MarketDataApp · Oct 23, 2026 · Oct 13, 2026 · Oct 14, 2026 · Oct 19, 2026 · Oct 22, 2026
diff --git a/account/plan-limits.md b/account/plan-limits.md
@@ -27,7 +27,7 @@ For users working with options, take care before repeatedly requesting quotes fo
 :::
 
 :::note[Trial plans]
-Starter Trial and Trader Trial do not support `mode=cached`.
+Starter Trial, Trader Trial, and Prime Trial do not support `mode=cached`.
 :::
 
 ## Device Restrictions

diff --git a/api/options/quotes.mdx b/api/options/quotes.mdx
@@ -225,6 +225,30 @@ foreach (var quote in (await client.Options.GetQuoteAsync("AAPL271217C00250000")
 
   The option symbol according to OCC symbology.
 
+- **underlying** `array[string]`
+
+  The ticker symbol of the underlying security.
+
+- **expiration** `array[number]`
+
+  The option's expiration date and time. Equity options expire at 4:00 PM Eastern and index options expire at 4:15 PM Eastern. All timestamps use US Eastern Time (America/New_York). See [Response Timezone](/docs/api/dates-and-times#response-timezone) for details.
+
+- **side** `array[string]`
+
+  The response will be `call` or `put`.
+
+- **strike** `array[number]`
+
+  The exercise price of the option.
+
+- **firstTraded** `array[date]`
+
+  The date the option was first traded.
+
+- **dte** `array[number]`
+
+  The number of days until the option expires.
+
 - **ask** `array[number]`
 
   The ask price.

diff --git a/api/rate-limiting.md b/api/rate-limiting.md
@@ -82,5 +82,5 @@ We provide the following headers in our responses to help you manage the rate li
 - Paying customers can make use of the reduced-price cached mode. Use the `mode=cached` parameter on supported bulk endpoints to retrieve previously cached quotes instead of making a live request. This can save thousands of credits. For more details, refer to the [mode parameter documentation](/api/universal-parameters/mode).
 
 :::note[Trial plans]
-`mode=cached` is not available on Starter Trial and Trader Trial plans.
+`mode=cached` is not available on Starter Trial, Trader Trial, and Prime Trial plans.
 :::
diff --git a/internal/byok-audit-prompt.md b/internal/byok-audit-prompt.md
@@ -65,6 +65,12 @@ reading as a failure.
 
