No. Well. Mostly No.
Grid is much newer than Flexbox and has a bit less browser support. That's why it makes perfect sense if people are wondering if CSS grid is here to replace Flexbox.
To put a point on it:
- Grid can do things Flexbox can't do.
- Flexbox can do things Grid can't do.
- They can work together: a grid item can be a flexbox container. A flex item can be a grid container.