# 4 MB transaction relay

Research: relaying transactions up to 4 MB, the whole block weight. Stock Bitcoin Core stops at 100 kvB, so it needs a patched node; none relays them here today.

URL: https://blockspace.wiki/research/4mb-transaction-relay/

**Status on [blockspacelabs.com](https://blockspacelabs.com): Research**, the first card in the Research group.

## What it is

The Labs site describes it as "relaying transactions up to 4 MB, the whole block weight". A block may weigh up to 4,000,000 [weight units](https://blockspace.wiki/glossary/weight-unit/). Relay policy is stricter: "Stock Bitcoin Core treats a transaction over 400,000 weight units (100 kvB) as non-standard and does not relay it, so this needs a patched node." A transaction above that size is not a [standard transaction](https://blockspace.wiki/glossary/standard-transaction/), so ordinary nodes will not pass it on, even though a block may contain it.

## Where it stands

It is a research project, not a running service. The Labs node runs stock Bitcoin Core (/Satoshi:28.2.0/, as of block 972,320, 2026-10-20 12:17:53 UTC), which keeps the 400,000 WU limit. The card says it plainly: "No node here relays 4 MB transactions today." It stays marked Research until such a node runs.

## Background

block.space's data-types reference names the limit `MAX_STANDARD_TX_WEIGHT`. It says a larger transaction, such as the 3.94 MB Taproot Wizards inscription it cites, needs direct-to-miner submission. The [relay policy](/concepts/relay-policy/) page sets this limit beside the node's other policy settings, and [weight units and vbytes](/concepts/weight-units-and-vbytes/) explains how a transaction is weighed.

## Related research

The standard transaction size is one of the relay levers in [blockspace expansion policy](/research/blockspace-expansion-policy/). The [policy observatory](/research/policy-observatory/) proposes to count mined transactions over 100 kvB, which reach miners off the standard relay path.

Sources:

- The blockspacelabs.com page (index.html) · https://blockspacelabs.com
- Blockspace Holdings records
- block.space docs: data types · https://block.space/docs/datatypes

Live figures: relay as of block 972,320, 2026-10-20 12:17:53 UTC

Updated: 2026-10-20