Please note that this document temporarily refers to sai instead of dai and skr instead of peth. These are just different variable names and their functionality is identical to what is described in the latest Dai documentation.

sai is a simple single-collateral stablecoin that is dependent on a trusted oracle address and has a kill-switch.

See the developer documentation for a more technical overview.

There are four tokens in the system:

• gem: externally valuable token e.g. ETH
• gov: governance token e.g. MKR
• skr: a claim to locked gems
• sai: the stablecoin, a variable claim on some quantity of gems

Collateral holders deposit their collateral using join and receive skr tokens proportional to their deposit. skr can be redeemed for collateral with exit. You will get more or less gem tokens for each skr depending whether the system made a profit or loss while you were exposed.

The oracle updates the GEM:REF and GOV:REF price feeds. These are the only external real-time input to the system.

skr is used as the direct backing collateral for CDPs. A prospective issuer can open an empty position, lock some skr and then draw some sai. Debt is covered with wipe. Collateral can be reclaimed with free as long as the CDP remains "safe".

If the value of the collateral backing the CDP falls below the liquidation ratio mat, the CDP is vulnerable to liquidation via bite. On liquidation, the CDP skr collateral is sold off to cover the sai debt.

Under-collateralized CDPs can be liquidated with bite. Liquidation is immediate: backing skr is taken to cover the sai debt at the time of bite, plus a liquidation fee (axe); any excess remains in the CDP.

skr seized from bad CDPs can be purchased with bust, in exchange for sai at the s2s price. This sai pays down the bad CDP debt.

Any remaining Sai surplus (joy) can be purchased with boom, in exchange for skr at the s2s price. This skr is burned.

Fees

Stability fee is continuously charged on all open cups according to tax. It makes their debt (tab) increase over time.

Governance fee is continuously charged on all open cups according to fee. It makes their debt (rap) increase over time.

Settlement

sai can be shut down at a given price with cage, after which sai and skr can be exchanged for gems via cash. All outstanding cups are liquidated and the entire pool of gem is tapped to redeem sai at their face value, as if the boom/bust trades were instantly settled at the cage price. Any remaining gems are shared between skr holders.

Practically this means that if the system is undercollateralized on cage, holders of free skr will have their gem share diluted as much as necessary to make sai whole. In other words, skr is a risk bearing token.

Excess collateral contained within a single cup can be reclaimed with bite(cup).

sai glossary (sai help)

Actions:

   bite            initiate liquidation of an undercollateral cup
   boom            buy some amount of sai to process joy (surplus)
   bust            sell some amount of sai to process woe (bad debt)
   cage            lock the system and initiate settlement
   cash            cash in sai balance for gems after cage
   cupi            get the last cup id
   cups            list cups created by you
   draw            issue the specified amount of sai stablecoins
   drip            recalculate the internal debt price
   exit            sell SKR for gems
   free            remove excess SKR collateral from a cup
   give            transfer ownership of a cup
   heal            cancel debt
   help            print help about sai(1) or one of its subcommands
   join            buy SKR for gems
   lock            post additional SKR collateral to a cup
   open            create a new cup (collateralized debt position)
   prod            recalculate the accrued holder fee (par)
   safe            determine if a cup is safe
   setAxe          update the liquidation penalty
   setFee          update the governance fee
   setCap          update the debt ceiling
   setMat          update the liquidation ratio
   setTapGap       update the spread on `boom` and `bust`
   setTax          update the stability fee
   setTubGap       update the spread on `join` and `exit`
   setWay          update the holder fee (interest rate)
   shut            close a cup
   vent            process a caged tub
   wipe            repay some portion of your existing sai debt
   
