We present SemEval-2026 Task 1: MWAHAHA (Models Write Automatic Humor And Humans Annotate), the first shared task on general-purpose humor generation. Systems must produce short jokes in English, Spanish, and Chinese under lexical or topical constraints (Subtask A) and generate humorous captions for GIFs (Subtask B). To discourage memorization and ensure fairness, all jokes must meet specific criteria, such as using infrequent word pairs or relating to recent news headlines. Evaluation is conducted through pairwise human preference judgments in a Chatbot Arena-style setting, yielding Elo-based rankings. The task attracted 309 registered users, with 37 teams submitting systems to the evaluation phase. Participating systems employ a wide range of NLP techniques, including generate-then-rank pipelines, reinforcement learning, parameter-efficient fine-tuning, retrieval-augmented generation, humor-theory-grounded prompting, and persona-based strategies. Our Gemini 2.5 Flash baseline, using simple prompts, tied for first place in all subtasks, and the majority of elaborate multi-stage pipelines only marginally surpassed it with overlapping confidence intervals. More work is necessary to outperform the simple usage of state-of-the-art large language models. We release all evaluation data, prompts, and leaderboard results to support future research in computational humor generation.