## TL;DR
AI plans your vacation -- from LLMs generating personalized itineraries to Hopper predicting the best time to book flights. Google, Expedia, and Booking.com have all launched conversational AI trip planners, transforming travel from search-heavy research to one-conversation booking.

## Core Explanation
Travel AI: (1) Inspiration + Discovery -- LLM conversational trip planning. User describes preferences (budget, interests, pace) -> AI generates destination suggestions + itinerary; (2) Search + Booking -- AI aggregates flights, hotels, activities across providers. Conversational booking: "Find me a hotel in Shinjuku under $200 with a gym"; (3) Price prediction -- ML on historical pricing predicts optimal booking window. Hopper: Buy/wait recommendation with price freeze guarantees; (4) In-trip assistance -- AI translation, navigation, local recommendations.

## Detailed Analysis
Expedia (2024): ChatGPT-powered conversational trip planner in app. Natural language flights/hotel search. Booking.com AI Trip Planner (2023-2025): GPT-4 integration for destination discovery and itinerary building. Hopper: ML trained on years of real-time pricing data. Rabbit (discontinued) / Hopper Cloud: B2B API for fintech/travel companies. Price Freeze: lock price for small fee. Cancel for Any Reason: AI-calculated premiums. Google Travel: Gemini integration (2025). Features: trip summarization (aggregate reservations from Gmail), Generative AI itinerary suggestions. Key challenge: dynamic inventory -- flights change prices every few minutes. ML models must predict at this granularity.