Reprice a resting limit order in place
Moves a resting limit order’s price in one venue round trip. The order keeps its Kairos order_id AND its venue exchange_order_id — that is the property this endpoint exists to provide: no supersession to record, and no second order whose fill could be booked twice. The cancel-and-replace it replaces leaves the book empty of the order for the whole cancel round trip and mints a second id to reconcile.
Venue support. Only venues advertising supports_native_amend in GET /exchanges/{exchange_id}/capabilities — today kalshi alone. Anything else is 409 EXCHANGE_AMEND_UNSUPPORTED, answered before the order’s own state is inspected so the verdict is a permanent property of the venue rather than of this moment. There is deliberately NO internal cancel-and-replace fallback: that substitution changes queue position, order identity and the caller’s failure modes, so it is the caller’s decision.
Reprice only. quantity is accepted solely to be refused with 409 EXCHANGE_AMEND_QUANTITY_UNSUPPORTED, before the order is read — refused rather than silently ignored so a caller never believes it resized. Limit orders only; price must be strictly between 0 and 1, in the order’s own outcome’s terms.
This endpoint almost always returns 200. success: false is an ambiguous venue outcome, never a transport failure — the same convention POST /orders/{order_id}/cancel uses, because a 5xx invites a retry against an order that may already have been amended. It covers a terminal order, an order not yet at the venue, and a venue that refused; on every one of those the order is untouched and still resting on its old price. Branch on success, not on the status code.
Queue position. Kalshi preserves it only when an amend DECREASES size; a reprice forfeits it — but so does the cancel/replace this replaces, so nothing is lost. The win is the closed off-book window, not priority.
Admission. Runs the same checks a submit does — kill switch, side/kind/TIF circuit breakers evaluated against the order’s own side and kind (an amend changes neither), and the order rate limit. An immediate fill from a crossing amend is booked through the normal poller path, not from this response.
Auth & scope. Requires trade:execute and ownership of the order.
curl --request POST \
--url https://execution.kairos.trade/orders/{order_id}/amend \
--header 'Content-Type: application/json' \
--header 'X-Api-Key: <api-key>' \
--header 'X-Api-Secret: <api-key>' \
--header 'X-Client-Id: <api-key>' \
--data '
{
"price": 123,
"quantity": 123
}
'import requests
url = "https://execution.kairos.trade/orders/{order_id}/amend"
payload = {
"price": 123,
"quantity": 123
}
headers = {
"X-Client-Id": "<api-key>",
"X-Api-Key": "<api-key>",
"X-Api-Secret": "<api-key>",
"Content-Type": "application/json"
}
response = requests.post(url, json=payload, headers=headers)
print(response.text)const options = {
method: 'POST',
headers: {
'X-Client-Id': '<api-key>',
'X-Api-Key': '<api-key>',
'X-Api-Secret': '<api-key>',
'Content-Type': 'application/json'
},
body: JSON.stringify({price: 123, quantity: 123})
};
fetch('https://execution.kairos.trade/orders/{order_id}/amend', options)
.then(res => res.json())
.then(res => console.log(res))
.catch(err => console.error(err));<?php
$curl = curl_init();
curl_setopt_array($curl, [
CURLOPT_URL => "https://execution.kairos.trade/orders/{order_id}/amend",
CURLOPT_RETURNTRANSFER => true,
CURLOPT_ENCODING => "",
CURLOPT_MAXREDIRS => 10,
CURLOPT_TIMEOUT => 30,
CURLOPT_HTTP_VERSION => CURL_HTTP_VERSION_1_1,
CURLOPT_CUSTOMREQUEST => "POST",
CURLOPT_POSTFIELDS => json_encode([
'price' => 123,
'quantity' => 123
]),
CURLOPT_HTTPHEADER => [
"Content-Type: application/json",