 ## The prompt
 
+{/* TODO(compliance): confirm whether the 4:15:01 PM ET stock cutoff, taken from
+account/data-freshness.md, is also the exchange redistribution-fee boundary for
+stock data. The prompt's "One case that is neither a PASS nor a plain FAIL"
+section treats it as historical, and so as fee-free, until compliance says
+otherwise. See #222. */}
+
 ````
 You are an independent compliance auditor. Audit the repository at [REPO PATH]
 against the Market Data BYOK model and the Market Data data policies. Write your
@@ -183,17 +189,17 @@ or UNRESOLVED.
 | ID | The rule |
 |----|----------|
 | E1 | Every request carries a unique `User-Agent` that names the application and its version. A library default such as `axios/1.6.0`, `python-requests/2.31.0`, or `okhttp/4.12.0` fails this rule. |
-| E2 | Option chain requests use `mode=cached` unless the use case needs live data. A live chain costs one credit per contract; a cached chain costs one credit. |
+| E2 | Option chain requests use `mode=cached` unless the use case needs live data. A live chain costs one credit per contract; a cached chain costs one credit. Cached mode is available only on paid plans that are not trials. Free Forever and every trial (Starter Trial, Trader Trial, Prime Trial) get a `402` for `mode=cached`, so on a `402` the application repeats the request without `mode`. |
 | E3 | Polling intervals fit a credit budget. A free key holds 100 credits a day. State the worst-case daily credit spend you can derive from the code. |
-| E4 | The application handles `429`, `402`, and `403` with a message to the user. A `403` is the single-IP control and clears after five minutes with no requests. |
+| E4 | The application handles `429`, `402`, and `403` with a message to the user. A `403` is the single-IP control. The block expires five minutes after the IP switch; further requests during the block do not extend it. |
 
 ### Group F — Onboarding and entitlement (all P2)
 
 | ID | The rule |
 |----|----------|
 | F1 | Onboarding tells the user they need a second account, and links to the Market Data sign-up page. |
 | F2 | Onboarding explains the verification step and the wait of up to one business day before real-time data arrives. |
-| F3 | The application works on a delayed, historical, or quota-limited key, and reads response timestamps rather than assuming the data is live. A missing entitlement raises no error: the API returns the freshest data the user is entitled to. |
+| F3 | The application works on a delayed, historical, or quota-limited key, and reads response timestamps rather than assuming the data is live. When the request sends no `mode`, a missing entitlement raises no error: the API returns the freshest data the user is entitled to. A paid plan is also downgraded silently. On a Free Forever or trial key, an explicit `mode=live`, `mode=delayed`, or `mode=eod` returns `402` "Feed not available for your plan.", and so does a date older than the plan allows. The application omits `mode` unless it needs one, and handles the `402`. |
 | F4 | The application does not assume every user is non-professional. A user our compliance team classifies as professional never receives real-time data on a self-service plan. |
 
 ## What is NOT a finding
@@ -220,18 +226,23 @@ Do not report these. Each one is a legitimate design.
 
 A developer server that handles only **historical** data is not BYOK, and it is
 also not automatically a violation. The exchanges charge no redistribution fee
-for historical data, meaning data from a completed session once the next session
-has opened. Delayed data does not qualify.
+for historical data, meaning data from a completed session. Delayed data does not
+qualify.
 
 If you find a server path that carries only historical data, record it as a P1
 against A2, and add a note that the product may qualify under the historical-only
 model. Recommend that the developer contact Market Data sales rather than
 recommending a code change. Say plainly that you cannot grant that model, and
 that only Market Data can.
 
-Data becomes historical at the open of the next trading session. A product that
-serves the previous session's data at 06:00 Eastern is serving delayed data and
-is fee-liable until the bell.
+Stocks and options become historical at different times:
+
+- Stock data becomes historical at 4:15:01 PM Eastern on the session day.
+- Option data becomes historical at 9:30:01 AM Eastern, at the open of the next
+  trading session.
+
+A product that serves the previous session's option data at 06:00 Eastern is
+serving delayed data and is fee-liable until the bell.
 
 ## Search seeds
 

diff --git a/sheets/options/optionchain.md b/sheets/options/optionchain.md
@@ -1,12 +1,12 @@
 ---
 title: OPTIONCHAIN
-description: The OPTIONCHAIN formula fetches a current option chain into your spreadsheet. See the syntax, sample usage and data availability.
+description: The OPTIONCHAIN formula fetches a current or end-of-day historical option chain into your spreadsheet. See the syntax, samples and data availability.
 sidebar_position: 3
 sidebar_custom_props:
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 ---
 
-Fetches a current option chain from Market Data.
+Fetches a current option chain, or the end-of-day option chain of a past trading day, from Market Data.
 
 ## Video Tutorial
 <iframe width="100%" height="503" src="https://www.youtube.com/embed/Pwnsp5SsU3M" title="How To View and Filter The Options Chain" frameborder="0" allow="accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture" allowfullscreen></iframe>
@@ -18,10 +18,16 @@ Fetches a current option chain from Market Data.
 =OPTIONCHAIN("AAPL","all,noheaders","60 DTE","150,160)
 =OPTIONCHAIN("AAPL","all","60 DTE","100-200","calls")
 ```
+### Historical Chains
+```excel-formula
+=OPTIONCHAIN("AAPL","strike,bid,ask","45 DTE","200-250","puts","2026-09-01")
+=OPTIONCHAIN("AAPL",,,,,"last session")
+=OPTIONCHAIN(A2,"strike,bid,ask","45 DTE","200-250","puts",B2)
+```
 
 ## Syntax
 ```excel-formula
-=OPTIONCHAIN(underlying symbol, [attributes], expiration date, [strikes], [filters])
+=OPTIONCHAIN(underlying symbol, [attributes], expiration date, [strikes], [filters], [as of])
 ```
 
