Added

• Added Player.sequences as the collection of sequences available to a player.
• Implement GameSubgameRep (C++) and Subgame (Python), a first-class object representing a subgame. (#585)
• Games can be materialised directly from OpenSpiel games if pyspiel is installed. (#917)
• Magnify events are now supported in GUI for zooming in/out on trees.

Fixed

• Corrected resizing of row and column index labels in strategic form so pivoting works correctly. (#844)
• Corrected incorrect output of strategic game tables to .nfg files if strategies have previously been
  deleted in the game (#875)
• Fix incorrect row index checking in swapping rows of a rectangular array (leading to errors in
  for example simpdiv_solve) (#868)
• In GUI, typing a payoff with a trailing slash is now interpreted as a whole number
  (previously this led to a validation error dialog)
• Improved initial zoom and centering of display of game trees on initial load, and focusing behavior
  on currently-selected node or jumping to the root. Also adjusted the initial size of the
  game window to a more comfortable size. (#569)
• In the GUI, tab-traversal on tables (such as the strategic form payoff table) now works
  as expected (TAB moves one cell to the right, wrapping if appropriate; SHIFT-TAB moves
  to the left, wrapping if appropriate).
• Max regret is calculated correctly for strategy and behavior profiles on games with zero player
  strategies or actions (is defined to be 0 trivially) (#904)
• Corrected calculation of total number of actions for a player in pygambit (#938)
• Corrected a regression in action graph games that left the internal data structure not fully initialised,
  leading to segmentation faults.
• Corrected handling of malformed AGG/BAGG files: files with an invalid or degenerate header
  (for example a wrong file type, or a header declaring zero players) are now rejected with a
  ValueError instead of causing a segmentation fault while constructing the game.

Changed

• Added a new welcome/landing window on launching the GUI without a game. This has the effect of
  avoiding creating a window with a trivial extensive game which the user then has to dismiss if
  they do not require it. (#80)
• Clarified handling of .efg/.nfg/.gbt file types in graphical interface and refined warnings about
  unsaved work. (#12)
• Created and documented right-click context menu in the normal form pivot table, which makes the
  mechanism for deleting a strategy more clear. (#855)
• Payoff editing in extensive games in the graphical interface is now done via a context popup window
  rather than text controls drawn (not always well!) over the game tree display. (#947)
• In pygambit, indexing game object collections by integer position has been removed. (#942)
• Validity of game object labels is enforced (printable ASCII and spaces only, no leading/trailing or
  double spaces); invalid labels raise ValueError in pygambit. (#944)
• Nonempty labels are now required for all players, outcomes, actions, and strategies.
  Labels must be unique within the game for players and outcomes, within the player for
  strategies, and within the information set for actions.
• Refined and clarified the graphical interface's handling (and persisting) of "workspaces", and
  improved warning messages on closing windows for games or workspaces with unsaved changes.
• In pygambit, the .outcome, .player, and .infoset attributes are now treated as predicates
  that are evaluated on-demand, to align with the behaviour of collections. (#946)

Removed

• Built-in plotting of logit QRE for strategic games has been removed in the GUI (#809)

[16.6.0] - 2026-03-24

Changed

• Gambit has a refreshed branding and logo which is reflected in this release!
• Game.comment has been renamed to Game.description
• With behaviour profiles that reach some information sets with probability zero, beliefs, action
  values, and infoset values are not well-defined. These functions now return a
  std::optional in C++ and type or None in Python, where nulls indicate these quantities
  are not defined. (#446)

Added

• Implement linear-time algorithm to find all root nodes of proper subgames, using an adaptation of
  Tarjan's (1974) algorithm for finding bridges in an undirected graph. Subgame roots are cached so
  subsequent lookup is constant-time (if the game is unchanged). (#584)

