Alpaca vs Marcus Invest: Which Is Better in 2026?

Figures and features are point-in-time and change; treat the table as a starting map, not a live quote.

A developer-first brokerage with an official MCP server for real-time data, paper trading, and execution by AI agents. Best for people who code.

How it works: Alpaca is a brokerage you talk to through code: a REST and websocket API exposes market data, paper trading, and live commission-free execution, and its official MCP server lets an AI agent pull data, test in a paper account, and place real orders programmatically. You build (or wire up an agent against) that API rather than tapping buttons in an app.

In practice, Alpaca’s AI official mcp server (data + execution). It falls under for builders: connect a broker to an ai agent, which makes it best suited to developers building ai agents. On connecting an account it is “Alpaca accounts”, and on execution it is “Read + trade + paper”. It is priced as free (open source).

One honest limitation: Developer-first; requires code and self-hosting.

Goldman Sachs' automated investing service, built around model ETF portfolios and sold alongside Marcus savings products.

How it works: A questionnaire sets a risk level, and Marcus invests in a diversified ETF portfolio built by Goldman Sachs, rebalancing automatically. The pitch is the pairing with Marcus high-yield savings so cash and investments sit in one place, rather than any distinctive portfolio approach.

In practice, Marcus Invest’s AI automates a diversified etf portfolio. It falls under hands-off automated investing (robo-advisors), which makes it best suited to goldman-built portfolios alongside a marcus savings account. On connecting an account it is “No (holds your money at Marcus)”, and on execution it is “Automated”. It is priced as percentage of assets (verify current).

One honest limitation: A conventional automated portfolio with no distinguishing feature beyond sitting next to Marcus savings.

The core difference is category. Alpaca focuses on developers building ai agents (official mcp server (data + execution)), and Marcus Invest on goldman-built portfolios alongside a marcus savings account (automates a diversified etf portfolio). On broker connection they differ too: Alpaca is “Alpaca accounts” versus Marcus Invest at “No (holds your money at Marcus)”. That shapes everything downstream: how personal the answers are, where trades settle, and how much control you keep over individual positions.

Every tool gives something up for what it does well. Here is the honest give-and-take on each, so you can weigh the specific strengths against the limitations that come with them rather than judging on the headline category alone.

For AI investing tools, the distinction that matters most is whether the tool works from your actual, connected positions or reasons from something else: a separate account it manages for you, or the tickers and numbers you feed it. It decides how personal the answers can be, and where your money physically lives.

• Alpaca: connects specific supported accounts. Alpaca connects a defined set of accounts (Alpaca accounts), so whether it can see your holdings depends on whether your money is at one of them.
• Marcus Invest: manages a separate account it holds. Marcus Invest does not read the brokerage you already use. It opens and holds a new account, then invests the money you move into it, so its view is limited to what sits inside Marcus Invest.

This is where they diverge most. One works from your real, connected account while the other does not, so if you want an assistant grounded in the exact positions you already hold, that gap is the thing to weigh first. This holdings-aware angle is the one Walnut is built around: it connects the brokerage you already use and reasons from your live positions, read-only by default, with any trades left for you to approve.

There is no universal winner here; the right pick depends on the job you are hiring the tool for. Match the category to your intent rather than chasing a single “best.”

• Choose Alpaca if you want developers building ai agents. Its AI official mcp server (data + execution), it is priced as free (open source), and it fits for builders: connect a broker to an ai agent. It is built for developers building their own automated or AI-driven trading systems. Keep in mind that developer-first; requires code and self-hosting.
• Choose Marcus Invest if you want goldman-built portfolios alongside a marcus savings account. Its AI automates a diversified etf portfolio, it is priced as percentage of assets (verify current), and it fits hands-off automated investing (robo-advisors). It is built for an existing Marcus savings customer who wants automated investing in the same place and does not need anything unusual. Keep in mind that a conventional automated portfolio with no distinguishing feature beyond sitting next to marcus savings.

Because they sit in different categories, this is not strictly either-or: some investors use one for developers building ai agents and the other for goldman-built portfolios alongside a marcus savings account, and just watch for overlapping costs.

Cost is easy to misread when two tools charge in different shapes, so compare the model, not just the number. Alpaca is priced as free (open source), while Marcus Invest is priced as percentage of assets (verify current). A percentage-of-assets fee scales with your balance, a flat subscription does not, and a “free” tier usually earns elsewhere (on cash, order flow, or premium upgrades), so the cheapest headline is not always the cheapest outcome for your situation.

Pricing and tiers change often. Confirm the current numbers on each provider’s own site before you decide; the framing above is point-in-time.

If neither quite fits, Walnut sits in a third category: chat-driven management of your own brokerage. It connects the brokerage you already use through SnapTrade, lets you analyze and manage it by talking through Claude or ChatGPT, build thematic portfolios around a thesis, and place trades you approve. Read-only by default. See Walnut vs Alpaca and Walnut vs Marcus Invest. Walnut is not an investment adviser.