Comparison · checked 20 August 2026
VoltexAI vs Shortwave vs Spark: what BYOK actually saves you
Your AI, your key, your cost. Bring your own Anthropic or OpenAI key and you pay those APIs at their rates. Shortwave and Spark don’t offer that.
If you already have an API key, inbox AI can be bring your own key (BYOK): the model bill is yours, at list rates. Shortwave and Spark Mail only sell AI as a bundled quota inside the subscription — you cannot bring your own key. On Standard and Pro you can instead add VoltexAI Managed AI (our Anthropic key, the same pattern as the help bot) if you would rather not manage a key. That is a monthly add-on with its own action allowance, not pass-through API billing. See pricing.
How the bills actually work
| voltexai.app | Shortwave | Spark Mail | |
|---|---|---|---|
| AI billing model | Two paths: BYOK — your key, billed by OpenAI / Anthropic (or a compatible endpoint) at their rates. Or VoltexAI Managed AI on Standard and Pro — our Anthropic key, a monthly add-on. | Bundled into a per-seat subscription. Model quality and daily quota scale with the plan. | Spark +AI monthly credits on paid plans. Add-ons if you exhaust the quota. |
| Bring your own key | Yes — OpenAI, Anthropic, or OpenAI-compatible. | Not published. | Not published. |
| AI without your own key | Standard and Pro add-on: VoltexAI Managed AI (our Anthropic key). Priced as an add-on, not at Anthropic’s public API rates. | That is the only AI path — bundled into the seat. | That is the only AI path — Spark +AI credits. |
| Published AI-related price | BYOK: provider API rates. Managed AI: £3.99/mo on Standard (250 actions) or £5.99/mo on Pro (500 actions), not token pass-through. The workspace subscription is separate either way. | Individual Pro $18/seat/month. Business $30, Premier $45, Max $120/seat/month. | Plus $10/user/month ($8.25 billed annually). Pro $20/user/month ($16.58 billed annually). |
| Who picks the model | BYOK: you pick the model. Managed AI: we pick a model for that add-on. | The plan does. Free/Pro through Max map to Claude Haiku → Sonnet → Opus-class “intelligence” tiers. | Spark’s assistant, against that plan’s credit quota. |
| Mail providers | Gmail, Microsoft 365 / Outlook, iCloud, and generic IMAP — one unified inbox, plus calendar and tasks. | Gmail-first client (built as a Gmail replacement). | Multi-provider (Gmail, Outlook, iCloud, and others) across Mac, Windows, iOS, and Android. |
| Where the AI key lives | BYOK: your key, encrypted at rest; revoke it at the provider any time. Managed AI: Voltex’s Anthropic key. | Shortwave’s Claude integration on their account. | Readdle’s Spark +AI service. |
Competitor figures from each vendor’s public pricing page, checked 20 August 2026. Features and prices change; this is not a full product review.
What BYOK actually costs (a worked month)
Email AI is small prompts: a thread in, a summary or draft out. That is not a coding-agent bill. Using Anthropic’s published API rates (20 August 2026): Claude Haiku 4.5 at $1 / $5 per million input/output tokens, Claude Sonnet 5 at $2 / $10.
Assume about 2,000 input tokens and 350 output tokens per action (a typical summarise or draft). Fifty actions is a busy personal inbox; two hundred is heavy.
| Month of inbox AI | Haiku 4.5 (API) | Sonnet 5 (API) | Shortwave seat (published) | Spark +AI seat (published) |
|---|---|---|---|---|
| 50 actions | about $0.19 | about $0.38 | $18 Pro (individual) to $30–$120 on team plans — every month, whether you use 5 actions or 500. Max is how you reach Opus-class models. | $10 Plus / $20 Pro per user, plus a monthly Spark +AI credit quota. Exhaust it and you buy an add-on or wait for reset. |
| 200 actions | about $0.75 | about $1.50 |
That API column is what you pay Anthropic (or OpenAI) on a BYOK key. The seat column is what Shortwave or Spark charge for a bundled quota you cannot opt out of. VoltexAI Managed AI is closer to that second model — an add-on price, not this API maths.
Token maths: 50 × (2,000 in + 350 out). Haiku 4.5 ≈ $0.00375/action; Sonnet 5 ≈ $0.0075/action. Real threads vary. Very long threads and richer models cost more — still usually dollars, not tens of dollars, for ordinary inbox work.
Who this is for
- Developers and indie hackers who already have an OpenAI or Anthropic API key and do not want a second, bundled AI seat they cannot turn off.
- Anyone with more than one mailbox who wants one briefing across every account, not a second Gmail-only client with a $30–$120 AI seat.
- Privacy-conscious users who want to choose the provider, revoke the key, and know that BYOK mail AI only runs when their key is present.
Shortwave is a strong Gmail client if you want the inbox itself to be the AI product and you are happy to pay for that bundle. Spark is a strong cross-platform team client if you want Smart Inbox and a metered assistant included. voltexai.app is for people who want the workspace (mail, calendar, tasks) and a choice: keep AI as their infrastructure, or add VoltexAI Managed AI.
What we are not claiming
- BYOK is not “free AI”. You pay your provider. Free has a visible 25-action monthly allowance. Standard and Pro BYOK is fair use, not a metered quota. VoltexAI Managed AI is a separate add-on with its own action cap.
- VoltexAI Managed AI is not billed at Anthropic’s public API rates. It is the convenience add-on on Standard and Pro — our key, a monthly price — for people who do not want to manage BYOK.
- Shortwave and Spark include a full email client, not only AI. If you value their client more than BYOK economics, pay them for the client.
- We do not host your mailboxes. Gmail, iCloud, Outlook, or your IMAP host stays the host; we sync a working copy.
- Third-party prices above can change without notice. Check Shortwave pricing, Spark pricing, and Anthropic API pricing before you decide.
FAQ
Do you resell Claude or ChatGPT?
BYOK is not resale: you paste your own key, and billing for those model calls is between you and that provider. On Standard and Pro you can run mail AI on Voltex’s Anthropic key instead — that is the Managed AI add-on, not billed at Anthropic’s public API rates. The in-app help assistant already uses a Voltex-funded key for product questions only; it does not use your mailbox bodies.
Why do Product Hunt / Hacker News / r/selfhosted care?
Those communities already pay API invoices. A per-seat AI wrap on top of a key they already have is the thing they complain about. BYOK is the option that story wants: your key, your cost, your model choice. Managed AI is there if you would rather not run a key.
Is voltexai.app only for technical users?
No. The daily briefing, unified inbox, calendar, and tasks are for anyone. This page is the BYOK path. If you do not want to think about API keys, start at Multiple mailboxes, 1 inbox instead. Managed AI is for that audience. You can skip AI entirely; the rest of the product still works.
Keep the inbox. Bring a key — or don’t.
Create an account, connect the mailboxes you already use, and add your own AI key when you want summaries and drafts billed by your provider. On Standard and Pro, add VoltexAI Managed AI if you would rather not manage a key.
Looking at premium AI email seats instead? See VoltexAI vs Fyxer vs Superhuman.
Shortwave is a product of Shortwave. Spark Mail is a product of Readdle. Claude is a product of Anthropic. ChatGPT / OpenAI API are products of OpenAI. We are not affiliated with them. Comparison for people searching these names, checked 20 August 2026.