Fixed

• enumpoly would take a very long time on some supports where an equilibrium is located on the
  boundary of the projected game. Search is now restricted to the interior of the space ruling
  these out; these will always be found by another projection. (#756)
• In the graphical interface, the logit correspondence display would fail and terminate the program
  on very small (<10^{-300}) probabilities.
• The new subgame root computation fixes a bug which failed to detect subgames where the subgame
  root node is a member of an absent-minded infoset. (#584)
• Removed spurious warning in graphical interface when loading file as a command-line argument
  (or also by clicking on a file in MSW, as that uses the command-line mechanism). (#801)
• Game.reveal raised a null pointer access exception or dumped core in some cases (#749)

Fixed

• Sequence-form based equilibrium-finding methods returned incorrect output on games with
  outcomes at non-terminal nodes. (#654)

Added

• Implement IsAbsentMinded() on information sets (C++) and Infoset.is_absent_minded (Python)
  to detect if an information is absent-minded.
• Tests for EFG Nash solvers -- enumpoly_solve, lp_solve, lcp_solve -- in behavior strategies
• In pygambit, Node objects now have a read-only property own_prior_action and Infoset objects
  have a read-only property own_prior_actions to retrieve the last action or the set of last actions
  taken by the player before reaching the node or information set, respectively. (#582)
• In pygambit, Node objects now have a read-only property is_strategy_reachable to determine
  if the node is reachable by at least one pure strategy profile. This proves useful for identifying
  unreachable parts of the game tree in games with absent-mindedness. (#629)

Changed

• Labels for players, outcomes, strategies, and actions are expected to be non-empty and unique within
  the relevant scope (games for players and outcomes, players for strategies, and information sets for
  actions). pygambit now issues a FutureWarning if a label is changed that does not conform to these
  expectations. There is now an optional flag normalize_labels to read_* which will automatically
  fill in non-confirming sets of labels. In version 16.6 these will be enforced; invalid label sets will
  generate an error and files will be normalized automatically on read. (#614)
• Terminology for agent-form calculations on extensive games has been clarified. Mixed behavior profiles
  distinguish "agent" regret and liap values from their strategy-based analogs. Methods which compute
  using the agent-form - specifically enumpure_solve and liap_solve, now clarify this by being named
  differently in pygambit. (#617)
• For clarity, the stop_after and max_depth arguments to lcp_solve are no longer permitted when solving using
  the sequence form. These actually had no effect in previous versions. (#671)
• In the graphical interface, removed option to configure information set link drawing; information sets
  are always drawn and indicators are always drawn if an information set spans multiple levels.
• In pygambit, indexing the children of a node by a string inteprets the string as an action label,
  not a label of a child node. In addition, indexing by an action object is now supported. (#587)
• In pygambit, min_payoff and max_payoff (for both games and players) now refers to payoffs in
  any play of the game; previously this referred only to the set of outcomes. (#498)
• In pygambit, calls to sort_infosets are no longer required to normalise the game representation.
  Iteration ordering of information sets and their members is ensured internally. sort_infosets
  is therefore now a no-op and is deprecated; it will be removed in a future version.

Removed

• Eliminating dominated actions has been removed from the GUI as it was implementing a non-standard
  formulation of dominance. (#612)
• The C++ method for computing subgame perfect equilibria with selected methods has been removed
  (and as a result from the enumpure, lp, and lcp command-line tools); this will be replaced
  with new and more customisable approaches. (#639)

Fixed

• Fixed a regression in which null outcomes in strategic game tables were not handled correctly
  when changing the number of strategies in the game (#571)
• Fixed improper shared pointer handling when writing a .nfg file based on a game in
  extensive form.
• Fixed a regression in the GUI in which unique action labels were not being generated when
  adding a move via drag-and-drop of a player icon (#618)
• Fixed a regression generating null pointer dereference errors when setting the outcome of
  a node to the null outcome (#625, #647)
• Fixed a regression in calculating payoff quantities for mixed strategy profiles derived from
  mixed behavior profiles (#616)

Fixed

• Parsing of output of gambit-logit in the graphical interface did not handle the
  terminal Nash profile correctly. (#172)
• Improved sizing of list of logit profiles computed for normal form games.

