The new penalty guides cover this. I'll quote some relevant sections.
The Golden Rule of Player Communication: Statements made about the game being played must be truthful (to the best of their knowledge). However, statements do not need to be exhaustive – honest answers with careful omissions or “non-answers” designed to misdirect opponents into making suboptimal – but not illegal – plays are acceptable.
The following areas are exceptions to the Golden Rule:
Statements about hidden information do not need to be true in any way. Bluffs involving the content of that hidden information are an integral part of the game.
Statements about a future game state or future action are not required to be true. Whether this statement could be true in the future is irrelevant.
Players are responsible for ensuring that the physical state of the game (tapped status, flipped status, the zone an object is in) is clear at all times.
If a player asks their opponent a question, the opponent usually can decline to answer. If they do choose to answer, then they are expected to adhere to the Golden Rule.
layers must answer completely and honestly specific questions about past game actions taken since the active player's previous turn.
Players must answer completely and honestly specific questions about the game state that cannot be derived from physical representations and/or game actions taken since the active player’s previous turn.
If a player does not wish to ask their opponent a question or does not believe they have received the information that they need, they are encouraged to call a judge. Players may not decline to answer questions asked of them by a judge (and their answers must be truthful and complete), but they may ask to answer away from the table.
Players are responsible for being aware of the game state. Judges will not generally assist the player in determining the current game state but can answer questions about the rules, interactions between cards, or the Oracle texts of relevant cards. At Regular REL, the judge may assist the players in understanding the game state in the interest of education.
Players may not use misleading statements to trick their opponent into making illegal plays. Players may not misrepresent to the opponent that an illegal play has occurred.
You only have to be honest about the current game.
