What's the relation between /base and /optimism ?

Optimism and Base are L2s, they compete for TVL and still they have a certain relationship. 

What is that exactly?
Base is built on Optimism’s open-source OP Stack. 

Now what is OP Stack? 
OP Stack is a modular, open-source framework for building blockchains created by the Optimism team.

Base is the second Core Dev team working on the OP Stack contributing to the development and contributing a portion of sequencer revenue with OP.

Base grows, OP grows!

img credits: base dot org

Marketer | Terminally Onchain | Hosting /degenverse /basedacademy | Player /fbi

And both of their transaction fees help fund Retro Funding :)