"X-Api-Key: <api-key>",
"X-Api-Secret: <api-key>",
"X-Client-Id: <api-key>"
],
]);
$response = curl_exec($curl);
$err = curl_error($curl);
curl_close($curl);
if ($err) {
echo "cURL Error #:" . $err;
} else {
echo $response;
}package main
import (
"fmt"
"strings"
"net/http"
"io"
)
func main() {
url := "https://execution.kairos.trade/orders/{order_id}/amend"
payload := strings.NewReader("{\n \"price\": 123,\n \"quantity\": 123\n}")
req, _ := http.NewRequest("POST", url, payload)
req.Header.Add("X-Client-Id", "<api-key>")
req.Header.Add("X-Api-Key", "<api-key>")
req.Header.Add("X-Api-Secret", "<api-key>")
req.Header.Add("Content-Type", "application/json")
res, _ := http.DefaultClient.Do(req)
defer res.Body.Close()
body, _ := io.ReadAll(res.Body)
fmt.Println(string(body))
}HttpResponse<String> response = Unirest.post("https://execution.kairos.trade/orders/{order_id}/amend")
.header("X-Client-Id", "<api-key>")
.header("X-Api-Key", "<api-key>")
.header("X-Api-Secret", "<api-key>")
.header("Content-Type", "application/json")
.body("{\n \"price\": 123,\n \"quantity\": 123\n}")
.asString();require 'uri'
require 'net/http'
url = URI("https://execution.kairos.trade/orders/{order_id}/amend")
http = Net::HTTP.new(url.host, url.port)
http.use_ssl = true
request = Net::HTTP::Post.new(url)
request["X-Client-Id"] = '<api-key>'
request["X-Api-Key"] = '<api-key>'
request["X-Api-Secret"] = '<api-key>'
request["Content-Type"] = 'application/json'
request.body = "{\n \"price\": 123,\n \"quantity\": 123\n}"
response = http.request(request)
puts response.read_body{
"success": true,
"order_id": "3c90c3cc-0d44-4b50-8888-8dd25736052a",
"exchange_order_id": "<string>",
"price": "<string>",
"quantity": "<string>",
"message": "<string>"
}{
"error": "<string>",
"error_details": {
"code": "FUNDS_INSUFFICIENT_USDC",
"message": "<string>",
"actions": [
{
"action": "enable_trading",
"label": "Add Funds",
"primary": true,
"url": "<string>"
}
],
"details": "<string>",
"metadata": {}
},
"code": "<string>"
}{
"error": "Unauthorized"
}{
"error": "<string>",
"error_details": {
"code": "FUNDS_INSUFFICIENT_USDC",
"message": "<string>",
"actions": [
{
"action": "enable_trading",
"label": "Add Funds",
"primary": true,
"url": "<string>"
}
],
"details": "<string>",
"metadata": {}
},
"code": "<string>"
}{
"error": "<string>",
"error_details": {
"code": "FUNDS_INSUFFICIENT_USDC",
"message": "<string>",
"actions": [
{
"action": "enable_trading",
"label": "Add Funds",
"primary": true,
"url": "<string>"
}
],
"details": "<string>",
"metadata": {}
},
"code": "<string>"
}{
"error": "<string>",
"error_details": {
"code": "FUNDS_INSUFFICIENT_USDC",
"message": "<string>",
"actions": [
{
"action": "enable_trading",
"label": "Add Funds",
"primary": true,
"url": "<string>"
}
],
"details": "<string>",
"metadata": {}
},
"code": "<string>"
}{
"error": "<string>",
"error_details": {
"code": "FUNDS_INSUFFICIENT_USDC",
"message": "<string>",
"actions": [
{
"action": "enable_trading",
"label": "Add Funds",
"primary": true,
"url": "<string>"
}
],
"details": "<string>",
"metadata": {}
},
"code": "<string>"
}{
"error": "<string>",
"error_details": {
"code": "FUNDS_INSUFFICIENT_USDC",
"message": "<string>",
"actions": [
{
"action": "enable_trading",
"label": "Add Funds",
"primary": true,
"url": "<string>"
}
],
"details": "<string>",
"metadata": {}
},
"code": "<string>"
}{
"error": "<string>",
"error_details": {
"code": "FUNDS_INSUFFICIENT_USDC",
"message": "<string>",
"actions": [
{
"action": "enable_trading",
"label": "Add Funds",
"primary": true,
"url": "<string>"
}
],
"details": "<string>",
"metadata": {}
},
"code": "<string>"
}Authorizations
Credential client id (kairos_ck_...). Must be sent together with X-Api-Key and X-Api-Secret.
