Bitcoin’s blockchain is being used less like a payment rail and more like a bulletin board. OP_RETURN outputs, the mechanism that lets users embed arbitrary data into Bitcoin transactions, are climbing toward 700,000 and approaching all-time highs.
The surge is largely driven by protocols like Runes, which piggyback on OP_RETURN to inscribe token data directly onto Bitcoin’s base layer.
What’s behind the spike
Two forces are colliding to produce this wave of activity.
First, Bitcoin Core v30, released on October 10, 2025, dramatically loosened the rules. The update raised the default relay policy limit on OP_RETURN data from 83 bytes to roughly 100 kilobytes, a more than 1,000x increase. It also allowed multiple OP_RETURN outputs within a single transaction, where previously only one was permitted.
Second, the Runes protocol has become the dominant consumer of that newly expanded capacity. A significant portion of recent OP_RETURN traffic traces back to Runes-related activity, with users minting and transferring fungible tokens that exist as data payloads on Bitcoin rather than on a separate chain.
The combination has pushed daily Bitcoin transaction counts above 800,000 at peak moments, the highest levels recorded since late 2024. According to CryptoQuant data from June 2026, approximately 80% of that volume consists of micro-transactions worth less than 0.01 BTC.
Congestion without the price tag
Mempool congestion peaked at roughly 128,000 pending transactions in June 2026, the highest backlog since February 2025. Yet median transaction fees have remained subdued. The reason is straightforward: these OP_RETURN-heavy transactions tend to be small and low-priority. They fill up blockspace without competing aggressively on fee rates, because the users sending them aren’t in a rush to settle large economic transfers.
Some mining pools have responded by prioritizing larger OP_RETURN batches, essentially sorting their own transaction queues to maximize the yield from this new class of data-embedding activity.
The blockspace debate heats up
BIP-110, a proposal currently under discussion, represents one attempt to formalize rules around blockspace allocation and transaction prioritization. The proposal reflects a broader philosophical split within the Bitcoin community: should the network optimize for monetary transfers, or should it accommodate the growing demand for data storage?
It’s worth noting that despite the relaxed limits introduced in Bitcoin Core v30, larger nonstandard payloads haven’t meaningfully increased since the update. Most transactions still use standard formats associated with Runes. The 100 kB ceiling exists, but few are bumping against it.