Documentation Index
Fetch the complete documentation index at: https://docs.kalshi.com/llms.txt
Use this file to discover all available pages before exploring further.
API Key Setup
FIX API keys use the same RSA key pair as the REST API. Generate a 2048-bit RSA key pair and register the public key in your account profile. The resulting API Key ID (UUID) is your SenderCompID.
openssl genpkey -algorithm RSA -pkeyopt rsa_keygen_bits:2048 -out kalshi-fix.key
openssl rsa -in kalshi-fix.key -pubout -out kalshi-fix.pub
Logon (35=A)
The initiator sends a Logon message. The acceptor responds with either a Logon (success) or Logout (failure).
Required Fields
| Tag | Name | Description | Value |
|---|
| 98 | EncryptMethod | Method of encryption | None<0> |
| 96 | RawData | Client logon message signature | Base64 encoded signature |
| 108 | HeartbeatInt | Heartbeat interval (seconds) | N > 3 |
| 1137 | DefaultApplVerID | Default application version | FIX50SP2<9> |
Optional Fields
| Tag | Name | Description | Default |
|---|
| 141 | ResetSeqNumFlag | Reset sequence numbers on logon. Must be Y for KalshiNR, KalshiDC, KalshiPT. | N |
| 8013 | CancelOrdersOnDisconnect | Cancel orders on any disconnection (including graceful logout) | N |
| 20126 | ListenerSession | Listen-only session. KalshiNR/RT only, requires SkipPendingExecReports=Y. | N |
| 20127 | ReceiveSettlementReports | Receive settlement reports. KalshiRT only. | N |
| 20200 | MessageRetentionPeriod | How long session messages will be stored for retransmission, max of 72 hours. KalshiRT and KalshiRFQ only. | 24 |
| 21005 | UseDollars | Enable dollar-based price format for prices, including subpenny precision | N |
| 21011 | SkipPendingExecReports | Skip PENDING_{NEW|REPLACE|CANCEL} execution reports | N |
| 21012 | UseExpiredOrdStatus | Emit Expired<C> (150/39) for expiry-style system cancellations (CloseCancel and OrderExpiryCancel) instead of Canceled<4> | N |
| 21007 | EnableIocCancelReport | Partially filled IOC orders produce a cancel report | N |
| 21008 | PreserveOriginalOrderQty | OrderQty tag 38 always reflects original order quantity across all states | N |
Signature Generation
The RawData field must contain a PSS RSA signature of the pre-hash string:
PreHashString = SendingTime + SOH + MsgType + SOH + MsgSeqNum + SOH + SenderCompID + SOH + TargetCompID
SendingTime in SignatureThe SendingTime in the PreHashString must match exactly the value in field 52 of the Logon message. Format: YYYYMMDD-HH:MM:SS.mmm.SendingTime must be within 30 seconds of the server’s current time, or the message will be rejected with SessionRejectReason<373>=10.
from base64 import b64encode
from Cryptodome.Signature import pss
from Cryptodome.Hash import SHA256
from Cryptodome.PublicKey import RSA
private_key = RSA.import_key(open('kalshi-fix.key').read().encode('utf-8'))
sending_time = "20230809-05:28:18.035"
msg_type = "A"
msg_seq_num = "1"
sender_comp_id = "your-fix-api-key-uuid"
target_comp_id = "Kalshi" # Or appropriate TargetCompID
msg_string = chr(1).join([
sending_time, msg_type, msg_seq_num,
sender_comp_id, target_comp_id
])
msg_hash = SHA256.new(msg_string.encode('utf-8'))
signature = pss.new(private_key).sign(msg_hash)
raw_data_value = b64encode(signature).decode('utf-8')
Heartbeat & Sequence Numbers
| Behavior | Detail |
|---|
| Default heartbeat interval | 30 seconds |
| Missed heartbeat | Connection terminates if heartbeat response not received within interval |
| Sequence number lower than expected | Connection terminated |
| Sequence number higher than expected | Recoverable with ResendRequest (KalshiRT only) |
Message Retransmission
Message retransmission (ResendRequest, SequenceReset) is only supported on KalshiRT and KalshiRFQ.
For all other sessions, ResetSeqNumFlag<141> in the Logon message must always be Y or the Logon will be rejected.
ResendRequest (35=2)
KalshiRT only. Lookback window limited to 24 hours (or up to 72 hours if MessageRetentionPeriod was set on Logon).
| Tag | Name | Description |
|---|
| 7 | BeginSeqNo | Lower bound (inclusive) |
| 16 | EndSeqNo | Upper bound (inclusive) |
Logout (35=5)
Either side may initiate a Logout. The counterparty responds with a Logout, and the transport connection is terminated. If CancelOrdersOnDisconnect=Y was set on Logon, all open orders are canceled.