# GCC 16 Release Series
Changes, New Features, and Fixes

This page is a "brief" summary of some of the huge number of improvements in GCC 16.

Note: GCC 16 has not been released yet, so this document is a work-in-progress.

## Caveats

- ...

## General Improvements

## New Languages and Language specific improvements

### OpenMP

See the GNU Offloading and Multi-Processing Project (GOMP) page for general information.

- OpenMP 5.2: The `begin declare variant` directive for C and C++ is now supported.
- OpenMP 6.0: The `omp_target_memset` and `omp_target_memset_async` API routines have been added.

### OpenACC

See the GCC OpenACC wiki page for general information.

- The `acc_memcpy_device` and `acc_memcpy_device_async` API routines have been added for C, C++ and Fortran.
- OpenACC 3.0: The `wait` directive now accepts the `if` clause.
- OpenACC 3.3: The Fortran API routines `acc_attach` and `acc_detach` now augment their OpenACC 2.6 C/C++ counterparts.
- OpenACC 3.4: In Fortran, named constants (`PARAMETER`) used as var in data clauses are now permitted by the specification and GCC for better compatibility with existing code; however, with GCC, specifying them in data clauses affects neither compile-time nor runtime behavior.

### C++

#### Runtime Library (libstdc++)

- For targets that support 128-bit integers, `std::is_integral<__int128>` and similar traits are always true. Previously this was only the case when compiling with GNU dialects (`-std=gnu++17`, `-std=gnu++14`, etc.) and not with strict dialects (`-std=c++17`, etc.)
- Improved experimental support for C++20, including:
  - Working `std::chrono::current_zone()` on Windows (thanks to Björn Schäpers).
- There are several changes to C++20 components which are incompatible with the experimental C++20 support in previous releases. The following C++20 components have ABI changes in GCC 16:
  - Atomic waiting/notifying functions in `<atomic>` and semaphore types in `<semaphore>`. Synchronization for `<syncstream>`.
  - The representation of `std::format` args and `std::formatter` specializations.
  - The representation of the `std::partial_ordering` type in `<compare>`.
  - Semantics of `std::variant` with `std::jthread`, `std::stop_token`, and `std::stop_source` alternatives.
  - Representation of some range adaptors in `<ranges>`.
  . This list is not necessarily complete. As with all experimental support, programs using C++20 components should assume that those components are not compatible between different major releases.
- Improved experimental support for C++23, including:
  - `std::mdspan`, thanks to Luc Grosheintz.
  - `ranges::starts_with` and `ranges::ends_with`.
- Improved experimental support for C++26, including:
  - `std::inplace_vector`.
  - `std::copyable_function` and `std::function_ref`.
  - `std::indirect` and `std::polymorphic`.
  - `std::owner_equal` for shared pointers, thanks to Paul Keir.
  - `<debugging>` header and contents.
  - New `std::stringstream` and `std::bitset` member functions accepting `std::string_view` arguments, thanks to Nathan Myers.
  - Padded mdspan layouts, aligned accessor, and `std::dims`, thanks to Luc Grosheintz.

### Fortran

- Coarray improvements, especially for handling Fortran 2018's `TEAM` feature.
- Fortran 2018: Support the extensions to the `IMPORT` statement and the new `GENERIC` statement.
- The Fortran 2023 additions to the trigonometric functions are now supported (such as the `sinpi` intrinsic).
- Fortran 2023: The `split` intrinsic subroutine is now supported and `c_f_pointer` now accepts an optional lower bound as a argument.
- The `-fexternal-blas64` option has been added to call external BLAS routines with 64-bit integer arguments for `MATMUL`. This option is only valid for 64-bit systems and when `-ffrontend-optimize` is in effect.

## New Targets and Target Specific Improvements

### IA-32/x86-64

- The new `--enable-x86-64-mfentry` configure option enables `-mfentry` which uses `__fentry__`, instead of `mcount` for profiling on x86-64. This option is enabled by default for glibc targets.
- `--enable-tls=DIALECT` is now supported to control the default TLS dialect. The default remains `gnu`. The accepted values are `gnu` and `gnu2` (for TLS descriptors).

### AMD GPU (GCN)

- Experimental support for AMD Instinct MI300 (`gfx942`) devices has been added, including the generic `gfx9-4-generic` and mostly compatible `gfx950`.
- By default, the following multilibs are now built: `gfx908`, `gfx90a`, `gfx9-generic`, `gfx9-4-generic`, `gfx10-3-generic`, and `gfx11-generic`. Multilibs for specific devices are no longer built by default if a generic arch exists. Note:
  - When compiling for a specific arch and the multilib only exists for the associated generic arch, GCC's error message suggests the command-line option to do so.
  - Generic architectures require ROCm 6.4.0 or newer.
  - The new default-built set of multilibs now requires the assembler and linker of LLVM 19 or newer.
  - Consult GCC's AMD installation notes and configuration notes for setting the multilibs to be build.

### S/390, System z, IBM z Systems

- Bit-precise integer types (`_BitInt (N)` and `unsigned _BitInt (N)`) are supported, now.
- Global stack protector support has been added and exported via `-mstack-protector-guard=global`. Option `-mstack-protector-guard-record` was added, too. The primary use is for the Linux kernel in order to support run-time patching of the address loading of the canary.

## Operating Systems

## Other significant improvements

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These pages are maintained by the GCC team. Last modified 2025-11-28.