Vars, Getters, Utils:

   air             get the amount of backing collateral
   axe             get the liquidation penalty
   caged           get time of cage event (= 0 if system is not caged)
   chi             get the internal debt price
   cup             show the cup info
   fee             get the governance fee
   fit             get the gem per skr settlement price
   fix             get the gem per sai settlement price
   fog             get the amount of skr pending liquidation
   gem             get the collateral token
   gov             get the governance token
   cap             get the debt ceiling
   ice             get the good debt
   ink             get the amount of skr collateral locked in a cup
   joy             get the amount of surplus sai
   lad             get the owner of a cup
   mat             get the liquidation ratio
   off             get the cage flag
   out             get the post cage exit flag
   par             get the accrued holder fee (ref per sai)
   per             get the current entry price (gem per skr)
   pie             get the amount of raw collateral
   pep             get the gov price feed
   pip             get the gem price feed
   pit             get the liquidator vault
   rap             get the amount of governance debt in a cup
   ray             parse and display a 27-decimal fixed-point number
   rho             get the time of last drip
   rhi             get the internal debt price (governance included)
   s2s             get the skr per sai rate (for boom and bust)
   sai             get the sai token
   sin             get the sin token
   skr             get the skr token
   tab             get the amount of debt in a cup
   tag             get the reference price (ref per skr)
   tapAsk          get the amount of skr in sai for bust
   tapBid          get the amount of skr in sai for boom
   tapGap          get the spread on `boom` and `bust`
   tau             get the time of last prod
   tax             get the stability fee
   tubAsk          get the amount of skr in gem for join
   tubBid          get the amount of skr in gem for exit
   tubGap          get the spread on `join` and `exit`
   vox             get the target price engine
   wad             parse and display a 18-decimal fixed-point number
   way             get the holder fee (interest rate)
   woe             get the amount of bad debt

Sample interaction using sai

$ export ETH_FROM=0x(...)
$ export SAI_TUB=0x(...)

# Give the system access to our GEM (W-ETH), SKR and SAI balances
# so we can join()/exit() and also draw()/wipe() sai
$ token approve $(sai gem) $(sai tub) $(seth --to-wei 1000000000 ETH)
$ token approve $(sai skr) $(sai tub) $(seth --to-wei 1000000000 ETH)
$ token approve $(sai sai) $(sai tub) $(seth --to-wei 1000000000 ETH)

# If we also plan on using boom() and bust(), a different component
# (called `tap`) will need to have access to our SKR and SAI balances
$ token approve $(sai skr) $(sai tap) $(seth --to-wei 1000000000 ETH)
$ token approve $(sai sai) $(sai tap) $(seth --to-wei 1000000000 ETH)

# We need to have some GEM (W-ETH) balance to start with
$ token balance $(sai gem) $ETH_FROM
2.467935274974511817

# Join the system by exchanging some GEM (W-ETH) to SKR
$ sai join 2.2
Generating 2.200000000000000000 SKR depositing GEM...
$ token balance $(sai gem) $ETH_FROM
0.267935274974511817
$ token balance $(sai skr) $ETH_FROM
2.200000000000000000

# Open a new cup
$ sai open
Opening cup...
Opened cup 62

# We can list our cups at all times
$ sai cups																
Cups created by you...
62

# Lock some SKR collateral in the cup and then draw some SAI from it
$ sai --cup 62 lock 1.5													
Locking 1.500000000000000000 SKR in cup 62...
$ sai --cup 62 draw 89.0												
Drawing 89.000000000000000000 SAI from cup 62...
$ token balance $(sai skr) $ETH_FROM
0.700000000000000000
$ token balance $(sai sai) $ETH_FROM
89.000000000000000000

# We can examine the cup details, `tab` and `ink` representing
# the amount of debt and the amount of collateral respectively
$ sai --cup 62 cup														
cup id 62...
lad: 0x(...)
ink: 1.500000000000000000
tab: 89.000000000000000000
rap: 0.000000000000000000

# We can check whether the cup is still safe
# (ie. whether the value of collateral locked is high enough)
$ sai --cup 62 safe
true

# At some point we will want to wipe our SAI debt
# which means we can also free the SKR collateral
$ sai --cup 62 wipe 59.0												
Wiping 59.000000000000000000 SAI from cup 62...
$ sai --cup 62 free 1.1													
Freeing 1.100000000000000000 SKR from cup 62...
$ token balance $(sai skr) $ETH_FROM
1.800000000000000000
$ token balance $(sai sai) $ETH_FROM
30.000000000000000000

# The `tab` and `ink` values have changed
$ sai --cup 62 cup
cup id 62...
lad: 0x(...)
ink: 0.400000000000000000
tab: 30.000000000000000000
rap: 0.000000000000000000

# We can also `wipe` and `free` outstanding balances of SAI and SKR by calling `shut`
$ sai --cup 62 shut
Closing cup 62...

