Interactive Brokers API vs Alpaca for Automation

Alpaca vs IBKR at a glance: interfaces, limits and testing

Official documentation checked on 12 October 2026. These are documented integration facts, not an IMRYN execution benchmark or a fee comparison.

The short verdict: Alpaca or Interactive Brokers?

Pick Alpaca when your automation trades US stocks, ETFs, options or crypto and you want working code quickly. Its Trading API comes with SDKs, a paper-only account needs only an email address, and Alpaca states that the API spec is the same for paper and live accounts.

Pick Interactive Brokers when the strategy needs more than that. IBKR describes trading global stocks, options, futures, currencies and more from a single platform, and notes that not every product is available in every country or to every client. The price is a heavier connection model: a running TWS or IB Gateway for the TWS API, or Client Portal Gateway or OAuth for the Web API.

Neither API decides whether a strategy is sound. This page compares documented integration facts checked on 12 October 2026. It is not a test of execution quality, fees or returns.

How each API connects your code to the broker

Alpaca authenticates Trading API calls with API keys, and your paper account has a different key from your live account. Moving to paper means replacing the key and the base URL, for example https://paper-api.alpaca.markets. Every Trading API response carries an X-Request-ID header, which Alpaca asks for in support requests, so log it with each order call.

The IBKR Web API is a REST interface over HTTPS with JSON messages. Individual accounts authenticate through Client Portal Gateway, a Java client that reverse-proxies the login through SSO. You log in from a browser on the same machine, and every API call must come from the machine where the gateway was authenticated. OAuth 1.0a is the only method for third-party developers, and OAuth 2.0 serves advisor, broker and institutional account types.

The TWS API is a TCP socket protocol that talks to Trader Workstation or IB Gateway, so one of them must be running. IBKR provides code in Python, Java, C++, C# and Visual Basic, and lists a funded and opened IBKR Pro account as a requirement, with Python 3.11 as the minimum Python release. It also warns that a feature missing from TWS is missing from the API.

Rate limits that shape an automated loop

On the IBKR Web API, the global limit is 10 requests per second for each authenticated username, which means each Web API session. Some endpoints are tighter: /iserver/orders and /iserver/trades allow 1 request every 5 seconds. Going over returns HTTP 429, and the offending IP address can be put in a penalty box for 10 minutes.

On the TWS API, the request limit per second equals your market data lines divided by 2. With the default 100 lines, that is 50 requests per second. IBKR points heavier users to its FIX API, limited to 250 messages per second through IB Gateway.

Alpaca publishes call limits by market data plan: 200 historical API calls per minute on the free Basic plan and 10,000 per minute on Algo Trader Plus. Size polling, retries and backoff for the plan or session you actually use, not for the best case.

Paper trading: who can test, and what it hides

Alpaca paper trading is free, and anyone globally can open a paper-only account. It starts with a $100k balance by default and can be reset. Fills are simulated from real-time quotes, and Alpaca lists what the simulation leaves out: market impact, information leakage, slippage due to latency, queue position for non-marketable limit orders, regulatory fees and dividends.

An IBKR paper account opens once your regular account has been approved and funded. It offers the full range of trading facilities in a simulated environment, but IBKR says it relies on more simulated technologies than live trading, so order execution may vary. The Web API has no live or paper switch: you log in to Client Portal Gateway with your separate paper username.

In both cases, a paper result validates the plumbing, not the strategy. Test the order states and error paths you expect to meet live.

Market data: what is free and what you pay for

Alpaca’s Basic plan is free. It serves real-time equities from IEX only, an indicative feed for options, 30 symbols on the stock WebSocket, and historical data that excludes the latest 15 minutes. Algo Trader Plus, at $99 a month, covers all US stock exchanges and the OPRA options feed.

IBKR states that a paid data subscription is required for all API market data except delayed watchlist data. In the TWS API you set the data type for a request: live, frozen, delayed or delayed frozen. Check which type you received before an automated rule uses the price.

Keeping an automated session alive

TWS and IB Gateway shut down at a time set under Lock and Exit. For API users, IBKR recommends Never lock Trader Workstation and Auto restart. The weekly authentication cycle starts every Monday, and a Soft token=0 login failure means you must log in again manually. Decide in advance who handles that step.

IBKR also notes that Interactive Brokers Canada does not allow your own application to submit orders through the API for products traded on a Canadian marketplace. On Alpaca, extended hours accept only limit orders with a day or gtc time in force, and the overnight session runs from 8:00pm to 4:00am ET, Sunday to Friday.

Checklist before you automate with either API

Run these checks against your own account and jurisdiction before the first live order.

• List the instruments and markets the strategy needs, then confirm each one is available to your account and country.
• Write down the rate limit of your session or plan, and keep polling and retries below it.
• Decide where the session lives: an always-on gateway for IBKR, or keys stored as secrets for Alpaca.
• Run the full order lifecycle in paper trading, including rejections, partial fills and cancels.
• Confirm which feed or data type each price comes from before a rule acts on it.
• Log every request with its timestamp and identifier, including Alpaca’s X-Request-ID.
• Keep a manual stop that still works when the API or the gateway is down.

Where IMRYN fits

IMRYN is systematic trading infrastructure in development, built around risk limits, real-time alerts, emergency stops and continuous human oversight. A broker API sits underneath that layer. It carries orders, it does not decide whether an order should exist.

IMRYN does not rank brokers or promise results. Execution events and model decisions are recorded so they can be inspected. This is not investment advice, and trading involves risk, including loss of capital.