1. A method for execution probability based server-to-client transmission of game code, comprising: operating a computer to receive a current game state of a game being executed on a client computer system from a subset of game code; determining respective probabilities for advancement from the current game state to a set of possible later game states; prioritizing game code required for the set of possible later game states into a prioritized order in accordance with the determined probabilities for advancement from the current game state to each of the set of possible later game states; transmitting game code required for the set of possible later game states in the prioritized order from a server computer system to the client computer system; (a) determining that game code required for a possible later game state of higher priority will not be transmitted from the server computer system to the client computer system in time for its execution on the client computer system without interruption of the game being executed on the client computer system; and (b) upon the determination in (a), transmitting a streaming video of the game from the server computer system to the client computer system, the streaming video of the game corresponding to execution of the game on the server computer system at the current game state in accordance with game input signals received at the server computer system from the client computer system, the streaming video of the game displayed at the client computer system in lieu of a video of the game generated at the client computer system through execution of the game on the client computer system.