Core concepts
The handful of terms you need to use Spield confidently — PT, YT, maturity, par, fixed vs implied APY — explained in plain language.
You only need a few terms to use Spield confidently. Here they are, in plain language. For a full alphabetical list, see the Glossary.
The two tokens
PT — Principal Token
A PT is a fixed-rate bond. Each PT redeems for exactly 1 USDC at maturity. You buy it today for a little less than 1 USDC, and the gap is your guaranteed return.
Example: if 1 PT costs 0.97 USDC today and matures in 90 days, holding it to maturity returns ~3.1% over those 90 days — locked in the moment you buy.
YT — Yield Token
A YT is a claim on all the yield the underlying position earns until maturity. It's cheap, so a small amount of USDC buys exposure to the yield on a much larger position — that's the "leverage." If realized yield beats expectations, YT wins; if it underperforms, YT can decay toward zero.
The invariant that ties them together
At every moment, Value(position) = Value(PT) + Value(YT). The protocol never creates or destroys value when it splits a position — it only separates it.
Time and price
The pieces of the protocol
| Concept | What it is |
|---|---|
| Yield source | Where the real yield comes from — Stellar's Blend lending market. Your USDC earns borrower-paid interest there. |
| Fixed-Rate Vault | The simplest product: deposit USDC, get a receipt for a guaranteed payout at maturity. You never touch PT/YT directly. |
| Market | The trading venue (a time-decay AMM) where PT is bought and sold, and where YT is routed. |
| Liquidity | PT + USDC supplied to the market to earn swap fees. |
| Solvency | Live, on-chain proof that the protocol's backing covers everything it owes. |
How they fit together
Once these click, the rest of the docs is just detail. Next: Key benefits or the deeper How It Works.