HIP-1313 Update REST API (#1374)

Signed-off-by: Steven Sheehy <steven.sheehy@swirldslabs.com>

Author: steven-sheehy

HIP/hip-1313.md

@@ -11,7 +11,7 @@ needs-hedera-review: Yes
 status: Last Call
 last-call-date-time: 2025-12-30T07:00:00Z
 created: 2025-10-17
-updated: 2025-12-16
+updated: 2026-01-16
 requires: 1261
 ---
 
@@ -316,8 +316,28 @@ For high-volume transactions:
 ## Mirror Node Changes
 1. Add high volume fields to relevant APIs (e.g. `/api/v1/transactions`,
    `/api/v1/transactions/{id}` and the list of transactions
-   within `/api/v1/accounts/{id}`)
-2. Incorporate high volume as an estimation option in fee estimation.
+   within `/api/v1/accounts/{id}`). An example response is shown below with
+other fields omitted:
+   ```json
+   {
+     ...
+     "high_volume": true
+   }
+   ```
+
+2. Incorporate high volume as an estimation option in fee estimation. The existing
+   fee estimate JSON response will be enhanced to add a new `high_volume_multiplier` field.
+   The actual totals in the response will not be multiplied by the multiplier.
+   If users want to see how their fees are impacted by high volume pricing they only need
+   to multiply the fee `total` by the new multiplier to get the final pricing. This allows
+   users to get both the regular and high-volume pricing with a single call and simplifies
+   the API by not requiring another parameter.
+   ```json
+   {
+     ...
+     "high_volume_multiplier": 100
+   }
+   ```
 
 ## Backwards Compatibility
 No changes for transactions without the `high_volume` flag. Existing