Alpaca vs Mezzi: Which Is Better in 2026?

Prices checked October 2026. A price marked (Oct 2026) was read on the vendor's own pricing page; others are described without a number because we could not verify one.

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 is a brokerage API for people building their own AI agent, best suited to developers building AI agents. On connecting an account: alpaca accounts. On execution: read + trade + paper. Cost: free (open source).

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

Aggregates your accounts and layers AI insights with a tax-aware lens. Best for a consolidated view across holdings.

How it works: Mezzi aggregates your investment accounts into one view and layers AI insights over them with a tax-aware lens, flagging things like potential wash sales, fee drag, and unrealized-gain considerations across accounts. It is read-only: it tells you what it sees and what to consider, and you act at your broker.

In practice, Mezzi’s AI aggregates accounts + tax-aware insights. It is an AI investing app that connects the brokerage you already use, best suited to aggregated wealth tracking with AI. On connecting an account: yes. On execution: read. Cost: subscription.

One honest limitation: Tracking-and-insight focused rather than thesis-driven basket building.

The core difference is category. Alpaca focuses on developers building AI agents (official MCP server (data + execution)), and Mezzi on aggregated wealth tracking with AI (aggregates accounts + tax-aware insights). On broker connection they differ too: Alpaca is “Alpaca accounts” versus Mezzi at “Yes”. 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.
• Mezzi: reads your real connected holdings. Mezzi connects your real brokerage (Yes) and works from your actual positions, so its answers reflect what you genuinely own rather than a generic model.

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.

Each one wins a different job, so the answer is committed per job rather than overall.

• Choose Alpaca if you want developers building AI agents. Its AI official MCP server (data + execution), and it costs free (open source). It is built for developers building their own automated or AI-driven trading systems. Keep in mind: developer-first; requires code and self-hosting.
• Choose Mezzi if you want aggregated wealth tracking with AI. Its AI aggregates accounts + tax-aware insights, and it costs subscription. It is built for multi-account investors who want tax-aware tracking and insights consolidated in one place. Keep in mind: tracking-and-insight focused rather than thesis-driven basket building.
• Choose Walnut if you want a keep, trim or exit read on the stocks you already own, and placing the trades you approve. It is an AI investing app that connects the broker you already use, and it costs free; Walnut Unlimited $9.99/mo on the web; no fee on assets.

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 aggregated wealth tracking with AI, and 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: free (open source). Mezzi: subscription. 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.

Prices checked October 2026. Pricing and tiers change, so confirm the current numbers on each provider’s own site before you decide.

Walnut is an AI investing app, and it is the pick for a keep, trim or exit read on the stocks you already own, and placing the trades you approve (free; Walnut Unlimited $9.99/mo on the web; no fee on assets). It connects the brokerage you already use, read-only by default, gives each holding a keep, trim or exit read against the S&P 500, flags any position above a quarter of the portfolio, and places the trades you approve. You use it through its own assistant, or inside Claude or ChatGPT. See Walnut vs Alpaca and Walnut vs Mezzi.