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Comparison · Comms
opus vs Stalwart
A side-by-side editorial comparison of opus and Stalwart — release velocity, themes, recent moves, and the top alternatives to consider.
opus vs Stalwart: at a glance
What is opus?
Opus put neural networks inside the codec, then pushed the sample rate to 96 kHz.
Opus is at 1.6.1, a small fix release on top of 1.6. The two releases that matter in this window are 1.5, which made the first extended use of machine learning in the encoder and decoder through Deep Redundancy and Deep PLC, and 1.6, which built on that with a wideband-to-fullband bandwidth extension module, 96 kHz support under the Opus HD name, and a 24-bit API. Between and around them sit build fixes and checksum-only patches.
What is Stalwart?
Stalwart is shipping email's next-generation auth stack while the specs are still in draft.
Stalwart is an all-in-one mail and collaboration server — SMTP, IMAP, JMAP, CalDAV, CardDAV and WebDAV in one binary — releasing every one to two weeks on the 0.16.x line. The last two months read as a standards campaign: DKIM2 and the full DMARCbis set in 0.16.12, VAPID push in 0.16.14, FreeBSD support in 0.16.13, and a run of IMAP extensions (UIDONLY, UIDBATCHES, MESSAGELIMIT/SAVELIMIT) in 0.16.17. Between the additions, most of each release is JMAP conformance repair driven by the jmap-test-suite.
opus vs Stalwart: editorial side-by-side
opus
0.0COMMS
Opus put neural networks inside the codec, then pushed the sample rate to 96 kHz.
◆ Current state
Opus is at 1.6.1, a small fix release on top of 1.6. The two releases that matter in this window are 1.5, which made the first extended use of machine learning in the encoder and decoder through Deep Redundancy and Deep PLC, and 1.6, which built on that with a wideband-to-fullband bandwidth extension module, 96 kHz support under the Opus HD name, and a 24-bit API. Between and around them sit build fixes and checksum-only patches.
◆ Where it's heading
Opus is moving in two directions that would once have looked contradictory: reconstructing audio that was never transmitted, via ML-based redundancy and loss concealment at very low bitrates, and carrying far more of it, via 96 kHz and 24-bit paths. Both extend a codec whose IETF-standard core has been frozen for years, by adding layers around it rather than changing the bitstream everyone already decodes.
◆ Prediction
With 1.6.1 confined to minor fixes and the bandwidth-extension module newly landed, the next releases are likely to tune and optimize the existing ML modules rather than add another.
Stalwart
5.0COMMS
Stalwart is shipping email's next-generation auth stack while the specs are still in draft.
◆ Current state
Stalwart is an all-in-one mail and collaboration server — SMTP, IMAP, JMAP, CalDAV, CardDAV and WebDAV in one binary — releasing every one to two weeks on the 0.16.x line. The last two months read as a standards campaign: DKIM2 and the full DMARCbis set in 0.16.12, VAPID push in 0.16.14, FreeBSD support in 0.16.13, and a run of IMAP extensions (UIDONLY, UIDBATCHES, MESSAGELIMIT/SAVELIMIT) in 0.16.17. Between the additions, most of each release is JMAP conformance repair driven by the jmap-test-suite.
◆ Where it's heading
The project is building toward being the reference implementation of the modern mail stack — JMAP first, with the classic protocols held at parity rather than left behind. The fix lists have shifted in character over these eight releases: less "feature does not work", more "spec detail is wrong", which is what a codebase looks like as it converges on conformance. Security and multi-tenancy fixes keep appearing alongside the protocol work, indicating real deployments are exercising the newer subsystems.
◆ Prediction
The next releases most likely track revisions to the drafts already implemented — DKIM2, JMAP push and the calendar drafts are all still moving — rather than adding another protocol surface. Expect continued JMAP conformance fixes until the test suite stops producing them.
Alternatives to opus and Stalwart
Other Comms products tracked by Sparkpulse, ranked by recent ship velocity. Each card links to a full editorial trajectory and lets you pivot into a head-to-head comparison with either opus or Stalwart.
Synapse
Synapse alternates release candidates with security patches on a tight two-week cycle
Canary Mail
Canary Mail ships maintenance across four platform lines; features have gone quiet since April.
Bandwidth
Bandwidth is closing the gaps that used to require a support ticket
Beeper
Beeper stopped aggregating apps and started merging the people inside them.
Respond.io
respond.io is monetizing AI usage directly while putting an assistant that builds agents in every workspace.
See all opus alternatives → · See all Stalwart alternatives →
Recent activity from opus and Stalwart
Latest ship moves from both products, interleaved chronologically. ⚡ = editorial spark.
- 1d agoStalwartIMAP gains UIDONLY, UIDBATCHES and message-limit extensions
- 9d agoStalwartJMAP delivery push arrives; strict relays stop rejecting calendar mail
- 16d agoStalwartFix-only release: JMAP semantics and a credential escalation
- 23d agoStalwartVAPID lands for JMAP Web Push
- 1mo agoStalwartFreeBSD support, plus OAuth scopes for IMAP, SMTP and Sieve
- 1mo agoStalwartDKIM2 and the full DMARCbis suite ship in one release ⚡
- 7mo agoopusOpus 1.6.1 fixes minor issues found after 1.6
- 7mo agoopusOpus 1.6 adds 96 kHz audio and ML bandwidth extension ⚡
- 1y agoopusOpus 1.5.2 fixes builds and an AVX2 crash on Windows
- 1y agoopusOpus 1.5.1 fixes the meson build
- 1y agoopusOpus 1.5 brings machine learning into the encoder and decoder ⚡
- 3y agoopusOpus 1.4 retunes in-band FEC and adds Meson support
Frequently asked questions
What is the difference between opus and Stalwart?
They serve adjacent needs but don't currently overlap on shipped themes. Stalwart is currently shipping more aggressively (velocity 5.0 vs 0.0), with 0 editorial sparks in the last 30 days against 0. See the at-a-glance table above for a side-by-side breakdown of velocity, recent sparks, and editorial themes.
Is opus better than Stalwart?
Sparkpulse doesn't pick a winner — we score release velocity, not feature parity. Stalwart is currently shipping more aggressively (velocity 5.0 vs 0.0), with 0 editorial sparks in the last 30 days against 0. For your specific use case, the alternatives sections above list other Comms products to evaluate alongside.
What are the best alternatives to opus?
Top opus alternatives in Comms are ranked by recent ship velocity. Browse the "opus alternatives" section above for the current picks, or visit /alternatives/opus-codec for the full list with editorial commentary on each.
What are the best alternatives to Stalwart?
Top Stalwart alternatives in Comms are ranked by recent ship velocity. Browse the "Stalwart alternatives" section above for the current picks, or visit /alternatives/stalwart for the full list with editorial commentary on each.