There is a particular kind of quiet that follows a pull request closed without merging. No outage, no fork, no emergency upgrade — just a draft returned to the workshop after review. On September 25, that quiet settled over SIMD-0649, a Solana improvement proposal designed to bind transaction ordering to a fee-priority rule. It never reached mainnet. For most of the market, this is a non-event. Nothing broke. Nobody lost funds. The validator set produced blocks exactly as before.
And yet, for anyone who has spent years peering through the haze of speculative value that surrounds "fair ordering" narratives, the closure matters. It tells us where Solana's MEV problem actually lives, and how narrow a fix can be before it becomes decorative. It also arrives during a bear market in which survival, not upside, is the operative question — and in which every governance decision at the protocol layer is quietly re-evaluated for what it says about long-term structural integrity rather than short-term price.
I have watched this movie before. In 2017, I left traditional finance to audit the liquidity flood of the ICO boom, reading fifteen early-stage whitepapers in a matter of weeks. What I learned then — and what I have re-learned in every cycle since — is that the rules a network chooses about ordering and access determine far more about its long-term value than any single upgrade announcement. SIMD-0649 is one such rule, and its failure is more instructive than its success would have been.
Context: the architecture that made this proposal necessary
To understand why SIMD-0649 was written at all, you have to start with the structural position of the Solana leader. Unlike Ethereum, Solana has no public mempool. Transactions do not wait in a shared pool where builders observe and bid; instead, they are forwarded, often by RPC nodes, directly to the current slot's block producer. That leader — a rotating validator — decides which transactions to include, how to group them, and in what order they settle. This is efficient. It is also, in the language of market microstructure, an enormous concentration of discretion.
Solana's ledger organizes transactions into entry batches, which are further partitioned into forward-error-correction sets and ultimately into shreds — the packetized units that propagate across the network. FEC, or forward error correction, allows a receiver to reconstruct data even when some fragments are lost in transit, which is central to Solana's throughput story. Agave, the primary validator client, and Firedancer, Jump Crypto's high-performance client, both target a batch size on the order of two FEC sets, roughly sixty-four shreds. The leader chooses where batches begin and end. That choice is invisible to the user, but it is the terrain on which transaction ordering is actually decided.
This architecture has a specific consequence for MEV, or maximal extractable value. On Ethereum, the ordering problem was externalized into proposer-builder separation and MEV-Boost, creating a competitive auction with its own pathologies — relay trust, builder centralization — but also a public marketplace where order flow is priced and partially observable. Solana deliberately avoided that route. Its design keeps ordering inside the protocol, which means any fairness rule must also live inside the protocol, and must therefore contend with the leader's discretion directly.
That is the context in which the proposal emerged. And it is why the rules governing batches — seemingly a technical detail — carry outsized weight for anyone trying to understand who actually captures value on Solana.
Core: a patch that audits order but not entry
SIMD-0649 entered this terrain with a modest ambition. Within a single entry batch, it would require that non-exempt transactions appear in non-increasing priority order. Priority, in this design, is a score: the reward the leader receives for including a transaction, divided by that transaction's request cost under a defined pre-execution cost model. The reward includes the priority fee plus the non-burned portion of the base fee. A "one-unit guard" was specified to keep integer calculations consistent across clients, so that Agave and Firedancer would reach identical verdicts on the same block. The rule would be enforced at replay: a validator rebuilding the ledger would compare priorities and could mark a block invalid if the ordering was violated.
That is the whole of it. The proposal did not attempt to decide which transactions enter a block. It did not create a slot-level priority queue. It did not touch transaction selection. It only audited the sequence inside a batch.
The significance of this narrow scope becomes clearer when you look at what remained untouched. Three things stand out.
First, the leader still selects transactions. Nothing in the rule prevents a leader from including or excluding any transaction for any reason. Second, the leader still defines batch boundaries. A batch is not a natural unit; it is a scheduling decision. If a leader wishes to separate two competing transactions, the simplest method is to place them in different batches. Third, the rule says nothing about cross-batch ordering. A high-priority transaction that arrives later — or is deliberately deferred — does not jump ahead of a low-priority transaction in an earlier batch merely because its score is higher. The comparison window ends at the batch edge.
In my own audit work during the 2020 DeFi Summer, I spent weeks dissecting how over-collateralized lending protocols misaligned incentives with user behavior. The lesson I carried forward was consistent, and it applies here directly: a rule is only as strong as the boundary it refuses to cross. SIMD-0649 defined a boundary — the entry batch — and enforced fairness within it. But it left the most consequential lever, the boundary itself, in the hands of the very actor whose discretion was in question.
There is a second, subtler problem. Priority fees are paid back to the leader. The base fee has a burned portion that remains a real cost, but the priority component returns to the block producer's own balance. This means a leader can, in principle, pay itself a priority fee to favor its own transactions, and the ordering test would not object. The proposal's authors were, to their credit, candid about this: the rule is not a guarantee against preferential treatment, MEV, or slippage. It is a mechanism for making one dimension of ordering auditable.