Changed

• Removed Ctrl/Cmd-X accelerator for closing program, as this clashes with modern standard
  expectations. (#507)

Removed

• Undo and redo have been removed from the graphical interface. (These were meant to be
  removed previously as they did not work properly and gave unpredictable behaviour.) (#505)

General

• Officially added support for Python 3.13.
• For graphical interface, added support for wxWidgets 3.3; require minimum of wxWidgets 3.2.

Removed

• The deprecated functions Game.read_game, Game.parse_game and Game.write functions have
  been removed as planned. (#357)

Added

• Implement GetPlays() (C++) and get_plays (Python) to compute the set of terminal nodes consistent
  with a node, information set, or action (#517)
• Implement GameStrategyRep::GetAction (C++) and Strategy.action (Python) retrieving the action
  prescribed by a strategy at an information set
• Tests for creation of the reduced strategic form from an extensive-form game (currently only
  for games with perfect recall)
• Implement Nodes collection as a member of GameRep, including a C++ iterator that
  returns nodes in depth-first traversal order (#530)

Changed

• Internally in C++ std::shared_ptr are now used to manage memory allocated for game objects. (#518)
• The iteration order of a player's information sets, and of the members of an information set, now may
  depend on the order of operations to build a game tree. The previous behaviour - ensuring sorting
  by the order encountered in a depth-first traversal of the tree - can now be obtained by calling
  SortInfosets (C++) or sort_infosets (Python) on the game. (#483)

Fixed

• Corrected a regression in which information sets were prematurely invalidated (and therefore
  delete this called on them) when removing the last node from an information set.
• Game.copy_tree and Game.move_tree implementations reversed the roles of the
  src and dest nodes (#499)

Changed

• For graphical interface, added support for wxWidgets 3.3; require minimum of wxWidgets 3.2.

Fixed

• Game.copy_tree and Game.move_tree implementations reversed the roles of the
  src and dest nodes (#499)

Changed

• For graphical interface, added support for wxWidgets 3.3; require minimum of wxWidgets 3.2.

General

• Dropped support for Python 3.8.

Added

• Implemented maximum-likelihood estimation for agent logit QRE, to parallel existing support
  for strategic logit QRE. Strategic logit QRE function names have been modified to provide
  parallel naming. Estimation using the correspondence now supports an option to stop at the
  first interior local maximizer found (if one exists).
• Maximum-likelihood estimation for logit QRE using empirical payoffs has an improved internal
  calculation of log-likelihood, and returns the estimated profile instead of just a list of
  probabilities.
• Reorganized naming conventions in pygambit for functions for computing QRE in both strategic
  and agent versions, and added a corresponding section in the user guide.
• enumpoly_solve has been returned to being fully supported from temporarily being experimental;
  now available in pygambit.
• enumpoly_solve for strategic games now uses the Porter, Nudelman, and Shoham (2004) ordering
  of supports to search.
• to_arrays converts a Game to a list of numpy arrays containing its reduced strategic form.
  (#461)
• Integrated support (in Python) for using PHCpack to solve systems of polynomial equations in
  enumpoly_solve based on an implementation formerly in the contrib section of the
  repository. (#165)
• New format-specific functions pygambit.read_* and pygambit.Game.to_* functions have been
  added to (de-)serialise games. The existing Game.read_game and Game.write functions have
  been deprecated and will be removed in 16.4. (#357)

Changed

• The built-in implementation of lrslib (dating from 2016) has been removed. Instead, access to
  lrsnash is provided as an external tool via the enummixed_solve function, in parallel to
  PHCpack for enumpoly_solve.

Fixed

• When parsing .nfg files, check that the number of outcomes or payoffs is the expected number,
  and raise an exception if not. (#119)

Removed

• Game.write() no longer supports generation of the XML-format files for Game Theory
  Explorer, as GTE no longer reads files in this format.

Fixed

• Corrected an internal implementation error in Game.reveal() in resolving references to
  information sets and players (#453)
• Reading .efg and .nfg game files which did not have whitespace at the end would lead to
  an infinite loop (#457)
• Attempting to call the default constructor on Game objects (rather than one of the factory
  functions) now raises a more informative exception (#463)