# CMAKE\_EXPERIMENTAL\_CXX\_IMPORT\_STD value history and state
**URL:** https://discourse.cmake.org/t/cmake-experimental-cxx-import-std-value-history-and-state/15712
**Category:** Development
**Created:** [June 15, 2026, 7:23am UTC](https://discourse.cmake.org/t/cmake-experimental-cxx-import-std-value-history-and-state/15712 "2026-06-15T07:23:09Z")
**Posts on this page:** 6
**Page:** 1
### Author:  [@ClausKlein](https://discourse.cmake.org/u/ClausKlein)
#### Post date: [June 15, 2026, 7:23am UTC](https://discourse.cmake.org/t/cmake-experimental-cxx-import-std-value-history-and-state/15712/1 "2026-06-15T07:23:09Z")
**AFAIK** , this is are the current rules to activate `import std;` with last stable CMake versions:
```cmake
if(CMAKE_VERSION VERSION_GREATER_EQUAL "3.30.0")
if(CMAKE_VERSION VERSION_LESS "3.31.8")
set(CMAKE_EXPERIMENTAL_CXX_IMPORT_STD
"0e5b6991-d74f-4b3d-a41c-cf096e0b2508"
)
elseif(CMAKE_VERSION VERSION_LESS "4.0.0")
set(CMAKE_EXPERIMENTAL_CXX_IMPORT_STD
"d0edc3af-4c50-42ea-a356-e2862fe7a444"
)
elseif(CMAKE_VERSION VERSION_LESS "4.0.3")
set(CMAKE_EXPERIMENTAL_CXX_IMPORT_STD
"a9e1cf81-9932-4810-974b-6eccaf14e457"
)
elseif(CMAKE_VERSION VERSION_LESS "4.3.0")
set(CMAKE_EXPERIMENTAL_CXX_IMPORT_STD
"d0edc3af-4c50-42ea-a356-e2862fe7a444"
)
elseif(CMAKE_VERSION VERSION_LESS "4.4.0")
set(CMAKE_EXPERIMENTAL_CXX_IMPORT_STD
"451f2fe2-a8a2-47c3-bc32-94786d8fc91b"
)
endif()
endif()
```
- Is it really necessary to change the **UUID** in this way?
- What is planed to be the right value for `CMake v4.4.0?`
- I wonder if a **UUID** value from the `experimental gate` must be changed at all?
---
### Author:  [@ben.boeckel](https://discourse.cmake.org/u/ben.boeckel)
#### Post date: [June 15, 2026, 1:31pm UTC](https://discourse.cmake.org/t/cmake-experimental-cxx-import-std-value-history-and-state/15712/2 "2026-06-15T13:31:06Z")
Anytime we change the behavior of the experimental feature, the UUID is recycled. This is because behavior changes can break existing code, contrary to CMake’s typical compatibility guarantees.
I’m not aware of any pending changes that would change 4.4’s UUID, but that doesn’t mean we won’t fix bugs (and change the UUID in the process) if they come up.
---
### Author:  [@ClausKlein](https://discourse.cmake.org/u/ClausKlein)
#### Post date: [July 6, 2026, 6:47pm UTC](https://discourse.cmake.org/t/cmake-experimental-cxx-import-std-value-history-and-state/15712/3 "2026-07-06T18:47:02Z")
update:
```cmake
# SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
if(CMAKE_VERSION VERSION_GREATER_EQUAL "4.4.0")
set(CMAKE_EXPERIMENTAL_CXX_IMPORT_STD
"f35a9ac6-8463-4d38-8eec-5d6008153e7d"
)
elseif(CMAKE_VERSION VERSION_GREATER_EQUAL "4.3.0")
set(CMAKE_EXPERIMENTAL_CXX_IMPORT_STD
"451f2fe2-a8a2-47c3-bc32-94786d8fc91b"
)
elseif(CMAKE_VERSION VERSION_GREATER_EQUAL "3.30.0")
if(CMAKE_VERSION VERSION_LESS "3.31.8")
set(CMAKE_EXPERIMENTAL_CXX_IMPORT_STD
"0e5b6991-d74f-4b3d-a41c-cf096e0b2508"
)
elseif(CMAKE_VERSION VERSION_LESS "4.0.0")
set(CMAKE_EXPERIMENTAL_CXX_IMPORT_STD
"d0edc3af-4c50-42ea-a356-e2862fe7a444"
)
elseif(CMAKE_VERSION VERSION_LESS "4.0.3")
set(CMAKE_EXPERIMENTAL_CXX_IMPORT_STD
"a9e1cf81-9932-4810-974b-6eccaf14e457"
)
elseif(CMAKE_VERSION VERSION_LESS "4.3.0")
set(CMAKE_EXPERIMENTAL_CXX_IMPORT_STD
"d0edc3af-4c50-42ea-a356-e2862fe7a444"
)
endif()
endif()
```
---
### Author:  [@HodarinS](https://discourse.cmake.org/u/HodarinS)
#### Post date: [September 22, 2026, 9:58am UTC](https://discourse.cmake.org/t/cmake-experimental-cxx-import-std-value-history-and-state/15712/4 "2026-09-22T09:58:54Z")
Why not make a simpler way to enable experimental features, for example `set(CMAKE_EXPERIMENTAL_CXX_IMPORT_STD ON)`?
---
### Author:  [@leha-bot](https://discourse.cmake.org/u/leha-bot)
#### Post date: [September 23, 2026, 9:06am UTC](https://discourse.cmake.org/t/cmake-experimental-cxx-import-std-value-history-and-state/15712/5 "2026-09-23T09:06:11Z")
There is an issue about dropping these magic uuids completely as the feature itself had already grown maturely: [https://gitlab.kitware.com/cmake/cmake/-/work\_items/28014](https://gitlab.kitware.com/cmake/cmake/-/work_items/28014) - but it’s not clear abour 4.5 time frame (it is scheduled on the October)
---
### Author:  [@brad.king](https://discourse.cmake.org/u/brad.king)
#### Post date: [September 23, 2026, 12:08pm UTC](https://discourse.cmake.org/t/cmake-experimental-cxx-import-std-value-history-and-state/15712/6 "2026-09-23T12:08:27Z")
> [@HodarinS](#):
>
> Why not make a simpler way to enable experimental features, for example `set(CMAKE_EXPERIMENTAL_CXX_IMPORT_STD ON)`?
From `Help/dev/experimental.rst`:
> the specific values will change over time to reinforce their experimental nature.
As an experimental feature develops, breaking changes are allowed and come with a UUID update. In order for people trying it to distinguish between “this experimental feature doesn’t work” and “this project isn’t aware of a breaking change”, a project must explicitly specify the UUID of which it is aware.