I want to be precise here, because the distinction matters. Auditability is not fairness. A rule that lets you verify a sequence has occurred in a stated order is not the same as a rule that ensures the sequence is desirable. The first is a transparency instrument; the second is a policy. SIMD-0649 was the former.
And there is a third gap, which I find the most revealing because it is empirical rather than architectural. The proposal required a minimum batch size — at least two FEC sets, about sixty-four shreds — to prevent the rule from being defeated by trivially tiny batches. This is a sensible guard. But neither the proposal nor the September 23 review provided measured data on how often leaders currently produce batches smaller than that threshold, nor did they present sensitivity tests across different minimum sizes. A design that changes production behavior without knowing the baseline distribution is a hypothesis, not an engineering specification.
The review itself cut to this point. If a leader finds it advantageous to close a batch precisely because conflicting transactions are separated, the rule cannot stop it. The reviewer asked for current batch-size data segmented by scheduler, client, and market condition, and for sensitivity analysis across minimum thresholds. These are not hostile questions. They are the questions any careful protocol change should answer before it touches the ordering layer.
Contrarian: the loophole moves rather than closes
The conventional reading of the closure is that Solana's fair-ordering effort stalled. I think that is too simple, and it misses the more interesting dynamic. What SIMD-0649 reveals is not that Solana cannot order fairly, but that batch-boundary arbitrage is a more durable problem than intra-batch manipulation.
Consider what a rational MEV searcher does when intra-batch ordering is constrained. The obvious adaptation is to stop competing within a batch and start competing across them. If two transactions cannot be placed in a way that violates non-increasing priority inside one batch, the searcher places them in adjacent batches where the test never runs. The loophole does not disappear; it relocates. And because the leader controls batch boundaries, a searcher who can coordinate with or predict leader behavior gains the same edge that intra-batch ordering used to provide.
This is the paradox of decentralized trust that keeps surfacing in Solana's design. The system is decentralized in its validator set, its client diversity, and its consensus. It is not decentralized in its ordering discretion, which remains concentrated in the slot leader. A rule that audits ordering inside a batch is a meaningful step only if competitive transactions reliably share a batch. When they do not, the rule is a fence around an empty field.
There is a macro dimension I have been circling for years. In traditional markets, the equivalent problem was solved — or at least managed — through regulated order-handling rules and transparent auction mechanisms. Payment for order flow, colocation, and the exchanges' own matching priorities all sit inside a supervisory perimeter. Crypto has no such perimeter. It has client teams, improvement proposals, and the informal authority of whoever maintains the dominant implementation. The fact that Agave and Firedancer's implementation willingness functions as a de facto veto is not a design flaw; it is the actual governance. Anyone who watched the 2022 collapse of Terra-Luna and FTX knows that informal governance is where the real risk hides.
And here the timing deserves scrutiny. The PR was closed after a review and after calls for more discussion and client-developer support. That sequence is healthy — the SIMD process filtered out an under-specified rule. But it also means the fate of ordering fairness now rests on whether Firedancer, whose performance targets are built around low latency, is willing to absorb additional replay checks and a minimum-batch-size constraint. In August discussions, latency concerns had already been raised about replaying partially received data. Waiting for two full FEC sets before validating order could, in low-throughput conditions, add broadcast delay. None of these risks were measured; they were noted.
I do not think the closure is a defeat. I think it is the system correctly refusing to ship a rule whose benefits are conditional and whose costs are unquantified. The vacuum behind the hype is not that Solana failed — it is that "fair ordering" was never a single switch, and the market treated it as one. Compare that to the NFT mania of 2021, where a cultural narrative raced far ahead of any economic sustainability. The pattern repeats: a compelling story, a structural gap, and a market that prefers the story.
Takeaway: what the next revision has to prove
If SIMD-0649 returns, it will have to do three things it did not do this time. It must either constrain batch-boundary discretion or introduce a cross-batch comparison that makes boundary arbitrage unprofitable. It must publish measured batch-size distributions across clients and market conditions. And it must state plainly, in its own text, that it does not prevent leader self-dealing through self-paid priority fees.
Until then, the honest position is that Solana's ordering layer remains a work in progress, and the September 25 closure is a data point in a longer negotiation rather than a verdict. The deeper question — the one that will outlast this specific proposal — is whether any intra-protocol rule can meaningfully constrain an actor whose power is defined by the boundaries it draws.
I will be watching three signals over the next one to two SIMD cycles: whether Firedancer and Agave publicly converge on a minimum batch size, whether measured batch distributions are published at all, and whether any subsequent draft touches the boundary itself rather than the space inside it. Those three signals will tell us more than any headline about Solana's MEV governance.
Listen to the silence between these data points. The next proposal will tell us whether Solana intends to redraw the boundary, or merely decorate it.
