Does V8 now allow C++20?

[Ho Cheung]

I am planning to make some C++20 related contributions to V8. Is V8 allowed to use C++20 now?

[Ronald Fenner]

They probably use what chromium uses and I've seen a concept used in the gin framework which is a c++20 feature so they probably do but they can confirm for sure.

[Clemens Backes]

Yes, V8 allows the use of C++ language and library features since ~two weeks (https://crrev.com/c/5587859). Note though that GCC and MSVC do not always agree with clang on what's valid C++20. See Hannes' mails on reducing support for those compilers.

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[Ho Cheung]

OK thanks

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[James Dennett]

Now that Chromium allows (some) use of C++23 features, is there a plan/policy/path to doing the same in V8?  Is this documented anywhere?  (My Google-fu has failed me, if so.)

Given that this is something of a balancing act between the benefit to V8 developers and the needs of V8 integrators ("users"), is this decision made in approximately the same way for each C++ update?  Would it be a reasonable approximation to guess that V8 might break C++20 compatibility around three years after requiring it (and breaking C++17 compatibility), which would put this around June 2027, or is there a realistic chance that it might happen much faster for C++23 than for C++20?

-- James

[Jakob Kummerow]

I don't think there's a timeline for C++23 in V8 yet. For the time being, V8 is still on C++20.

I wouldn't expect that the schedule necessarily matches previous C++ version rollouts. New C++ versions are relatively infrequent and each is different, so it's a case-by-case decision, driven by factors such as: 

- Does the new C++ version offer anything that we'd want to use?

- Does switching require any extra work, and when can we prioritize that work?

- Are there any blocking concerns from embedders?

We are well aware of the balancing act. Right now for C++23, I think we want to give embedders a bit more time, but I don't know how much time that might be.

Is there a particular reason for your question?

[James Dennett]

On Fri, Apr 10, 2026 at 2:18 AM Jakob Kummerow <jkum...@chromium.org> wrote:

I don't think there's a timeline for C++23 in V8 yet. For the time being, V8 is still on C++20.

I wouldn't expect that the schedule necessarily matches previous C++ version rollouts. New C++ versions are relatively infrequent and each is different, so it's a case-by-case decision, driven by factors such as: 

- Does the new C++ version offer anything that we'd want to use?

- Does switching require any extra work, and when can we prioritize that work?

- Are there any blocking concerns from embedders?

We are well aware of the balancing act.

I had assumed as much, yes!

 

Right now for C++23, I think we want to give embedders a bit more time, but I don't know how much time that might be.

Is there a particular reason for your question?

Beyond curiosity, this is useful for planning as an embedder of V8 and a potential contributor to the V8 codebase.

As an embedder of V8, we need to ensure that we have C++23-compatible builds of other dependencies (including other open source projects) before V8 makes it a hard requirement, as well as updates to tools, policies, etc. as are always needed for C++ version updates.  We may need to contribute patches to other libraries for C++23 compatibility, depending on the timeline.

-- James