Erlang OTP 27.0 Released

Erlang/OTP 27 Released

All artifacts for the release can be downloaded from the Erlang/OTP Github release and you can view the new documentation at

You can also install the latest release using kerl like this:

kerl build 27.0 27.0

The new Erlang/OTP 27 release contains new features, improvements as well as a few incompatibilities. Some of the new features are highlighted below.

Many thanks to all contributors!


EEP-59 has been implemented. Documentation attributes in source files can now be used to document functions, types, callbacks, and modules.

The entire Erlang/OTP documentation is now using the new documentation system.

New language features

  • Triple-Quoted Strings has been implemented as per EEP 64 to allow a string to encompass a complete paragraph.

  • Adjacent string literals without intervening white space is now a syntax error, to avoid possible confusion with triple-quoted strings.

  • Sigils on string literals (both ordinary and triple-quoted) have been implemented as per EEP 66. For example, ~"Björn" or ~b"Björn" are now equivalent to <<"Björn"/utf8>>.

Compiler and JIT improvements

  • The compiler will now merge consecutive updates of the same record.

  • Safe destructive update of tuples has been implemented in the compiler and runtime system. This allows the VM to update tuples in-place when it is safe to do so, thus improving performance by doing less copying but also by producing less garbage.

  • The maybe expression is now enabled by default, eliminating the need for enabling the maybe_expr feature.

  • Native coverage support has been implemented in the JIT. It will automatically be used by the cover tool to reduce the execution overhead when running cover-compiled code. There are also new APIs to support native coverage without using the cover tool.

  • The compiler will now raise a warning when updating record/map literals to catch a common mistake. For example, the compiler will now emit a warning for #r{a=1}#r{b=2}.

  • The order in which the compiler looks up options has changed.

    When there is a conflict in the compiler options given in the -compile() attribute and options given to the compiler, the options given in the -compile() attribute overrides the option given to the compiler, which in turn overrides options given in the ERL_COMPILER_OPTIONS environment variable.


    If some_module.erl has the following attribute:


    and the compiler is invoked like so:

    % erlc +warn_missing_spec some_module.erl

    no warnings will be issued for functions that do not have any specs.


  • The erl command now supports the -S flag, which is similar to the -run flag, but with some of the rough edges filed off.

  • By default, escripts will now be compiled instead of interpreted. That means that the compiler application must be installed.

  • The existing experimental support for archive files will be changed in a future release. The support for having an archive in an escript will remain, but the support for using archives in a release will either become more limited or completely removed.

    As of Erlang/OTP 27, the function code:lib_dir/2, the -code_path_choice flag, and using erl_prim_loader for reading members of an archive are deprecated.

    To remain compatible with future version of Erlang/OTP escript scripts that need to retrieve data files from its archive should use escript:extract/2 instead of erl_prim_loader and code:lib_dir/2.

  • The default process limit has been raised to 1048576 processes.

  • The erlang:system_monitor/2 functionality is now able to monitor long message queues in the system.

  • The obsolete and undocumented support for opening a port to an external resource by passing an atom (or a string) as first argument to open_port(), implemented by the vanilla driver, has been removed. This feature has been scheduled for removal in OTP 27 since the release of OTP 26.

  • The pid field has been removed from erlang:fun_info/1,2.

  • Multiple trace sessions are now supported.

  • configure now automatically enables support for year-2038-safe timestamps.

    By default configure scripts used when building OTP will now try to enable support for timestamps that will work after mid-January 2038. This has typically only been an issue on 32-bit platforms. If configure cannot figure out how to enable such timestamps, it will abort with an error message. If you want to build the system anyway, knowing that the system will not function properly after mid-January 2038, you can pass the --disable-year2038 option to configure, which will enable configure to continue without support for timestamps after mid-January 2038.’


  • There is a new module json for encoding and decoding JSON.

    Both encoding and decoding can be customized. Decoding can be done in a SAX-like fashion and handle multiple documents and streams of data.

    The new json module is used by the jer (JSON Encoding Rules) for ASN.1 for encoding and decoding JSON. Thus, there is no longer any need to supply an external JSON library.

  • Several new functions that accept funs have been added to module timer.

  • The functions is_equal/2, map/2, and filtermap/2 have been added to the modules sets, ordsets, and gb_sets.

  • There are new efficient ets traversal functions with guaranteed atomicity. For example, ets:next/2 followed by ets:lookup/2 can now be replaced with ets:next_lookup/1.

  • The new function ets:update_element/4 is similar to ets:update_element/3, but takes a default tuple as the fourth argument, which will be inserted if no previous record with that key exists.

  • binary:replace/3,4 now supports using a fun for supplying the replacement binary.

  • The new function proc_lib:set_label/1 can be used to add a descriptive term to any process that does not have a registered name. The name will
    be shown by tools such as c:i/0 and observer, and it will be included in crash reports produced by processes using gen_server, gen_statem, gen_event, and gen_fsm.

  • Added functions to retrieve the next higher or lower key/element from gb_trees and gb_sets, as well as returning iterators that start at given keys/elements.


  • Calls to ct:capture_start/0 and ct:capture_stop/0 are now synchronous to ensure that all output is captured.

  • The default CSS will now include a basic dark mode handling if it is preferred by the browser.


  • The functions crypto_dyn_iv_init/3 and crypto_dyn_iv_update/3 that were marked as deprecated in Erlang/OTP 25 have been removed.


  • The --gui option for Dialyzer has been removed.


  • The ssl client can negotiate and handle certificate status request (OCSP stapling support on the client side).


  • There is a new tool tprof, which combines the functionality of eprof and cprof under one interface. It also adds heap profiling.


  • As an alternative to xmerl_xml, a new export module xmerl_xml_indent that provides out-of-the box indented output has been added.

For more details about new features and potential incompatibilities see the README.


Hooray for process labels :tada:


What a release. And it’s like an Elixirification of Erlang: they are using ExDoc for Erlang’s docs, added sigils and heredocs and new :json module in the stdlib.


Congratulations on the release and also to the ExDoc team who’ve paved the way for the new (much improved) Erlang docs. A bit fun that there’s now Elixir code in the main OTP repository.


Fantastic to see a native JSON encoder/decoder, hopefully it will trickle down into different Elixir projects soon :slight_smile:


Wow, I love the new docs!