The Blockstream Explorer API has quietly become one of the most relied-on pieces of Bitcoin infrastructure. From open-source wallets to fintech dashboards and institutional analytics tools, it underpins a growing number of production applications in both the Bitcoin and Liquid ecosystems. Now, with a series of backend improvements and new developer features, Explorer is entering its next phase as a scalable, enterprise-grade API.
Smarter Scanning with Waterfalls
One of the most important recent upgrades is the addition of Waterfalls, a new open-source scanning tool developed by Blockstream’s Riccardo Casatta. Waterfalls helps light clients scan for balances more efficiently. The real innovation is in how Waterfalls uses wallet descriptors. Instead of having the client calculate addresses locally and issue one API request per address, the client sends a descriptor once, and the server derives all the relevant addresses and history server-side. The server then returns the complete wallet history in a single structured response. This is dramatically faster than the traditional electrum-style approach, where the client calculates and queries each address separately.
A further enhancement is UTXO-only sync mode. This allows a wallet to skip its full transaction history and immediately retrieve only the unspent outputs it can spend. For large wallets with thousands of transactions, such as exchanges or custody platforms, this means they can restore balances or recover funds almost instantly. If a user just needs to know what coins are available to send right now, UTXO-only sync saves time without waiting for the full history to load.
Waterfalls is already supported in the Liquid Wallet Kit (LWK) and is being extended to Bitcoin as part of BDK. It can be self-hosted with Docker or integrated into existing infrastructure, and early benchmarks show a massive reduction in both sync time and number of requests required. For developers building web-based or mobile wallets, this is a step-change in performance and user experience.
Enabling Ark with Transaction Package Relay
Another major milestone is support for transaction package relay, introduced through the new /txs/package endpoint. This feature, requested by members of the Ark developer community, allows clients to broadcast multiple transactions together as a package rather than one by one. It solves a critical limitation of the Bitcoin mempool: low-fee parents are normally rejected, and without cooperation from cosigners you cannot replace them with higher-fee versions. By submitting both parent and child together, miners can evaluate the package holistically and confirm it using CPFP.
In addition we are updating Bitcoin Core to version to 29.1 that among other changes enables the submit package endpoint to take in a 0-fee transaction with a dust-valued anchor output, as a parent, and pay for it with a child transaction that spends the anchor output. This will bring large usability improvements to multi-party protocols like Ark where previously cooperation with a counterparty was needed to change the fee and small amounts needed to be allocated for anchor outputs.
For Ark, this is essential. Ark transactions are co-signed across many participants, and going on-chain is an emergency fallback when a counterparty disappears. In those cases, you cannot ask others to cosign a replacement. Package relay ensures these transactions remain viable, anchoring Ark’s trust-minimized design. It is the same mechanism Lightning relies on for its own fee-bumping logic, and now developers building Ark implementations can rely on Blockstream Explorer API to support it out of the box.
This integration positions Ark as one of the most exciting Layer-2 protocols in active development, and we are proud that Blockstream infrastructure is helping make it possible.
Reducing Minimum Relay Fee to 0.1
Alongside new features, we have aligned Explorer’s mempool policy with the broader Bitcoin ecosystem by reducing the minimum relay fee to 0.1sat/vB.
This may seem like a technical detail, but it has a real impact for builders and users. Bitcoin Core allows operators to set their own minimum fees, and many mempools across the ecosystem already relay transactions at 0.1sat/vB. By adopting the same policy, Explorer ensures that developers working with low-fee or experimental transactions get consistent results across environments.
It also gives wallet and protocol developers more flexibility in how they handle fees, especially during periods of low network activity when users want to minimize costs. The choice ultimately stays with miners, but lowering the relay floor makes Explorer more interoperable, predictable, and developer-friendly.
More Control with API Key Management
Teams can now issue multiple API keys under a single billing account. This unlocks better team provisioning, allows for key rotation per environment, and avoids the complexity of creating separate accounts for each developer or service. It's especially helpful for managing usage at scale and tracking who’s doing what inside your org. You still get a single billing profile, but with all the flexibility you'd expect from a serious dev environment.
Historical Usage Tracking Is Back
We’ve reintroduced historical usage views in the Explorer dashboard, giving devs and operators better visibility into how they’re consuming API calls over time. This makes it easier to optimize application performance, forecast costs, and debug traffic spikes. Combined with real-time usage insights, Explorer now offers a more complete monitoring experience that’s helpful for both product teams and ops leads.
Backend Improvements and IPv6 Support
Our infrastructure team has been working to eliminate sporadic 500 errors, improve node rotation, and generally ensure the service can support increasing load from institutional-grade clients. These fixes are ongoing, but we’re already seeing improved stability.
One notable upgrade is the addition of IPv6 support, which brings the Explorer API stack in line with modern networking standards. Previously, access was only available through IPv4. This change benefits users operating in dual-stack environments or those deploying infrastructure in IPv6-preferred regions.
Built for Every Scale
Explorer remains free for up to 500,000 requests per month. After that, usage is metered at a per-request rate, with tiers that scale up to 100 million calls and beyond. For teams that require higher throughput, low-latency performance, or isolated infrastructure, we offer enterprise deployments with custom configuration, geo-redundancy, and support for both REST and Electrum RPC.
These deployments are already powering mission-critical infrastructure. Dedicated enterprise instances are trusted by wallets and global-scale applications that need guaranteed uptime and private environments. Shared and premium tiers, meanwhile, are supporting exchanges, analytics tools, and financial dashboards at scale.
Strengthening the Open-Source Esplora and Electrs Stack
We are reinvigorating the open-source Esplora/Electrs repositories with three active maintainers focused on long-term growth. This renewed effort means faster development cycles, reliable maintenance, and deeper collaboration on industry standards. With Riccardo Casatta and the team leading contributions, Esplora continues to advance as the most robust and developer-friendly blockchain explorer backend in the Bitcoin ecosystem.
The API That Makes Bitcoin Legible
Explorer is built to make the Bitcoin network legible, usable, and production-ready. With the combination of real-time transparency, historical depth, and increasing privacy tooling, it gives builders everything they need to operate at scale. The API is actively evolving, and with new deployment options and features like Waterfalls and IPv6, it continues to grow into the backend Bitcoin deserves.
For high-volume, mission-critical use cases, Blockstream offers dedicated enterprise deployments of the Explorer API. These tailored setups provide guaranteed geo-availability across regions, single or multi-tenant options, and support for both Electrum RPC and REST endpoints, all with enhanced privacy and reliability.
To learn more, visit blockstream.info/explorer-api
For enterprise deployments, reach out to explorer-enterprise@blockstream.com