ColdCard is the security-focused standard for Bitcoin-only hardware wallets. Both the Mk4 and the Q run the same open-source firmware, support the same address formats (Native SegWit bc1q and Taproot bc1p), and sign transactions in the same fundamentally air-gapped workflow. For Bitok Arena competition — generating a bc1q address, signing an outgoing transaction to the master wallet without exposing the private key to a networked device — both devices perform identically at the cryptographic level. The differences between Mk4 and Q are in the user experience of the daily workflow.
The ColdCard Q's primary additions over the Mk4 are a large backlit color display (significantly larger than the Mk4's monochrome screen), a built-in QR code scanner, and NFC for tap-to-sign interactions. For a Bitok Arena competitor who uses QR-based air-gap signing — exporting the unsigned PSBT (Partially Signed Bitcoin Transaction) as a QR code from Sparrow Wallet on a computer, scanning it with the ColdCard, signing, and exporting the signed PSBT as a QR back to Sparrow — the Q's built-in scanner makes this workflow cleaner than the Mk4, which requires either the add-on QR kit or microSD transfer.
ColdCard Mk4 and Q both generate bc1q addresses and sign Bitcoin transactions air-gapped. The Q makes the QR-based signing workflow faster and more comfortable. For daily Bitok Arena entries where air-gap is the preferred security model, the Q's integrated scanner is a genuine daily-use improvement.
Air-Gap Signing Workflow for Bitok Arena
Both ColdCard devices support three air-gap signing methods: microSD transfer (exporting PSBT to an SD card, moving the card between the ColdCard and the companion computer), QR code scanning (exporting PSBT as animated QR code from Sparrow, scanning on the ColdCard, exporting signed QR back), and NFC tap (only available on Q). For daily Bitok Arena competition entries, the QR workflow is the fastest once set up — no physical media transfer, no card removal, just scan and sign.
With the Mk4, QR scanning requires the optional ColdCard Q1 camera add-on (the Mk4 itself does not have a built-in camera) — making the QR workflow available only with the accessory purchase. The microSD workflow on Mk4 is fully functional for daily entries but adds physical handling steps. With the Q, the QR workflow is native — the built-in camera scans PSBTs directly and the display is large enough to show the signed PSBT QR clearly for Sparrow to scan back. For a daily entry workflow, the Q's integrated camera eliminates the friction point of the Mk4's external accessory.
The security model is identical between Mk4 and Q. Both use the same secure element (ATECC608B for Mk4, same manufacturer chip for Q), the same open-source firmware that can be compiled and verified independently, and the same fundamental approach to keeping private keys isolated from networked devices. The Q's additions are ergonomic — bigger screen, faster QR workflow — not security improvements. A Bitok Arena competitor who prioritizes cost over ergonomics should choose the Mk4. A competitor who uses QR-based air-gap signing daily should evaluate whether the Q's integrated camera justifies the $70 price difference in their workflow.
Companion Software for Both Devices
Both ColdCard devices work with Sparrow Wallet as the companion application for watch-only account management and PSBT creation. Sparrow handles coin control (selecting which UTXOs fund the outgoing transaction), fee rate selection, and PSBT generation — the ColdCard signs the PSBT and Sparrow broadcasts it. This workflow gives the Bitok Arena competitor full control over which address funds the entry transaction, what fee rate is applied, and what the exact destination address is — all verifiable in Sparrow before the PSBT is sent to the ColdCard for signing.
The daily workflow for either device: open Sparrow, create a new transaction to the master wallet address (verified against the current round page), set the fee rate appropriate for desired confirmation speed, export the unsigned PSBT. With Mk4: copy PSBT to microSD, insert in ColdCard, sign, copy signed PSBT back to Sparrow, broadcast. With Q: display unsigned PSBT as QR in Sparrow, scan on Q, approve signing, display signed PSBT QR on Q screen, scan back into Sparrow, broadcast. The Q's workflow requires fewer physical steps once the QR method is set up.
For a competitor making daily Bitok Arena entries over a period of months, the workflow friction of the Mk4's microSD method adds up — physical card insertion and removal is a reliable daily action, but the Q's scan-and-sign workflow is measurably faster once familiar. The decision between the two is a cost-vs-ergonomics calculation: the $70 price difference buys a faster daily workflow and a better display. For competitors who already own the Mk4, the device is fully adequate for daily competition entries — the upgrade to Q is a workflow convenience, not a capability gap.
Which One for Daily Competition
For daily Bitok Arena entry without an existing ColdCard: the Q's integrated QR scanner makes it the better choice for a QR-based air-gap workflow, and the larger display makes address verification more comfortable. For a competitor already using Mk4 and familiar with the microSD workflow: the Mk4 is fully functional for daily entries and the upgrade to Q is optional. For a competitor prioritizing minimum upfront cost with full air-gap security: the Mk4 at approximately $150 delivers the same cryptographic security as the Q at approximately $220 — the bc1q entries it produces are identical on the Bitcoin blockchain.
Both devices generate the same Native SegWit addresses, produce the same on-chain transactions, and keep private keys equally isolated from networked devices. The ColdCard's reputation in the Bitcoin self-custody community reflects the security model — both versions deliver it. The choice between them is ergonomic, not fundamental.
ColdCard Mk4 and Q both generate bc1q addresses and sign Bitok Arena entries with the same air-gap security. The Q makes the daily signing workflow faster through its built-in QR scanner and larger display. The Mk4 costs $70 less and delivers the same cryptographic outcome. Both produce transactions that the leaderboard recognizes identically.
Either device signs today's entry. The master wallet address accepts bc1q from either. Set up the workflow once, sign the transaction, broadcast from Sparrow. The leaderboard records the position the moment the transaction confirms — whichever ColdCard signed it.
Mk4 or Q — both sign the same Bitcoin transaction to the same master wallet address with the same air-gap security. The Q makes the daily QR workflow faster. The Mk4 costs less. Choose once, set up the workflow, and enter the round. The blockchain cannot tell which ColdCard signed the transaction. The leaderboard only sees the committed BTC and the address it came from.