 - **underlying symbol** _(REQUIRED)_ Use the stock, etf, or underlying index symbol.
@@ -32,6 +38,7 @@ Fetches a current option chain from Market Data.
   - "side" - Call or put.
   - "strike" - The option's strike price.
   - "first traded" - The date this option first began to trade.
+  - "dte" - Days to expiration: the calendar days until the option expires, counted from today on a current quote and from the quote date on a historical one.
   - "date", "updated" - The date and time of the quote.
   - "bid" – The bid price of the option.
   - "bid size" – The quantity of contracts offered at the bid price.
@@ -55,7 +62,8 @@ Fetches a current option chain from Market Data.
 - **expiration date** - _(OPTIONAL)_ - The expiration date of the option chain. Options from this expiration will be returned. If no value is specified, the next monthly expiration will be used.
   - "date" - A single date in YYYY-MM-DD or MM/DD/YYYY format enclosed between quotes.
   - \[date cell reference] - A cell reference to a date in Sheets.
-  - "dte _number_" - Days to expiry. Return the expiration date most closely matching the indicated number. For example, if today was Jan 1 and you used a DTE of 45, the expiration closest to Feb 15 would be selected.
+  - "dte _number_" - Days to expiry. Return the expiration date most closely matching the indicated number. For example, if today was Jan 1 and you used a DTE of 45, the expiration closest to Feb 15 would be selected. With an **as of** date, the days are counted from that date instead of today.
+  - The expiration date is always the contract's expiration, never the quote date. To see a chain as it was on a past day, use **as of**.
 - **strikes** _(OPTIONAL)_ – Limit the strikes returned from the option chain formula to only the specified strikes or deltas. The formula will assume strikes for numbers greater than 1 and deltas for numbers less than 1 or when the word `delta` is placed before the number(s).
   - \[number] - A single number or a cell reference to a number. Example: `150`
   - \[decimal] - A decimal number will be interpreted as a delta value to be matched and the formula will return the strike that most closely matches the delta provided. Example: `.60`
@@ -68,18 +76,26 @@ Fetches a current option chain from Market Data.
   - "string of decimals" - Seperate multiple deltas with commas. Example: `".50,.60.,70"`
   - "logical expression" - A logical expression. Example: `"<200 delta <.50"`
   - "limit \[number]" - Limit the output to \[number] strikes closest to the money. Example: `"limit 4"`
+  - Deltas are only available for current chains. Selecting strikes by delta together with an **as of** date returns an error; use strikes instead.
 - **filters** _(OPTIONAL)_ – Use specific keywords to further filter the option chain.
   - "call", "calls" - Only return calls.
   - "put", "puts" - Only return puts.
   - "itm", "in the money" - Only return in the money options.
   - "otm", "out of the money" - Only return out of the money options.
   - "nonstandard", "non-standard" - Include non-standard contracts in the optionchain output.
+- **as of** _(OPTIONAL)_ – The quote date. Leave it out for the current chain, or give one past trading day to get that day's end-of-day chain. See [Working With Historical Chains](#working-with-historical-chains).
+  - _(omitted)_ or "current" - The current chain, the same as a formula without this parameter.
+  - "date" - A single date in YYYY-MM-DD or MM/DD/YYYY format enclosed between quotes.
+  - \[date cell reference] - A cell reference to a date in Sheets.
+  - "last session" - The most recent trading day whose end-of-day chain has been published.
+  - "yesterday", "today" - The calendar day before today, or today. On a weekend or holiday these return an error, so "last session" is usually the better choice.
+  - An empty cell or `""` returns an error, not the current chain. To switch a sheet between current and historical chains with one cell, write "current" in it.
 
 ## Usage Information
 
 ### Data Availability
 
-The `OPTIONCHAIN` function fetches current option chain data. The type of data you receive depends on your user type and OPRA entitlement. This may include real-time data, 15-minute delayed data, or historical data, depending on the plan or access level. To get real-time options data, users need to sign the OPRA agreement.
+Without an **as of** date, the `OPTIONCHAIN` function fetches current option chain data. The type of data you receive depends on your user type and OPRA entitlement. This may include real-time data, 15-minute delayed data, or historical data, depending on the plan or access level. To get real-time options data, users need to sign the OPRA agreement.
 
 | User Type        | OPRA Entitlement | Data Type              |
 |------------------|------------------|------------------------|
@@ -89,6 +105,17 @@ The `OPTIONCHAIN` function fetches current option chain data. The type of data y
 | Professional     | ❌               | Historical (1 day old) |
 | Unknown          | Any              | Historical (1 day old) |
 
+### Working With Historical Chains
+
+With an **as of** date, `OPTIONCHAIN` returns the chain as it closed on that trading day.
+
+- Only end-of-day chains are available. There are no intraday snapshots, and only one date per formula.
+- The columns are the same as for a current chain. Implied volatility and the greeks (delta, gamma, theta, vega) are blank, and selecting strikes by delta is not available.
+- Open interest is the figure settled out of the previous session, as described under the "open interest" attribute.
+- A date in the future, a weekend or a market holiday returns an error. Today's chain returns a "not available yet" error until the end-of-day chain is published after the close.
+- A relative date such as "last session" is resolved when the formula calculates. It updates when the sheet is refreshed or a referenced cell changes, not on its own as days pass.
+- Historical data is subject to your plan's limits. [Learn more about plan limits](/account/plan-limits).
+
 :::info[What are entitlements?]
 Entitlements are permissions granted by exchanges that allow access to their data. To get real-time options data, users need to sign the [OPRA agreement](/account/entitlements). [Learn more about entitlements](/account/entitlements).
 :::