"Agents Can Learn Covert Communication at Test Time Without Explicit Negotiation" AI agents can learn a secret language at test time without fine-tuning, a codebook, or explicit negotiation. In each round, one agent saw a private value and sent an ordinary task update, while the other tried to infer the secret. They only learned whether the guess was correct. From this 1-bit feedback alone, GPT-5.6 Sol agents gradually learned which subtle wording patterns mapped to which secrets, reaching…