# How can I track stablecoin supply on-chain? Storage proof or eth_call

Why every on-chain supply figure on ReserveBeat except RLUSD's carries the STORAGE-PROVEN tier and RLUSD's carries QUORUM ETH-CALL: what each tier checks and why RLUSD's supply has no slot to prove.

Every on-chain supply figure on the [coverage board](/) carries a
[source tier](/learn/source-tier), a label for how the number was read. Two
tiers are in use today. Every tracked token except RLUSD reads at the
stronger one, STORAGE-PROVEN. RLUSD reads at QUORUM ETH-CALL. This note explains what
separates them and why RLUSD sits where it does. The tier is about the
reading, not the issuer. Nothing here is a judgment of any issuer's solvency.

## Two ways to read totalSupply()

Supply is read at finalized Ethereum blocks through a quorum of independent
RPC providers, and every provider must return the same bytes. If they
disagree, nothing is published from that read.

**STORAGE-PROVEN.** The token contract's total-supply storage slot is read
with eth_getProof<Cite n={1}/>. The proof is verified locally against the
block's state root, so the value does not rest on any provider's word. A slot
is pinned only after a probe finds exactly one slot equal to totalSupply(),
and that equality is checked again on every snapshot.

**QUORUM ETH-CALL.** The contract's own totalSupply() answer at the same
finalized block, agreed byte for byte across the quorum. There is no proof,
because there is no pinned slot to prove. The figure rests on the providers
agreeing, and the label says so.

## Why RLUSD has no slot to prove

RLUSD keeps its supply in ERC-7201 namespaced storage<Cite n={2}/>, a layout
that places a contract's variables at a hashed location instead of in the
low-numbered slots. ReserveBeat's slot probe checked slots 0 to 200 and found
no slot equal to totalSupply(). With no slot found, none is pinned, and none
is guessed. RLUSD's supply is therefore read at the QUORUM ETH-CALL tier and
labelled that way everywhere it appears. A slot is never invented to lift a
token to the higher tier.

## The tiers today

| Token | On-chain supply tier |
|---|---|
| PYUSD | STORAGE-PROVEN |
| RLUSD | QUORUM ETH-CALL |
| USD1 | STORAGE-PROVEN |
| USDC | STORAGE-PROVEN |
| USDG | STORAGE-PROVEN |
| USDT | STORAGE-PROVEN |
| USDtb | STORAGE-PROVEN |

Each token's page shows the tier beside its supply figure, for example
[RLUSD](/stablecoins/rlusd) and [USDC](/stablecoins/usdc).

## Reading the tier from the API

The keyless API carries the same label, so a program can make the same
distinction a reader does. `GET /v1/board/coverage` returns each token's
`latest_snapshot_tier`, either `STORAGE_PROVEN` or `ETH_CALL`.
`GET /v1/board/tokens/RLUSD` returns the supply series with a `source_tier`
on every point. A client that wants only proven supply can filter on that
field rather than on a list of token names, so it stays correct if a
token's tier ever changes.

## What the tier does not cover

The tier describes the on-chain supply reading only. Reserve figures come
from each issuer's published report and carry their own tier, the issuer's
attestation. A [coverage ratio](/learn/reserve-coverage-ratio) divides only
figures from the same report, so on-chain supply never enters one. The
[methodology](/methodology) and the longer
[methodology walk-through](/research/how-reservebeat-measures-stablecoin-reserves)
cover the rest of the measurement.

## Disclaimer

ReserveBeat renders figures from issuer-published reports and public blockchains, verbatim and at their stated scope. It is not an auditor, makes no attestation, and states no opinion on any issuer's solvency. Nothing here is investment, trading, legal, tax, or accounting advice. No figure published here is a recommendation to hold, buy, sell, or redeem any token.

Tracked tokens are subjects of public data: supply figures are read from their public Ethereum contracts, and composition figures from the issuers' own published attestation reports. No tracked issuer is a customer and none has endorsed this site.

Source: https://reservebeat.com/research/storage-proof-or-eth-call