Your agent monitors every state. Reconciles Amazon. Prepares the return.
Then files it — while you run your store.
No spreadsheets. No quarterly scramble. No renewal shock.
Just $29/mo and a $0 penalty balance.
$29/mo founding rate · Amazon · Shopify · Walmart · No annual contract
Enterprise tax tools were priced for SAP. Others pivoted toward payment processors. The rest charge per filing across every state you operate in. None of them live inside the system that actually runs your commerce. You're left with another login, another contract, another quarterly scramble.
"The pricing we've been quoted is $7,400/year for 15,000 transactions. The fee for filing is separate. Then came the renewal — they called it a 'market adjustment.'"
"Every quarter: pull Amazon reports. Pull Shopify. Pull Walmart. Match it all in a spreadsheet nobody trusts. File. Pray. Then the notice arrives anyway."
"My FBA inventory moved to a Pennsylvania warehouse in February. I found out in August — when the notice arrived. Six months of uncollected tax."
"We moved from one tool to another. Then realized neither of them actually reconcile Amazon's marketplace-collected tax against what I still owe. I was over-remitting."
STAC isn't a dashboard you log into every quarter. It's an agent running inside Sydon Symphony — watching your channels continuously, acting when thresholds trip, and filing when deadlines approach.
Amazon FBA creates the most complex tax exposure in e-commerce — physical nexus from warehouse locations, marketplace-facilitator collected tax, settlement report reconciliation. Every major tool mentions it. None of them own it. STAC does.
Every other tool is a separate login, a separate contract, and a separate support ticket when something goes wrong. STAC is the agent that already lives inside your commerce operating system.
We tell you exactly what STAC does on day one and what's coming — not in fine print, but right here. Built from the solution architecture our engineering team uses internally.
STAC is one agent inside Sydon Symphony — the agentic commerce operating system. When your inventory agent detects an FBA shipment landing in a new state, STAC already knows before you do. That cross-agent intelligence isn't possible when your tax tool is a separate SaaS product with a separate login and a separate data model.
No “contact sales.” No demo required. The median enterprise tax software customer spends $19,143/year before filing fees. STAC’s founding rate is $348/year — published, locked, no surprises.
Sales tax compliance consumes thousands of hours and millions of dollars annually from businesses that should be spending that energy on growth. The system isn't broken — it's just never been automated properly for the sellers who need it most.
STAC exists to make the entire compliance lifecycle — monitoring, classifying, reconciling, filing — something that runs in the background without your attention. Not a tool you manage. An agent that works.
We build Sydon Symphony — an agentic operating system for commerce. STAC is the first agent in that platform: purpose-built for the tax compliance layer, designed from the ground up for Amazon-first, multi-channel operators.
We aren't a tax consulting firm that added software. We aren't a payment company that added tax. We're an AI company building the operating infrastructure that modern commerce runs on — and we started with the most painful, most neglected problem first.
8 questions. No hedging. If something's missing, the waitlist confirmation email has our direct line.
Phase 1 (July 2026 — at launch): STAC connects to your Amazon, Shopify, and Walmart accounts, monitors your nexus exposure across 45 states daily, calculates the correct rate for every transaction, classifies your products, and reconciles what Amazon collected on your behalf versus what you still owe. It produces a filing-ready summary each period — you review it and submit manually.
Phase 2 (October 2026): STAC submits returns directly to all 24 SST member states. You receive a confirmation and a timestamp. That’s it. By Phase 4, full 45-state automated filing is handled end-to-end. We show exactly which phase covers which capability — nothing is buried in fine print.
Amazon FBA creates three compliance problems that most tools handle poorly. STAC owns all three:
Traditional tax compliance tools were built for enterprise customers — global manufacturers, Fortune 500 finance teams, large ERP deployments. Their pricing, implementation requirements, and contract structures reflect that audience. The median spend on such platforms reaches $19,143/year before filing fees, and costs routinely jump 200%+ at renewal with no warning.
STAC is built for multi-channel e-commerce operators under $10M — a segment that gets systematically over-billed for capabilities it doesn’t need. We publish our price above the fold because $29/mo is the actual price, not a starting point for negotiation. The filing add-on ($39/return) is published too. There is no hidden tier, no annual lock-in, and no renewal shock.
Tax treatment varies dramatically by product and state. Protein supplements are taxable in 38 states, exempt in 7, and reduced in 2. Clothing under $110 is exempt in New York but taxable in California. These rules change multiple times a year.
STAC uses the SST Taxability Information Code (TIC) taxonomy — the industry standard covering ~300 product categories — and maps your Amazon Browse Nodes and Shopify product types to the right codes automatically. Confident classifications apply immediately. Any product STAC can’t classify with high confidence is surfaced for your one-click review, with suggested codes and the reasoning behind them.
If STAC misses a filing deadline on a return that STAC is responsible for submitting, two things happen: you don’t pay STAC for that month, and we cover the state-assessed penalty in full. No asterisks. No “subject to review.” It’s in our terms of service, not just on this page.
Coverage details: the automated filing guarantee applies from Phase 2 onward. For Phase 1, the guarantee covers calculation accuracy — if STAC’s prepared return data contains a rate or classification error that directly causes a penalty, we cover it. We carry Errors & Omissions insurance before filing goes live, because this commitment has to be backed by something real.
Yes — and you don’t need to cancel anything first. Reserve access, onboard when STAC launches in July, and run both in parallel for a quarter if you want to verify accuracy side-by-side before making the switch.
During onboarding, STAC imports your existing state registrations, maps your current filing obligations and frequencies, and picks up from where you are — not from scratch. Most operators find one quarter of parallel running is enough to be confident in the coverage.
States: Nexus monitoring, rate calculation, and product taxability across all 45 states with economic nexus thresholds, plus DC. Automated filing starts with 24 SST member states in Phase 2 (October 2026) and expands to full 45-state coverage in Phase 4.
Channels at launch: Amazon (SP-API, FBA-native), Shopify (Admin REST API), and Walmart Marketplace. QuickBooks sync and WooCommerce integrations follow in Phase 2. BigCommerce in Phase 3.
Not yet supported: Colorado home-rule jurisdictions (70+ separate returns — deferred to Phase 4), international VAT/GST, and restaurant POS integrations (Phase 4).
Sydon Symphony is the agentic operating system for commerce — a platform where individual agents (STAC for tax, and others in development for inventory, pricing, listings, forecasting, and more) share a common data layer about your business.
You do not need the full Symphony platform to use STAC. STAC works as a standalone agent with your existing Amazon, Shopify, and Walmart integrations from day one.
The advantage of being inside Symphony grows as more agents launch. STAC’s FBA nexus detection improves when it shares real-time inventory location data with the Inventory agent, for example. But that’s upside, not a prerequisite.
Founding access is limited to the first cohort. The $29/mo rate locks in permanently — it won't exist after general availability. Join the waitlist and we'll onboard you before we open to the public.
No credit card. No sales call. You'll hear from us first.