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OpenAPS (oref0)

Open-source community (OpenAPS / #WeAreNotWaiting)

The original do-it-yourself closed-loop system, launched in 2015. Its oref0/oref1 reference algorithm is the open-source code that seeded the entire movement and still powers AndroidAPS and Trio. Foundational and rigorously evidenced (the CREATE randomized trial used this algorithm), but the classic rig-based OpenAPS itself is now legacy-leaning — most users run its descendants.

Available nowStrong evidenceopen-sourcediy

The scorecard

Algorithm sophistication82

The reference oref0/oref1 algorithm — prediction, autosensitivity, super-micro-bolus and unannounced-meal handling; proven in the CREATE randomized trial, though its descendants now extend it further.

Hardware support45

Tied to a narrow set of older out-of-production Medtronic pumps and a Linux 'rig'; the original Intel Edison hardware is discontinued.

Customizability96

The defining open reference design — every parameter, prediction and dosing decision is inspectable and tunable in source.

Community & docs80

Extensive ReadTheDocs documentation and a large founding #WeAreNotWaiting community, though attention has shifted to AndroidAPS and Trio.

Ease of setup25

Among the hardest to build: flashing a Linux single-board-computer rig, sourcing scarce legacy hardware, and self-maintenance via the command line.

The full picture

OpenAPS — the Open Source Artificial Pancreas System — is the project that started DIY closed-looping. After building a personal system called #DIYPS, Dana Lewis and Scott Leibrand (with Ben West, who reverse-engineered communication with older Medtronic pumps) open-sourced their work as OpenAPS in February 2015, under the community banner #WeAreNotWaiting.1 Its purpose is "an open and transparent effort to make safe and effective basic Artificial Pancreas System (APS) technology widely available" to anyone willing to build their own.2

Platform. Classic OpenAPS is not a phone app. It runs on a small Linux "rig" — historically an Intel Edison + Explorer Board, or a Raspberry Pi — that sits between your pump and continuous glucose monitor (CGM) and adjusts insulin every five minutes.1 The Edison hardware is discontinued, which is a large part of why the project is now legacy-leaning.3

Algorithm lineage and sophistication. OpenAPS publishes the reference design and the oref0 / oref1 algorithm that the whole field is built on.4 It calculates insulin-on-board, predicts where glucose is heading, and sets temporary basal rates toward a target.4 oref1 added super-micro-boluses (SMB) for faster mealtime response and unannounced-meal (UAM) handling, plus autosensitivity that adapts to changing insulin needs.4 This same code is the engine inside AndroidAPS and Trio, so OpenAPS's importance far exceeds its current direct user base.5

Supported pumps and CGMs. Direct OpenAPS works only with specific older Medtronic MiniMed pumps (e.g. 515/715, 522/722, and 554/754 Veo on early firmware), because newer firmware blocks the remote commands looping needs.6 Supported CGMs include Dexcom G4/G5/G6 and Medtronic Enlite, with other sensors usable via Nightscout.7

Customizability. Because it is the open reference implementation, every parameter and dosing decision is inspectable and tunable in source — the core promise of the movement.4

Community, docs, setup and legal status. Documentation is extensive (the OpenAPS ReadTheDocs), but building a rig is genuinely hard: flashing a single-board computer and maintaining it from the command line.1 Crucially, OpenAPS is not a regulated or commercial product — there is no company, no warranty, and the trademark is "not authorized for use by any commercial entity"; you build it and you are responsible for it.2

Clinical evidence. This is where OpenAPS is unusually strong for a DIY tool. The CREATE randomized controlled trial tested the OpenAPS 0.7.0 algorithm (inside a modified AndroidAPS) against a sensor-augmented pump in 97 children and adults; time-in-range rose from 61% to 71% with the loop versus essentially no change in controls — about 3 hours 21 minutes more per day in range — with no severe hypoglycemia or ketoacidosis.5 Its 48-week continuation confirmed a sustained ~12-point time-in-range benefit and a 0.5% HbA1c reduction.8 Observational and systematic-review data — including a pediatric survey and a systematic review of 730 participants — consistently show improved time-in-range, lower HbA1c and good quality of life, while noting most pre-RCT evidence was observational.910

What's coming. The future of this algorithm is largely its descendants: oref code lives on and evolves inside AndroidAPS and the newer Trio, where active development now concentrates.53 OpenAPS itself remains available and its reference design is still maintained as the canonical specification, but new users are generally steered toward those app-based successors rather than building a classic rig.3

References

  1. OpenAPS. Project History — DIYPS, founding by Dana Lewis, Scott Leibrand and Ben West, and the February 2015 open-source launch. OpenAPS ReadTheDocs (accessed 2026). https://openaps.readthedocs.io/en/latest/docs/Resources/history.html ↩ ↩2 ↩3

  2. OpenAPS. What is #OpenAPS? — mission statement, self-build/self-responsibility, and non-commercial trademark. OpenAPS.org (accessed 2026). https://openaps.org/what-is-openaps/ ↩ ↩2

  3. openaps/oref0 — releases and commit history (stable oref0 0.7.0, 10 Nov 2019; ongoing reference maintenance). GitHub (accessed 2026). https://github.com/openaps/oref0/releases ↩ ↩2 ↩3

  4. OpenAPS. OpenAPS Reference Design — oref0/oref1 algorithm, IOB, prediction, temp-basal dosing, SMB, UAM and autosensitivity. OpenAPS.org (accessed 2026). https://openaps.org/reference-design/ ↩ ↩2 ↩3 ↩4

  5. Burnside MJ, Lewis DM, Crocket HR, et al. Open-Source Automated Insulin Delivery in Type 1 Diabetes (CREATE trial; OpenAPS 0.7.0 algorithm). N Engl J Med 387:869-881 (2022). doi:10.1056/NEJMoa2203913. https://pubmed.ncbi.nlm.nih.gov/36069869/ ↩ ↩2 ↩3

  6. OpenAPS. Compatible insulin pumps (older Medtronic models and firmware limits). OpenAPS ReadTheDocs (accessed 2026). https://openaps.readthedocs.io/en/latest/docs/Gear%20Up/pump.html ↩

  7. OpenAPS. Information about compatible CGMs (Dexcom G4/G5/G6, Medtronic Enlite, Nightscout). OpenAPS ReadTheDocs (accessed 2026). https://openaps.readthedocs.io/en/latest/docs/Gear%20Up/CGM.html ↩

  8. Burnside MJ, Lewis DM, Crocket HR, et al. Extended Use of an Open-Source Automated Insulin Delivery System: 24-Week Continuation Phase Following the CREATE RCT. Diabetes Technol Ther 25:250-259 (2023). doi:10.1089/dia.2022.0484. https://pubmed.ncbi.nlm.nih.gov/36763345/ ↩

  9. Braune K, O'Donnell S, Cleal B, et al. Real-World Use of Do-It-Yourself Artificial Pancreas Systems in Children and Adolescents With Type 1 Diabetes: Online Survey and Self-Reported Outcomes. JMIR Mhealth Uhealth 7:e14087 (2019). doi:10.2196/14087. https://pubmed.ncbi.nlm.nih.gov/31364599/ ↩

  10. Asarani NAM, Reynolds AN, Elbalshy M, et al. Efficacy, safety, and user experience of DIY or open-source artificial pancreas systems: a systematic review (730 participants). Acta Diabetol 58:539-547 (2021). doi:10.1007/s00592-020-01623-4. https://pubmed.ncbi.nlm.nih.gov/33128136/ ↩