64-char hex API key.
64-char hex API secret.
Path Parameters
Internal Kairos order id.
Body
Request body for POST /orders/{order_id}/amend. Reprice only — quantity exists solely to be refused.
New limit price, strictly greater than 0 and less than 1, in the order's OWN outcome's terms (send a Kalshi No order's No price; do not complement it client-side). Omitted re-sends the price the order already has.
Accepted only to be REFUSED with 409 EXCHANGE_AMEND_QUANTITY_UNSUPPORTED, before the order is even read. This route reprices; it does not resize. Refused rather than ignored so a caller never believes an order was resized when it was not.
Response
Amend outcome. Check success — a 200 does not guarantee the order was actually amended (see description).
Response for POST /orders/{order_id}/amend. Returned with HTTP 200 even when success is false.
Whether the venue confirmed the amend. false is an AMBIGUOUS outcome, not an error status — the amend may have been refused, or it may have reached the venue and been applied without us learning so. That ambiguity is why it is not a 5xx, which would invite a blind retry against an order that may already carry the new price. A non-amendable status answers 200 with a false success too. On any false, re-read the order before acting on it.
The id that was addressed, always unchanged. An amend never mints a new order.
The venue's order id, also unchanged — Kalshi AmendOrder v2 answers with the same id it was given, so there is no supersession to record. Omitted only on the pre-submission path, where the order has no venue identity yet.
Decimal string. The new resting price on success. On an unsuccessful path it is the price we last recorded — the resting price when the venue explicitly refused, but only our last known value when the call failed in transit or came back unreadable, where the venue may in fact hold the new price. Omitted when unknown.
Decimal string, the order's total size — always the size it was placed for. This route never resizes. Omitted when unknown.
Human-readable outcome detail, e.g. "Order amended on exchange", "Order cannot be amended - status is filled", or "Could not amend on the exchange: ". A success whose row write failed reads "Order amended on exchange (price not persisted)".
Was this page helpful?
curl --request POST \
--url https://execution.kairos.trade/orders/{order_id}/amend \
--header 'Content-Type: application/json' \
--header 'X-Api-Key: <api-key>' \
--header 'X-Api-Secret: <api-key>' \
--header 'X-Client-Id: <api-key>' \
--data '
{
"price": 123,
"quantity": 123
}
'import requests
url = "https://execution.kairos.trade/orders/{order_id}/amend"
payload = {
"price": 123,
"quantity": 123
}
headers = {
"X-Client-Id": "<api-key>",
"X-Api-Key": "<api-key>",
"X-Api-Secret": "<api-key>",
"Content-Type": "application/json"
}
response = requests.post(url, json=payload, headers=headers)
print(response.text)const options = {
method: 'POST',
headers: {
'X-Client-Id': '<api-key>',
'X-Api-Key': '<api-key>',
'X-Api-Secret': '<api-key>',
'Content-Type': 'application/json'
},
body: JSON.stringify({price: 123, quantity: 123})
};
fetch('https://execution.kairos.trade/orders/{order_id}/amend', options)
.then(res => res.json())
.then(res => console.log(res))
.catch(err => console.error(err));<?php
$curl = curl_init();
curl_setopt_array($curl, [
CURLOPT_URL => "https://execution.kairos.trade/orders/{order_id}/amend",
CURLOPT_RETURNTRANSFER => true,
CURLOPT_ENCODING => "",
CURLOPT_MAXREDIRS => 10,
CURLOPT_TIMEOUT => 30,
CURLOPT_HTTP_VERSION => CURL_HTTP_VERSION_1_1,
CURLOPT_CUSTOMREQUEST => "POST",
CURLOPT_POSTFIELDS => json_encode([
'price' => 123,
'quantity' => 123
]),
