S-Token (Shield & Surplus)

"Shield + Surplus Yield = Smart Alpha"

S-Token is the "High Yield" engine of AquaFlux. It is designed for users who want to earn significantly more than the standard rate and are comfortable taking on the role of a Risk Underwriter.

What it is S-Token

S-Token is the Shield, first-loss buffer that protects P and C. In return, it can earn a Surplus yield: a slice of coupons, a share of protocol fees, and a possible points or airdrop reward from issuer.

The Core Concept: You are the Insurer

The best way to understand S-Token is through an insurance analogy:

• P-Token Holders are the Insured. They accept a lower return in exchange for safety.

• S-Token Holders are the Insurers. You provide that safety (First-Loss protection).

Why do it? Because insurers get paid Premiums. In AquaFlux, these "premiums" come in two powerful forms:

1. Intrinsic Yield (S-Token): The base asset's yield + fees.

2. Extrinsic Rewards (SS, Staked S-Token): The protocol's incentive rewards + upside.

S-Token (Shield, The Underwriter)

By holding S-Token, you are the Underwriter of the pool. This position gives you two powerful rights:

1. The Yield: You earn a share of the underlying asset's principal and coupon. It's the intrinsic cash flow from the asset itself.

2. The Exclusive Ticket: S-Token is the only way to access SS (Surplus). Think of S-Token as your membership pass—without it, you cannot participate in the underlying's future upside.

The Risk (First-Loss)

Just like an insurance company, if valid claims are made (i.e., the asset defaults or loses value), you pay first. Your capital absorbs the loss to protect P-Token holders.

SS (Staked S, The Bonus)

This is the "Hidden Gem" of the system. While S-Token captures the asset's yield, SS (Surplus) captures the protocol's upside.

Crucial Rule:

1. Stake S-Token: Stake your S-Tokens into the protocol.

   • Note: Once staked, your S-Tokens are locked until the asset matures. You cannot unstake early.

2. Earn SS Linearly: SS is generated continuously based on your staked amount. The more you stake and the longer you wait, the more SS you earn.

3. Claim & Trade Anytime: While your S-Token is staked, your earned SS is liquid. You can claim your SS rewards at any time and sell them on the secondary market if you wish.

Think of it this way:

• Staking S = Planting a tree. You can't move the tree until harvest season (Maturity).

• Receiving SS = Gathering fruit. You can pick and sell the fruit (SS) whenever you want, while the tree continues to grow.

---

---

How it works

• Loss waterfall

  • S-Token absorbs losses first (up to its coverage).

  • If losses exceed S, C-Token is reduced next.

  • Only extreme residual loss may reach P-Token.

• Cash flows to S

  • Coupon share: A fixed % of each coupon payment.

  • Protocol fees: A defined % of AquaFlux fees (swap/wrap/split/merge/LP fees, etc.—see dApp).

  • Issuer incentives: A possible points or airdrop reward from issuer.

• Pricing (no hard par): S’s fair value ≈ (expected coupon share + expected fees + expected residual) − (expected losses). Expectations change with asset quality, coverage ratio, time to maturity, and market sentiment.

Who it’s for

• Yield hunters / risk takers who understand first-loss dynamics.

• Structured-yield strategies selling downside in exchange for higher carry.

Acquire & Exit

• Acquire

  • Wrap a supported RWA and Split into P/C/S.

  • Buy S-Token directly in the pool/AMM.

• Exit

  • Sell anytime at market price (T+0).

  • At maturity: if the bond repays in full, any unused S buffer + final fee/coupon shares are distributed to S holders. If losses occurred, your S position may be partially/fully reduced.

S Tranche Valuation

Definition The S-Token is the junior, first-loss tranche. Its present value (PV) is the sum of upside components minus expected loss:

$$\mathrm{PV}_{S}=\mathrm{PV}_{\text {coupon share }}+\mathrm{PV}_{\text {fee share }}+\mathrm{PV}_{\text {points/airdrop }}-\mathrm{PV}_{\text {expected loss }}$$

---

Now, let's decompose each term in the formula, let's define

• Face value per unit: N (e.g., N=100).

• Time to maturity: T (years).

• Discount rate: r (annual; discount via (1+r)).

• Bond coupon rate: c (annual).

• Coupon share to S: γ (e.g., 20% of total coupon).

• Pool fee rate per swap: f (e.g., 0.20%).

• Annual turnover (volume/TVL): v (turnover per year).

• Protocol fee split to S: α (e.g., 50%).

1. Coupon Share

If coupon is realized at maturity:

$$\text{PV}_{\text{coupon share}} = \frac{\gamma c N}{(1 + r)^T}$$

1. Fee Share

You can check the exact fee accumulation in the on-chain vault. And you can also use the following methods to make an estimate.

Currently this mainly considering AMM fees, and we will add split/merge, wrap/unwarp fees later.

Annual fees attributable to notional N:

$$Feeyear=f⋅v⋅N$$

S receives fraction:

$$\text{PV}_{\text{fee share}} \approx \frac{\alpha f v N}{(1 + r)^{T}}$$

1. Points / Airdrop

You need to calculate according to the specific airdrop rules.

• Check the rule: emission pace, eligible actions (LP, stake, quests), and any boosts.

• Time matters: count only active days you expect to participate.

• Apply a haircut: reflect eligibility risk, snapshot timing, vesting/lockups, and token-price uncertainty.

1. Expected Loss

You can use different risk models to calculate.

S is the first-loss tranche. Keep it simple with a blended annual loss assumption:

• Use bands, not a single number: Conservative / Base / Optimistic.

• What drives it: issuer quality, asset health, S coverage (thicker S = more buffer), diversification, and historical behavior.

• Cap awareness: S’s annual loss cannot exceed its coverage size; excess loss would waterfall to senior tranches.

• Update cadence: revisit after material events (audits, covenant breaches, ratings watch, liquidity stress).

• Presentation: show the three bands alongside key context (coverage %, asset type, tenor) and note that it’s a prudential estimate.

FAQ

• Is S-Token principal-protected? No. It’s first-loss by design. You are compensated via coupon share, fee share, and potential residual—not by a 1:1 redemption promise.

• Does buying S-Token give me insurance on the asset? No. Buying S-Token is like selling insurance—you act as the first-loss provider (the underwriter). You earn coupon/fee shares and potential residuals for taking that risk, and you’re hit first if losses occur. If you want to buy protection instead, do the opposite: short the S-Token or avoid S and hold P (or P + C) so the first-loss buffer works in your favor.

• When do I earn? Throughout the term (coupon/fee distributions) and potentially at maturity (unused buffer), provided performance is on track.

• What happens if there’s a default? S is reduced first. If the loss exceeds S, it then hits C, and only then P.

• Can S-Token go to zero? Yes, in severe loss scenarios. Size positions accordingly.

• Why do S-Tokens price so differently? Coverage %, asset quality, expected recoveries, time to maturity, and market liquidity all drive expected carry vs. expected loss.