$ sai --cup 62 cup
cup id 62...
lad: 0x0000000000000000000000000000000000000000
ink: 0.000000000000000000
tab: 0.000000000000000000
rap: 0.000000000000000000

# Exit the system by exchanging SKR back to GEM (W-ETH)
$ sai exit 2.2
Sending 2.200000000000000000 SKR to TUB...
$ token balance $(sai gem) $ETH_FROM
2.467935274974511817
$ token balance $(sai skr) $ETH_FROM
0.000000000000000000

Dai v1 Current deployments

Names for tokens:

• Dai: SAI_SAI
• MKR: SAI_GOV
• WETH: SAI_GEM
• PETH: SAI_SKR

Mainnet:

# sai deployment on ethlive from c2031c0f9f3a186e90b6a3c1905282f7cc58b9f5
# Mon 18 Dec 03:12:57 GMT 2017
# SAI_ADM updated 2019-06-11

export SAI_GEM=0xc02aaa39b223fe8d0a0e5c4f27ead9083c756cc2
export SAI_GOV=0x9f8F72aA9304c8B593d555F12eF6589cC3A579A2
export SAI_PIP=0x729D19f657BD0614b4985Cf1D82531c67569197B
export SAI_PEP=0x99041F808D598B782D5a3e498681C2452A31da08
export SAI_PIT=0x69076e44a9c70a67d5b79d95795aba299083c275
export SAI_ADM=0x9eF05f7F6deB616fd37aC3c959a2dDD25A54E4F5
export SAI_SAI=0x89d24a6b4ccb1b6faa2625fe562bdd9a23260359
export SAI_SIN=0x79f6d0f646706e1261acf0b93dcb864f357d4680
export SAI_SKR=0xf53ad2c6851052a81b42133467480961b2321c09
export SAI_DAD=0x315cbb88168396d12e1a255f9cb935408fe80710
export SAI_MOM=0xf2c5369cffb8ea6284452b0326e326dbfdcb867c
export SAI_VOX=0x9b0f70df76165442ca6092939132bbaea77f2d7a
export SAI_TUB=0x448a5065aebb8e423f0896e6c5d525c040f59af3
export SAI_TAP=0xbda109309f9fafa6dd6a9cb9f1df4085b27ee8ef
export SAI_TOP=0x9b0ccf7c8994e19f39b2b4cf708e0a7df65fa8a3

Kovan:

# sai deployment on kovan from 7d9c16c056c9fc99cdf2f17bc7958837cd17ee41
# Wed Jan  3 16:06:26 -03 2018

export SAI_GEM=0xd0a1e359811322d97991e03f863a0c30c2cf029c
export SAI_GOV=0xaaf64bfcc32d0f15873a02163e7e500671a4ffcd
export SAI_PIP=0xa944bd4b25c9f186a846fd5668941aa3d3b8425f
export SAI_PEP=0x02998f73fabb52282664094b0ff87741a1ce9030
export SAI_PIT=0xbd747742b0f1f9791d3e6b85f8797a0cf4fbf10b
export SAI_ADM=0x74d41fd874234d9bea31ff6b090ba1d0b9dc8785
export SAI_SAI=0xc4375b7de8af5a38a93548eb8453a498222c4ff2
export SAI_SIN=0xdcdca4371befceafa069ca1e2afd8b925b69e57b
export SAI_SKR=0xf4d791139ce033ad35db2b2201435fad668b1b64
export SAI_DAD=0x6a884c7af48e29a20be9ff04bdde112b5596fcee
export SAI_MOM=0x72ee9496b0867dfe5e8b280254da55e51e34d27b
export SAI_VOX=0xbb4339c0ab5b1d9f14bd6e3426444a1e9d86a1d9
export SAI_TUB=0xa71937147b55deb8a530c7229c442fd3f31b7db2
export SAI_TAP=0xc936749d2d0139174ee0271bd28325074fdbc654
export SAI_TOP=0x5f00393547561da3030ebf30e52f5dc0d5d3362c