nullptr.
 LIBC_INLINE void *find_first_character(const unsigned char *src,
                                        unsigned char ch, size_t max_strlen) {
-#ifdef LIBC_UNSAFE_STRING_WIDE_READ
+#ifdef LIBC_COPT_UNSAFE_STRING_WIDE_READ
   // If the maximum size of the string is small, the overhead of aligning to a
   // word boundary and generating a bitmask of the appropriate size may be
   // greater than the gains from reading larger chunks. Based on some testing,
diff --git a/libc/src/unistd/getopt.cpp b/libc/src/unistd/getopt.cpp
--- a/libc/src/unistd/getopt.cpp
+++ b/libc/src/unistd/getopt.cpp
@@ -186,7 +186,7 @@
     &impl::optopt, &optpos,
     impl::opterr,  reinterpret_cast<FILE *>(__llvm_libc::stderr)};
 
-#ifndef LLVM_LIBC_PUBLIC_PACKAGING
+#ifndef LIBC_COPT_PUBLIC_PACKAGING
 // This is used exclusively in tests.
 void set_getopt_state(char **optarg, int *optind, int *optopt, unsigned *optpos,
                       int opterr, FILE *errstream) {
diff --git a/libc/test/UnitTest/FPExceptMatcher.h b/libc/test/UnitTest/FPExceptMatcher.h
--- a/libc/test/UnitTest/FPExceptMatcher.h
+++ b/libc/test/UnitTest/FPExceptMatcher.h
@@ -9,7 +9,7 @@
 #ifndef LLVM_LIBC_UTILS_UNITTEST_FPEXCEPTMATCHER_H
 #define LLVM_LIBC_UTILS_UNITTEST_FPEXCEPTMATCHER_H
 
-#ifndef LLVM_LIBC_TEST_USE_FUCHSIA
+#ifndef LIBC_COPT_TEST_USE_FUCHSIA
 
 #include "test/UnitTest/Test.h"
 
@@ -62,6 +62,6 @@
               func)))
 #else
 #define ASSERT_RAISES_FP_EXCEPT(func) ASSERT_DEATH(func, WITH_SIGNAL(SIGFPE))
-#endif // LLVM_LIBC_TEST_USE_FUCHSIA
+#endif // LIBC_COPT_TEST_USE_FUCHSIA
 
 #endif // LLVM_LIBC_UTILS_UNITTEST_FPEXCEPTMATCHER_H
diff --git a/libc/test/UnitTest/Test.h b/libc/test/UnitTest/Test.h
--- a/libc/test/UnitTest/Test.h
+++ b/libc/test/UnitTest/Test.h
@@ -9,7 +9,7 @@
 #ifndef LLVM_LIBC_UTILS_UNITTEST_TEST_H
 #define LLVM_LIBC_UTILS_UNITTEST_TEST_H
 
-#ifdef LLVM_LIBC_TEST_USE_FUCHSIA
+#ifdef LIBC_COPT_TEST_USE_FUCHSIA
 #include "FuchsiaTest.h"
 #else
 #include "LibcTest.h"
diff --git a/libc/test/src/math/RoundToIntegerTest.h b/libc/test/src/math/RoundToIntegerTest.h
--- a/libc/test/src/math/RoundToIntegerTest.h
+++ b/libc/test/src/math/RoundToIntegerTest.h
@@ -84,10 +84,13 @@
   void do_infinity_and_na_n_test(RoundToIntegerFunc func) {
     test_one_input(func, inf, INTEGER_MAX, true);
     test_one_input(func, neg_inf, INTEGER_MIN, true);
-#if LLVM_LIBC_IMPLEMENTATION_DEFINED_TEST_BEHAVIOR
+    // This is currently never enabled, the
+    // LLVM_LIBC_IMPLEMENTATION_DEFINED_TEST_BEHAVIOR CMake option in
+    // libc/CMakeLists.txt is not forwarded to C++.
+#if LIBC_COPT_IMPLEMENTATION_DEFINED_TEST_BEHAVIOR
     // Result is not well-defined, we always returns INTEGER_MAX
     test_one_input(func, nan, INTEGER_MAX, true);
-#endif
+#endif // LIBC_COPT_IMPLEMENTATION_DEFINED_TEST_BEHAVIOR
   }
 
   void testInfinityAndNaN(RoundToIntegerFunc func) {
diff --git a/libc/test/src/stdio/printf_core/parser_test.cpp b/libc/test/src/stdio/printf_core/parser_test.cpp
--- a/libc/test/src/stdio/printf_core/parser_test.cpp
+++ b/libc/test/src/stdio/printf_core/parser_test.cpp
@@ -279,7 +279,7 @@
   ASSERT_PFORMAT_EQ(expected2, format_arr[2]);
 }
 
