8. Two people, A and B, play a game: they toss a coin several times in a row. The game ends when the cumulative number of times the head (or tail) side is up reaches 5. When the game ends, if the cumulative number of times the head side is up reaches 5, A wins; otherwise, B wins. What is the probability that the game is decided in fewer than 9 tosses? $\qquad$ .
8. $\frac{93}{128}$.

Consider the scenario where the game ends after 9 tosses. In this case, the first 8 tosses result in 4 heads and 4 tails, with a probability of $\frac{\mathrm{C}_{8}^{4}}{2^{8}}=\frac{35}{128}$. Therefore, the probability that the game ends in fewer than 9 tosses is $1-\frac{35}{128}=\frac{93}{128}$.