We throw around the 21 million cap constantly but barely anyone talks about what actually happens past 2140. Block subsidy goes to zero, no new coins, miners only eat what users pay in fees. Satoshi built it that way on purpose, fine. But is it actually gonna hold up in practice? Like will fee revenue ever be enough to keep a strong global hashrate going and protect the network from attacks? Once that last sat is mined, security is entirely on users competing for block space. Not sure enough people take this seriously.
This gets asked here pretty often tbh, worth using the search before posting. Anyway yeah it's a real concern in theory but ngl none of us are gonna be alive to see the final bitcoin get mined, so in that sense it's kinda like worrying about quantum computing cracking everything... like sure, maybe, but let's cross that bridge when we get there. What I will say is we'll have a much clearer picture within the next 20 years. By around the 10th halving the per-block reward will be tiny and we'll start seeing whether fee income can realistically pick up the slack.
Mining is already getting squeezed margins-wise, let's be real. My honest take? we'll find out when we get there. If I had to guess I'd say we see fewer active miners over time as rewards shrink. Fees will still be a thing but this problem is still way further out than people act like it is. The closer you think you are to that cliff the farther it actually turns out to be.
Right, which is exactly why I don't lose sleep over it. Would anyone 114 years ago have even imagined bitcoin existing? No shot. We have zero idea what the world looks like before then. Humans just can't stop worrying lol. Though I will say the fee sufficiency question starts mattering way sooner than 2140, probably within the next 25 years or so.
Bitcoin has only been around roughly 17 years and look how much ground it's covered, how many forks, how many adaptations. If fees alone can't sustain it by then, something will change. The protocol has shifted before. Satoshi clearly thought about the endgame. My personal bet is it survives on fees, but that depends on a lot of things including whether some other chain has eaten its lunch by then. Just living in the moment and ignoring the future entirely isn't smart either though.
The mining profitability side kind of takes care of itself actually. Unprofitable miners drop off, difficulty adjusts, remaining miners get a bigger slice. That part is self-correcting. The harder question is whether total fee revenue will be enough to make a 51% attack genuinely expensive to pull off. And honestly? nobody has a solid answer to that afaik. We'll get a much better read on it in maybe a decade when subsidy shrinks to the point where fees start exceeding it.
17 years in and we're talking about something 114 years out. If we just extrapolate demand and price trends it seems like fees could scale up massively. The same nominal fee we pay today could be worth multiples more in purchasing power down the line. And if demand keeps growing there's less reason to fear miner exodus or 51% risk. Tech will also keep evolving, mining hardware efficiency included. Still a lot of runway before this becomes an actual crisis.
Ok so 2140 is honestly kind of a misleading date to anchor this discussion to. Even with low fees a full block already brings in something like 0.02 BTC in fees. The block subsidy actually dips below that level around 2056, which is only about 30 years away, not 114. Most people reading this will be alive for that. And by 2076 the subsidy is basically a rounding error compared to fee income. So if security is gonna be a problem it shows up way earlier than 2140. A higher BTC price doesn't automatically fix it either because the value of a successful attack scales up too.
The first half of what the guy above said is spot on and I'm glad someone finally corrected the 2140 nonsense people keep repeating. If this becomes a real issue we'll see signs of it decades earlier, not at the last satoshi. The 4-year halving cycle exists precisely to make any degradation gradual, giving time for ideas to surface and get implemented. So stop quoting 2140 like it's some sudden cliff. The second part though I'd push back on, how bad it gets is still speculative. Could be fine, could not be.
People can't really answer this because we genuinely don't know how miners will behave when fees are their only income. It all comes down to transaction volume. High enough volume, miners stay profitable, network stays secure. The 51% attack scenario only gets scary if miners start leaving in large numbers and hashrate craters. As long as mining stays profitable the only realistic 51% threat is a state-level actor with basically unlimited budget, not some random opportunist.
Actually you don't even need to speculate on this, there's a live comparison sitting right in front of us. BCH block rewards from subsidy plus fees are currently roughly in the same ballpark as what Bitcoin earns from fees alone per block. BCH folks claimed they were building the future of Bitcoin... I don't think this is what they had in mind but here we are. Make of that what you will.
There's a related thread on here that goes deeper on the question of what level of security is actually sufficient, worth digging up if you're interested in that angle specifically.
Satoshi actually said something around 2010 suggesting 20 years, pointing toward 2030 as a checkpoint. If you map out the halvings and what price per coin you'd need for fees to compensate the shrinking subsidy it gets pretty steep pretty fast. By 2036 you'd need fees to cover roughly 0.39 BTC per block, which means either price is very high or fees are chunky. By 2040 you're looking at needing the price to be in the millions per coin just to hold security constant. Some miners will probably quit before it gets that bad which changes the whole picture.
Appreciate the breakdown. Yeah Satoshi's real test date was closer to 2030, not 2140, that's the point most people miss. A few more halvings and we'll have real data. If by 2036 fees can't replace what a 0.39 BTC subsidy was worth, we'll see hashrate start bleeding out well before 2140. Price either has to follow or fees have to hurt users more. One or the other. Still wrapping my head around the 51% angle, specifically how it connects to who actually controls the hashrate infrastructure.
So my point on that is that the realistic 51% risk doesn't come from entities who own their mining rigs outright, those guys have skin in the game and attacking would wreck their own investment. The danger is from someone who can temporarily rent hashpower. There are actual marketplaces for that. If more miners shift toward renting out their rigs rather than using them to mine directly, the attacker's job gets easier because they don't need to own anything permanently. That's the slow-moving threat that doesn't get talked about enough.
Ok that actually clicks now. This is exactly the long-term incentive problem I was poking at in my original post. Subsidy dying doesn't just shrink the security budget in dollar terms, it changes the whole structure of who controls hashpower and why. If by 2140 most hashpower is effectively rented out, then network security is pegged to rental market prices not to Bitcoin's value directly. Gonna be very interesting watching how hashpower liquidity evolves through the next few halvings.
Stop thinking about this as binary, secure vs insecure. Security exists on a spectrum. Even if hashrate drops significantly from today's peak, the network doesn't suddenly become a free-for-all. It just becomes relatively less secure than it is right now, which could still be extremely secure in absolute terms. A lot of people here fall into this trap of narrative thinking where any reduction equals catastrophe. It doesn't. And the fearmongering that comes from that kind of black and white thinking does more harm than good imo.
Ok but what specific countermeasures are you actually talking about? Bitcoin's game theory assumes honest majority hashrate. If that assumption breaks down there's no fallback built into the protocol. So saying 'measures can be taken' without being specific isn't really an answer.
Maybe the reason nobody stresses too hard about this is just that we'll all be long gone before the final block. But here's the thing, if Bitcoin is still running a century from now it means it already survived everything thrown at it. At that point fee sufficiency is almost certainly not the thing that kills it. Satoshi built the transition to be gradual through halvings, not a sudden drop. That gives time to adapt. Either Bitcoin thrives or it fails, but it's not gonna slowly suffocate on fees alone if it's still standing that far out.