It's not a huge issue, but it's worth minimizing your exposure/risk, so to speak. In other words, I would just keep your options open and continue to entertain other offers. 6 months is a very long time in Silicon Valley. All kinds of things can happen (the person who offered you the job gets fired, there is a restructuring, the company undergoes a merger/acquisition, it downsizes, it pivots in a different direction and no longer needs you, or it scales up and ends up needing to fill the role faster with somebody else, etc etc).

By their nature, tech companies know what they need today, predicting what they need in 6 months doesn't always go well.