Skip to main content
Before placing an order, start with two things:
  1. pick the series you want to trade
  2. decide whether you want principal + yield exposure through ST or rewards-side exposure through EPT
The same vToken can have multiple series open at different maturity dates, and each series has its own ST/vToken and EPT/vToken orderbooks (though economically they are the same underlying book, as explained below).

​
What the Orderbook Is

ArcX runs an APR-priced orderbook for two series-specific tokens:
  • ST trades against vToken
  • EPT trades against vToken
You are not placing orders in raw dollar price. You are placing orders in APR. That matters because ST and EPT are both time-dependent claims. As maturity gets closer, the token amounts implied by the same economic deal change. APR is the stable way to express the deal you want.

​
Why APR Is the Quote Unit

If the book were quoted directly in ST price or EPT price, every order would appear to drift mechanically as time passed. For example, imagine you want the same annualized ST deal for a series with 60 days left and then again with 10 days left.
  • with 60 days left, that APR implies a larger ST amount per vToken
  • with 10 days left, that same APR implies a smaller ST amount per vToken
If orders were quoted directly in token price, the same economic intention would have to be constantly repriced as maturity approached. APR avoids that problem. When you place an APR-based order, you are saying:
  • what annualized return you want on the ST side, or
  • what annualized deal you are willing to accept on the EPT side
The token amounts shown in the book can still drift with time, but the APR keeps the economic intent stable.

​
How to Think About APR by Side

When placing a limit order, the cleanest way to think about APR is:
Order typeWhat your APR means
Buy STThe minimum APR you want in exchange for locking your vTokens into the principal + yield side
Sell STYou are selling ST at a discount, so the APR is the maximum discount / worst yield deal you are willing to accept
Buy EPTYou are paying upfront for rewards-side exposure, so the APR is the maximum APR you are willing to give the other side
Sell EPTYou are selling the rewards side, so the APR is the minimum APR the buyer must pay to get equivalent EPT exposure
In plain English:
SideBetter for you
Buy STHigher APR
Sell STLower APR
Buy EPTLower APR
Sell EPTHigher APR
That is the main directional rule to keep in mind when reading the book.

​
How to Reason About Price

The book is quoted in APR, but users still need a simple way to think about token price:
  • ST trades below 1 vToken
  • EPT trades based on the market’s view of future CreditToken generation and reward distribution, and as an EPT buyer you want the price to leave room for your expected return
As maturity gets closer, the same APR implies different ST and EPT amounts. That means:
  • a resting order can display different token size later even if the order itself has not changed
  • the same APR at different times does not imply the same absolute return
  • percentage return stays comparable, but the remaining notional opportunity shrinks as maturity approaches

​
Market Orders vs Limit Orders

​
Use a market order when:

  • you want immediate execution
  • enough compatible liquidity is already resting in the book
  • the current effective APR is acceptable for your full size
  • you are comfortable setting slippage tolerance in the UI

​
Use a limit order when:

  • liquidity is thin or taking available depth would move your APR too much
  • you care about a specific APR more than immediate execution

​
How Matching Is Checked

ArcX uses an off-chain matching service to find candidate matches between compatible orders. The service proposes fills, but final settlement is checked by on-chain logic. The contracts verify that each fill stays within:
  • the APR bounds the user selected
  • the slippage bounds the user selected
  • the settlement constraints for the relevant ST, EPT, and vToken transfers
The matcher cannot force a user into a worse APR or an invalid fill outside those on-chain constraints.

​
ST and EPT Are the Same Orderbook!

Although ST and EPT may look like two different books in the UI, the reality is that they are the same underlying orderbook. The same underlying vToken value can be split into: 1 vToken=1 ST+1 EPT1 \text{ vToken} = 1 \text{ ST} + 1 \text{ EPT} That means pricing either ST or EPT in vTokens automatically decides the price of the other side. Or in other words:
  • 1 vToken can always be split into 1 ST + 1 EPT
  • 1 ST + 1 EPT can always be combined back into 1 vToken
An order on one side also implies an economically equivalent order on the other side:
  • a Buy ST is also a Sell EPT
  • a Buy EPT is also a Sell ST
For example, a Buy ST can match directly with a Sell ST. But it can also be satisfied by splitting vToken into ST + EPT and selling the EPT side. The same logic works in reverse on the EPT side too. See Orderbook Mechanics for the full matching logic.

​
Some More Things to Know About the Orderbook

  • Limit orders can be partially filled
  • Cancelling an order only unlocks the unmatched remainder
  • Market orders let you set slippage tolerance in the UI so the final result does not drift too far from the quoted APR
  • You cannot match against your own resting orders

​
Next Steps