CURLOPT_HTTPHEADER => [
"Content-Type: application/json",
"X-Api-Key: <api-key>",
"X-Api-Secret: <api-key>",
"X-Client-Id: <api-key>"
],
]);
$response = curl_exec($curl);
$err = curl_error($curl);
curl_close($curl);
if ($err) {
echo "cURL Error #:" . $err;
} else {
echo $response;
}package main
import (
"fmt"
"strings"
"net/http"
"io"
)
func main() {
url := "https://execution.kairos.trade/orders/{order_id}/amend"
payload := strings.NewReader("{\n \"price\": 123,\n \"quantity\": 123\n}")
req, _ := http.NewRequest("POST", url, payload)
req.Header.Add("X-Client-Id", "<api-key>")
req.Header.Add("X-Api-Key", "<api-key>")
req.Header.Add("X-Api-Secret", "<api-key>")
req.Header.Add("Content-Type", "application/json")
res, _ := http.DefaultClient.Do(req)
defer res.Body.Close()
body, _ := io.ReadAll(res.Body)
fmt.Println(string(body))
}HttpResponse<String> response = Unirest.post("https://execution.kairos.trade/orders/{order_id}/amend")
.header("X-Client-Id", "<api-key>")
.header("X-Api-Key", "<api-key>")
.header("X-Api-Secret", "<api-key>")
.header("Content-Type", "application/json")
.body("{\n \"price\": 123,\n \"quantity\": 123\n}")
.asString();require 'uri'
require 'net/http'
url = URI("https://execution.kairos.trade/orders/{order_id}/amend")
http = Net::HTTP.new(url.host, url.port)
http.use_ssl = true
request = Net::HTTP::Post.new(url)
request["X-Client-Id"] = '<api-key>'
request["X-Api-Key"] = '<api-key>'
request["X-Api-Secret"] = '<api-key>'
request["Content-Type"] = 'application/json'
request.body = "{\n \"price\": 123,\n \"quantity\": 123\n}"
response = http.request(request)
puts response.read_body{
"success": true,
"order_id": "3c90c3cc-0d44-4b50-8888-8dd25736052a",
"exchange_order_id": "<string>",
"price": "<string>",
"quantity": "<string>",
"message": "<string>"
}{
"error": "<string>",
"error_details": {
"code": "FUNDS_INSUFFICIENT_USDC",
"message": "<string>",
"actions": [
{
"action": "enable_trading",
"label": "Add Funds",
"primary": true,
"url": "<string>"
}
],
"details": "<string>",
"metadata": {}
},
"code": "<string>"
}{
"error": "Unauthorized"
}{
"error": "<string>",
"error_details": {
"code": "FUNDS_INSUFFICIENT_USDC",
"message": "<string>",
"actions": [
{
"action": "enable_trading",
"label": "Add Funds",
"primary": true,
"url": "<string>"
}
],
"details": "<string>",
"metadata": {}
},
"code": "<string>"
}{
"error": "<string>",
"error_details": {
"code": "FUNDS_INSUFFICIENT_USDC",
"message": "<string>",
"actions": [
{
"action": "enable_trading",
"label": "Add Funds",
"primary": true,
"url": "<string>"
}
],
"details": "<string>",
"metadata": {}
},
"code": "<string>"
}{
"error": "<string>",
"error_details": {
"code": "FUNDS_INSUFFICIENT_USDC",
"message": "<string>",
"actions": [
{
"action": "enable_trading",
"label": "Add Funds",
"primary": true,
"url": "<string>"
}
],
"details": "<string>",
"metadata": {}
},
"code": "<string>"
}{
"error": "<string>",
"error_details": {
"code": "FUNDS_INSUFFICIENT_USDC",
"message": "<string>",
"actions": [
{
"action": "enable_trading",
"label": "Add Funds",
"primary": true,
"url": "<string>"
}
],
"details": "<string>",
"metadata": {}
},
"code": "<string>"
}{
"error": "<string>",
"error_details": {
"code": "FUNDS_INSUFFICIENT_USDC",
"message": "<string>",
"actions": [
{
"action": "enable_trading",
"label": "Add Funds",
"primary": true,
"url": "<string>"
}
],
"details": "<string>",
"metadata": {}
},
"code": "<string>"
}{
"error": "<string>",
"error_details": {
"code": "FUNDS_INSUFFICIENT_USDC",
"message": "<string>",
"actions": [
{
"action": "enable_trading",
"label": "Add Funds",
"primary": true,
"url": "<string>"
}
],
"details": "<string>",
"metadata": {}
},
"code": "<string>"
}