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Two dates for the pre-Búzios mailing, Búzios 16 November, and GCC 17 stage 3 the same day

· english· audience: working-cpp· AI-generated, reviewed by Filip Sajdak

Three dates fall within a month of each other, and two land on the same day. I read each one on its primary page on 6 October 2026, and I read the two WG21 pages again on 10 October. None is a forecast: each is published as a fixed date. For the mailing, two WG21 pages give two different dates.

In short

  • Monday 2026-10-19: the pre-Búzios mailing, per the Búzios agenda N5058.
  • Friday 2026-10-23, 15:00 UTC: the pre-Búzios mailing deadline, per a WG21 home page news item.
  • 2026-11-16 to 21: the Búzios meeting, in Rio De Janeiro, Brazil.
  • 2026-11-16: GCC 17 enters stage 3, and new functionality may not be introduced.
  • 2027-03-15 to 20: the Istanbul meeting, the next date for a paper that misses Búzios.

19 or 23 October: the pre-Búzios mailing

Two WG21 pages give two dates for the same mailing.

  • The Búzios agenda, N5058, is dated 2026-09-16. Its mailing list reads “2026-10-19: Monday October 19th, 2026 (pre-Búzios)”, followed by 2026-12-15 for the post-Búzios mailing. It labels the whole list “subject to change”, and the agenda itself is marked a draft.
  • The WG21 home page carries a news item dated 22 September. It gives the deadline for the 2026-10 pre-Búzios mailing as Friday 2026-10-23 15:00 UTC.

The news item is six days newer than the agenda and names a time of day. That makes it the more likely current date. I could not confirm this, and neither page mentions the other. If you are writing a paper for the November meeting, aim for the earlier date, Monday 19 October. The pages do not say what a late paper loses. I did not read the committee’s submission rules, so check those before relying on slack.

16 to 21 November: Búzios

The ISO C++ meetings list gives 2026-11-16 to 21 in Búzios, Rio De Janeiro, Brazil. It does not name a host, and it does not use the word C++29. That comes from Herb Sutter’s report on the June meeting in Brno. The report calls Brno the first meeting of C++29. It says the next full meeting is Búzios, “where we’ll continue adding features to C++29”. Calling Búzios the second C++29 meeting is my reading of those two pages, since nothing sits between them.

Brno adopted these into the C++29 draft, among other things:

  • contracts for virtual functions (P3097R3)
  • designated initializers for base classes (P2287R6)
  • .lookup(key) for associative containers (P3091)

The same report lists two items still in progress. One is a line-by-line telecon review of P3100 on undefined behaviour. The other is a profiles specification from the safety subgroup. What gets voted in is not known.

The meeting after that is 2027-03-15 to 20 in Istanbul. A paper that misses Búzios could reach the room then.

The agenda N5058 gives the week’s shape:

  • Monday starts with the plenary at 8:30 and ends at 4:00 PM, early, for a social event that evening.
  • Tuesday to Friday run from 8:00 to 17:00.
  • Subgroup chairs must have proposals written up as motions by 8:00 PM on Friday.
  • Saturday opens with a plenary at 8:00 that ends no later than 1:30 PM.

The agenda states one goal for the meeting: “Work on C++29 features”. It lists no DIS item and no C++26 item. Its working-draft item is the C++29 draft, N5054.

16 November: GCC 17 stage 3

The GCC development page lists GCC 17 stage 3 starting 2026-11-16 and stage 4 starting 2027-01-18. Stage 1 began on 2026-04-23. The rule for stage 3 allows bug fixes and new ports, and says “New functionality may not be introduced”.

What stage 3 means for you

A contributor with a C++ front-end or library patch should commit it before the 16th. For everyone else, stage 3 is when fixes to trunk stop competing with new features. A bug report against a trunk build is most useful then.

Consider a feature that is only voted into C++29 in Búzios. It could not land in GCC 17 after the vote, because the vote and stage 3 begin together. A patch committed before stage 3 is a different case. I did not check which C++29 papers GCC already implements.

The GCC 17 changes page was last modified on 3 October and is marked a work in progress. It lists no C++ front-end items yet. Under libstdc++ it lists improved experimental C++26 support for two things: std::format in constexpr functions and std::filesystem support for Windows symlinks.

Meeting C++ in Berlin follows on 26 to 28 November and is covered separately.

No demo for this one

A calendar has nothing to run. Every date here comes from a page I read, not from something I executed.

Sources, read on 6 October 2026 unless noted: