Gemini Predictions

Gemini Predictions is a centralized prediction market run by Gemini. Like Kalshi, it uses traditional limit-order semantics with server-side authentication — no client-side signing needed.

At a glance


Chain	None (centralized exchange)
Wallet model	None (USD account balance)
Quote token	USD
Signing	Server-side (HMAC-SHA512)
Auth	Gemini API key + HMAC secret, registered once

Prerequisites

A Gemini account with Predictions enabled
A Gemini API key with order placement permissions — generate at exchange.gemini.com (or exchange.sandbox.gemini.com for testing)
Save the API key and HMAC secret immediately — Gemini only shows the secret once

One-time setup: register credentials

import { DelphiClient } from '@delphimarkets/sdk';

const client = new DelphiClient({
  apiKey: process.env.DELPHI_API_KEY!,
  baseUrl: 'https://api.delphiterminal.co',
});

await client.registerCredentials('gemini', {
  api_key: process.env.GEMINI_API_KEY!,
  api_secret: process.env.GEMINI_API_SECRET!,  // HMAC-SHA512 secret
  api_passphrase: '',                           // unused for Gemini
});

The Delphi server stores the HMAC secret encrypted at rest and uses it to sign every Gemini request.

Place an order

import { DelphiClient, buildGeminiOrder } from '@delphimarkets/sdk';

const order = await client.placeOrder({
  exchange: 'gemini',
  market_id: 'GEMI-FEDJAN26-DN25',
  order_type: 'GTC',
  signed_order: buildGeminiOrder({
    symbol: 'GEMI-FEDJAN26-DN25',
    side: 'buy',          // 'buy' or 'sell'
    outcome: 'yes',       // 'yes' or 'no'
    quantity: 1,           // number of contracts
    price: 0.55,           // limit price, 0.01 to 0.99
    timeInForce: 'good-til-cancel', // optional, this is the default
  }),
});

console.log(`Placed: ${order.order_id} (${order.status})`);

buildGeminiOrder is a thin convenience helper — it just shapes your input into the JSON the API expects. There’s no cryptography happening client-side; you can construct the payload by hand if you prefer:

const order = await client.placeOrder({
  exchange: 'gemini',
  market_id: 'GEMI-FEDJAN26-DN25',
  order_type: 'GTC',
  signed_order: {
    symbol: 'GEMI-FEDJAN26-DN25',
    side: 'buy',
    outcome: 'yes',
    quantity: '1',
    price: '0.55',
    time_in_force: 'good-til-cancel',
  },
});

Order parameters

Field	Type	Description
`symbol`	`string`	Gemini contract symbol (e.g. `GEMI-FEDJAN26-DN25`).
`side`	`'buy' \| 'sell'`	Buy to enter long, sell to enter short or close.
`outcome`	`'yes' \| 'no'`	Which outcome of the market.
`quantity`	`number`	Number of contracts.
`price`	`number`	Limit price in [0.01, 0.99].
`timeInForce`	`string?`	Default `'good-til-cancel'`. Other Gemini values: `'fill-or-kill'`, `'immediate-or-cancel'`.

Query and cancel

const status = await client.getOrder(order.order_id, 'gemini');
const all = await client.listOrders('gemini');
await client.cancelOrder(order.order_id, 'gemini');

Common pitfalls

401 Unauthorized when placing first order

Confirm your API key has the Trader role (or Auditor + Trader) on Gemini. Read-only Auditor-tier keys can fetch market data but can’t place orders.

HMAC secret got rotated and orders fail

Gemini lets you rotate the HMAC secret while keeping the same API key ID. If you rotate, re-register on Delphi with the new secret:

await client.registerCredentials('gemini', {
  api_key: process.env.GEMINI_API_KEY!,
  api_secret: process.env.GEMINI_API_SECRET_NEW!,
  api_passphrase: '',
});

Sandbox vs production

The Delphi server points at production Gemini by default. Sandbox API keys (from exchange.sandbox.gemini.com) won’t work without server-side configuration. Contact Delphi support if you need sandbox routing.

Symbol format

Gemini contract symbols include the expiry encoded in the suffix (e.g. FEDJAN26 = Fed meeting January 2026). Always pull the latest active symbols from Gemini’s market data endpoint before placing orders — old symbols will return “market not found” once they settle.

API reference

POST /api/v1/orders — accepts a GeminiPredictionOrder in signed_order
POST /api/v1/users/{userID}/credentials — pass _ as the path segment

Trading SDK

Trading API

Credentials

Polymarket Onboarding

At a glance

Prerequisites

One-time setup: register credentials

Place an order

Order parameters

Query and cancel

Common pitfalls

API reference

​At a glance

​Prerequisites

​One-time setup: register credentials

​Place an order

​Order parameters

​Query and cancel

​Common pitfalls

​API reference

At a glance

Prerequisites

One-time setup: register credentials

Place an order

Order parameters

Query and cancel

Common pitfalls

API reference