It's a continuous change.

Block reward gets lower over time through halvenings, and transaction fees grow over time.

Recently, on block 788695 the transaction fees(6.701 BTC) were higher than the current block reward(6.25 BTC).

This has happened before though, for example in 2011 at block 157077 the transaction fees were 85.974 BTC, which was more than the 50 BTC reward at the time.

We'll see this happening more often in the future.