From gnu:

https://gcc.gnu.org/ml/gcc-announce/2016/msg00000.html

After slightly more than a year since last major GCC release, we are proud
to announce new major GCC release, 6.1.

GCC 6.1 is a major release containing substantial new
functionality not available in GCC 5.x or previous GCC releases.

The C++ frontend now defaults to C++14 standard instead of C++98 it has
been defaulting to previously, for compiling older C++ code that might
require either explicitly compiling with selected older C++ standards,
or might require some code adjustment, see
http://gcc.gnu.org/gcc-6/porting_to.html for details.  The experimental
C++17 support has been enhanced in this release.

This releases features various improvements in the emitted diagnostics,
including improved locations, location ranges, suggestions for misspelled
identifiers, option names etc., fix-it hints and a couple of new warnings
have been added.

The OpenMP 4.5 specification is fully supported in this new release, the
compiler can be configured for OpenMP offloading to Intel XeonPhi Knights
Landing and AMD HSAIL.  The OpenACC 2.0a specification support has been
much improved, with offloading to NVidia PTX.

The optimizers have been improved, with improvements appearing in all of
intra-procedural optimizations, inter-procedural optimizations,
link time optimizations and various target backends.

See

  https://gcc.gnu.org/gcc-6/changes.html

for more information about changes in GCC 6.1.

This release is available from the FTP servers listed here:

 http://www.gnu.org/order/ftp.html

The release is in gcc/gcc-6.1.0/ subdirectory.

If you encounter difficulties using GCC 6.1, please do not contact me
directly.  Instead, please visit http://gcc.gnu.org for information
about getting help.

Driving a leading free software project such as GNU Compiler Collection
would not be possible without support from its many contributors.
Not to only mention its developers but especially its regular testers
and users which contribute to its high quality.  The list of individuals
is too large to thank individually!