To my understanding, we now started something called ice age period where difficulty bomb becomes harder exponentially and this was implemented to make sure everyone switches to new PoS chain when it is out.

However according to recent articles PoS will start off in hybrid mode where 99 blocks are still validated via PoW and 1 is validated via PoS (again we can never be 100% sure this is the case, but it looks like it from what I've read). This means we will still be able to mine for a couple of months until PoS is fully implemented.

My question is: the hybrid stage of PoS requires hard fork, will this hard fork remove difficulty bomb and will another difficulty bomb be implemented to account for next step of PoS transition, or will it be possible without hard forking again?

Subsequently, it seems like Casper is still in development, what happens if it is not ready in time before difficulty bombs effect becomes too hard?

1 Answer 1


The effect of the difficulty bomb reveals itself slowly at first and becomes exponentially more obvious over time (as you indicate). Without a hard fork, the network will grind to a halt, which (as you also indicate) forces everyone to move to the upgraded code. Its effect is just starting to become noticable: https://etherscan.io/chart/blocktime.

The pending release of Metropolis contains many fixes/upgrades (detailed in the EIP repo) and lays the groundwork for the switch to POS, but it does not yet implement POS. It is my understanding that Casper, which is also not ready, is either required or at least highly desirable to implement POS.

Of course, it's impossible to predict the future, but I would guess that part of the Metropolis release will reset the difficulty bomb to a later date that will extend far enough into the future to allow for Casper and POS to be properly prepared and tested.

Summary: Difficulty bomb is already exploding (slowly), and will be reset with the Metropolis hard fork which does not include POS or Casper.

  • Thank you for the answer, clarifies the roadmap a lot to me :) does metropolis have an eta release time by any chance?
    – Ilja
    Commented Jun 5, 2017 at 5:36
  • I've heard late summer, but nothing definitive. The recent rise in the price of ether has attracted more mining hash power, which has somewhat mitigated the effect of the difficulty bomb giving them slightly more time the way I understand it. Commented Jun 5, 2017 at 8:09

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