Flex Order Entry (C1 Only)
Orders for FLEX options may be entered using the New Order Single, New Order Multileg, New Order Cross, or New Order Cross Multileg message types. The OSI symbol specified in Symbol (55) will determine the type of FLEX product being traded.
Existing FLEX symbols can be traded during GTH sessions but currently new symbol creation is not permitted during GTH sessions. Effective July 13, 2026 FLEX symbol creation will be allowed for GTH-Eligible proprietary index and GTH-Eligible multilist options starting at 7:30 a.m. ET. FLEX symbol creation in GTH prior to 7:30 a.m. ET will continue to not be permitted. Additionally, during GTH or Curb sessions, trading of percentage FLEX or FLEX DAC orders will not be permitted. FLEX symbol creation is enabled during the Curb trading session.
| Underlying Security | Lead Char | Settlement Type | Exercise Style |
|---|---|---|---|
| Index | 1 | AM | American |
| Index | 2 | AM | European |
| Index | 3 | PM | American |
| Index | 4 | PM | European |
| Index | 5 | Asian | European |
| Index | 6 | Cliquet | European |
| Equity/ETF | 1 | PM | American |
| Equity/ETF | 2 | PM | European |
For example, an OSI of 3SPX would be used to enter a FLEX order or cross for an SPX option that is PM settled and that has an American exercise style.
Asian settlement types further encode in the fifth character an observation day of month for index value observations.
| Lead Char | Symbol Abbr. | Observation Day of Month |
|---|---|---|
| 5 |
|
|
For example, OSI 5RUTC reads as "Asian RUT option having capped observation day of month 13."
Cliquet settlement types encode the underlying index in the second character, a cap return percentage in the third and fourth characters, an observation in the fifth character, and a creation day of month in the sixth.
| Lead Char | Symbol Abbr. | Cap % (whole) | Cap % (frac) | Obs. Day | Creation Day |
|---|---|---|---|---|---|
| 6 |
|
|
|
|
|
For example, OSI 6DCH8T reads as "Cliquet DJX option having capped return percentage of 2.35%, observation day of month 8 and creation day of month of 30."
| Type | SPX | RUT | DJX |
|---|---|---|---|
| AM Amer | 1SPX9 | 1RUT9 | 1DJX9 |
| AM Euro | 2SPX9 | 2RUT9 | 2DJX9 |
| PM Amer | 3SPX9 | 3RUT9 | 3DJX9 |
| PM Euro | 4SPX9 | 4RUT9 | 4DJX9 |
If tag Symbol (55) is as FLEX OSI symbol, then expiration date, strike price, and call/put indicator are also required.
Alternatively, the Cboe Identifier for an existing FLEX symbol can be specified in Symbol (55).
FLEX can be traded as a percentage of the closing price of the underlying for the day by indicating PriceType (423) = 1. Price (44) and LegPrice (566) must be in percentage terms if and only if the strike price of the FLEX option is also in percentage terms. When a percentage Cboe symbol is specified for Symbol (55), but no PriceType (423) value is provided, the order will be rejected. FIX users may opt-in to receive restatement messages at the end of the day once the percentage price has been converted into dollars. Complex FLEX orders containing at least one option leg which is not a FLEX option may not be submitted using percentage terms.
FLEX orders initiating an auction are required to specify FLEXAuctionDuration (21010). The minimum valid value for FLEXAuctionDuration is 3,000 milliseconds. The maximum valid value is 300,000 milliseconds.
FLEX orders require Price (44) be provided. All complex FLEX orders must specify LegPrice (566) per leg, unless routed directly to the floor. When specifying FloorRoutingInst (22303) = D to route complex FLEX orders directly to the floor, leg prices are optional and can be provided for all legs, a subset of legs, or left blank. LegPrice (566) must be left blank for any Option Leg of a Complex FLEX Order that is not a FLEX Option. Complex FLEX orders responding to an auction should not specify any LegPrice (566).