-#ifndef LLVM_LIBC_PRINTF_DISABLE_INDEX_MODE
+#ifndef LIBC_COPT_PRINTF_DISABLE_INDEX_MODE
 
 TEST(LlvmLibcPrintfParserTest, IndexModeOneArg) {
   __llvm_libc::printf_core::FormatSection format_arr[10];
@@ -474,4 +474,4 @@
   EXPECT_PFORMAT_EQ(expected9, format_arr[9]);
 }
 
-#endif // LLVM_LIBC_PRINTF_DISABLE_INDEX_MODE
+#endif // LIBC_COPT_PRINTF_DISABLE_INDEX_MODE
diff --git a/libc/test/src/stdio/scanf_core/parser_test.cpp b/libc/test/src/stdio/scanf_core/parser_test.cpp
--- a/libc/test/src/stdio/scanf_core/parser_test.cpp
+++ b/libc/test/src/stdio/scanf_core/parser_test.cpp
@@ -549,7 +549,7 @@
   ASSERT_SFORMAT_EQ(expected2, format_arr[2]);
 }
 
-#ifndef LLVM_LIBC_SCANF_DISABLE_INDEX_MODE
+#ifndef LIBC_COPT_SCANF_DISABLE_INDEX_MODE
 
 TEST(LlvmLibcScanfParserTest, IndexModeOneArg) {
   __llvm_libc::scanf_core::FormatSection format_arr[10];
@@ -756,4 +756,4 @@
   EXPECT_SFORMAT_EQ(expected10, format_arr[10]);
 }
 
-#endif // LLVM_LIBC_SCANF_DISABLE_INDEX_MODE
+#endif // LIBC_COPT_SCANF_DISABLE_INDEX_MODE
diff --git a/libc/test/src/stdio/sprintf_test.cpp b/libc/test/src/stdio/sprintf_test.cpp
--- a/libc/test/src/stdio/sprintf_test.cpp
+++ b/libc/test/src/stdio/sprintf_test.cpp
@@ -502,7 +502,7 @@
   ASSERT_STREQ(buff, "0077 01000000000000 002   ");
 }
 
-#ifndef LLVM_LIBC_PRINTF_DISABLE_FLOAT
+#ifndef LIBC_COPT_PRINTF_DISABLE_FLOAT
 
 TEST_F(LlvmLibcSPrintfTest, FloatHexExpConv) {
   __llvm_libc::testutils::ForceRoundingMode r(
@@ -2662,9 +2662,9 @@
   ASSERT_STREQ_LEN(written, buff, "+0.126        0001.26e+03");
 }
 
-#endif // LLVM_LIBC_PRINTF_DISABLE_FLOAT
+#endif // LIBC_COPT_PRINTF_DISABLE_FLOAT
 
-#ifndef LLVM_LIBC_PRINTF_DISABLE_WRITE_INT
+#ifndef LIBC_COPT_PRINTF_DISABLE_WRITE_INT
 TEST(LlvmLibcSPrintfTest, WriteIntConv) {
   char buff[64];
   int written;
@@ -2697,9 +2697,9 @@
   written = __llvm_libc::sprintf(buff, "abc123%n", nullptr);
   EXPECT_LT(written, 0);
 }
-#endif // LLVM_LIBC_PRINTF_DISABLE_WRITE_INT
+#endif // LIBC_COPT_PRINTF_DISABLE_WRITE_INT
 
-#ifndef LLVM_LIBC_PRINTF_DISABLE_INDEX_MODE
+#ifndef LIBC_COPT_PRINTF_DISABLE_INDEX_MODE
 TEST(LlvmLibcSPrintfTest, IndexModeParsing) {
   char buff[64];
   int written;
@@ -2724,4 +2724,4 @@
   EXPECT_EQ(written, 45);
   ASSERT_STREQ(buff, "why would u do this, this is such   a pain. %");
 }
-#endif // LLVM_LIBC_PRINTF_DISABLE_INDEX_MODE
+#endif // LIBC_COPT_PRINTF_DISABLE_INDEX_MODE
diff --git a/utils/bazel/llvm-project-overlay/libc/libc_build_rules.bzl b/utils/bazel/llvm-project-overlay/libc/libc_build_rules.bzl
--- a/utils/bazel/llvm-project-overlay/libc/libc_build_rules.bzl
+++ b/utils/bazel/llvm-project-overlay/libc/libc_build_rules.bzl
@@ -88,7 +88,7 @@
     func_attrs = ["__attribute__((visibility(\"default\")))"]
     if weak:
         func_attrs.append("__attribute__((weak))")
-    local_defines = local_defines or ["LLVM_LIBC_PUBLIC_PACKAGING"]
+    local_defines = local_defines or ["LIBC_COPT_PUBLIC_PACKAGING"]
     local_defines.append("LLVM_LIBC_FUNCTION_ATTR='%s'" % " ".join(func_attrs))
     _libc_library(
         name = name,