AID Systems Guide — Control-IQ
Tandem t:slim X2 with Control-IQ
Control-IQ is one of the most customisable mainstream AID systems. Understanding which levers to pull — and why — is what tends to make the difference between it feeling brilliant or frustrating.
System profile
Pivotal trial: Breton MD et al. (2020). Randomized trial of closed-loop control in children with type 1 diabetes. N Engl J Med. 383:836-845.
About this system
Control-IQ is sometimes described as the Spider-Man of AID systems: “With great power comes great responsibility.” It rewards understanding.
Want to listen to the podcast? Episode 2: Mastering Control-IQ – The Spider-Man of AID explores why this system can work brilliantly when settings are close, behaviour matches the system, and the user understands which levers matter most.
What makes Control-IQ different
- It is one of the most customisable mainstream AID systems
- User settings still strongly shape how the algorithm behaves
- It can be tuned to feel more or less responsive
- That flexibility is useful — but it also means poor settings are felt more quickly
What this guide covers
- How the algorithm actually works
- Which settings matter most
- Which lever to pull when it feels too aggressive or not responsive enough
- How age, activity, and behaviour change the ideal setup
- How the Explorer helps you understand direction of change without copying settings blindly
How the algorithm works
The t:slim X2 with Control-IQ has three parts:
- The t:slim X2 pump
- A compatible sensor — Dexcom G6, Dexcom G7, or Libre 2 Plus depending on region
- The Control-IQ algorithm inside the pump
Control-IQ is powerful because it does more than suspend insulin. It can reduce basal, increase basal, and give automated correction boluses.
Control-IQ in plain English
- The algorithm works from your programmed settings — especially your basal profile and correction factor
- It predicts where glucose is heading and adjusts insulin before glucose actually gets there
- It can reduce or suspend insulin if glucose is predicted to go low
- It can increase basal insulin when glucose is rising
- It can give an automated correction bolus when glucose is predicted high
- It uses a fixed 5-hour insulin action model, so it tends to remain cautious and can feel slower than some people expect after meals or missed boluses
The key point: Control-IQ is not a fully independent pancreas. It is a powerful system built on your settings. The better those settings reflect real physiology, the better the algorithm tends to behave.
Why it can feel brilliant or frustrating
- If settings are close, it tends to feel smart, smooth, and effective
- If correction factor is too weak, it can feel sleepy and underpowered
- If basal is too low, it has less room to work
- If meal boluses are too dominant, the system can feel less flexible and exercise becomes harder
- If behaviour is mismatched — especially missed meal boluses — the algorithm is being asked to rescue a problem it was not designed to solve
How to optimise Control-IQ
Control-IQ is one of the few AID systems where the user can meaningfully shape responsiveness. That is a strength — but only if you understand which lever you are pulling.
The main levers
Correction factor
Most important lever for responsiveness. A stronger correction factor tends to make Control-IQ more responsive. A weaker correction factor tends to make it more cautious.
Basal profile
Sets the platform the algorithm works from. If basal is too low, Control-IQ has less room to increase. If basal is too high, low risk rises and the system tends to spend more time pulling back.
Carbohydrate ratio
Changes how much work is done by the meal bolus versus the algorithm. Slightly weaker carbohydrate ratios can shift more work toward automated basal and auto corrections.
Behaviour
Still matters a lot. Missed boluses, late boluses, grazing, high-fat meals, and exercise all change how the same settings feel in real life.
A practical pattern that often works well
- Basal around 50–60% of total daily insulin
- Slightly weaker carbohydrate ratios
- Strong correction factors
This often gives the algorithm more room to help while keeping meal insulin from doing all the work up front. Individual results vary — this is a starting direction, not a universal prescription.
Which lever to pull
- If Control-IQ feels too slow: correction factor is usually the first thing worth reviewing
- If it is always increasing basal but still not coping: the basal profile may be worth reviewing
- If there are consistent lows after eating: carbohydrate ratio may be worth reviewing
- If highs are driven by missed carb entries or delayed boluses: behaviour often needs addressing before settings
Avoid changing everything at once. The most useful question to start with is: what problem am I actually trying to solve?
Know which lever you are pulling
A common experience is that a system feels too aggressive or not aggressive enough. That framing is too broad to be useful. The more productive question is: which part feels wrong?
If the system tends to feel too aggressive
- Lows after exercise or active days — basal and total insulin exposure may be too high for that context
- Lows after the system has been helping with highs — correction factor may be too strong
- Lows after meals — carbohydrate ratio may be too strong, or pre-bolus timing may be too long
If the system tends to feel not responsive enough
- Long periods high after meals — meal timing, meal dose, or carbohydrate counting may be the main issue
- Glucose drifting high between meals and overnight — basal may be too low
- The algorithm not pulling highs down well — correction factor may be too weak
Control-IQ is best understood as a system you can steer. It is not about random adjustment. It is about understanding whether to change basal, correction factor, carbohydrate ratio, or behaviour.
The GNL 5-level framework
Control-IQ responsiveness is characterised by three primary levers in a strict order of clinical impact, with sleep mode sitting alongside as an additional consideration rather than a level axis. This is the hierarchy the GNL AID System Explorer uses, locked with Laurel Messer (Tandem VP Medical Affairs) on 16 April 2026.
| Level | Label | 1. CF rule (mmol/L) | 1. CF rule (mg/dL) | 2. Basal % (calculation) | 3. ICR rule (g / u) |
|---|---|---|---|---|---|
| 5 | Optimal | 80 / TDD | 1400 / TDD | 65% | 300 / TDD |
| 4 | High | 85 / TDD | 1500 / TDD | 60% | 330 / TDD |
| 3 | Balanced (default start for most adults) | 90 / TDD | 1600 / TDD | 55% | 400 / TDD |
| 2 | Gentle | 100 / TDD | 1800 / TDD | 50% | 450 / TDD |
| 1 | Protective | 110 / TDD | 2000 / TDD | 45% | 500 / TDD |
Third lever is ICR, not “Bolus %”. The framework was updated on 17 April 2026 after review with Laurel Messer (Tandem Global Medical Affairs). “Bolus %” is not a pump setting and is not actionable; ICR is the real user-delivered lever and maps cleanly to ISPAD 2024 Chapter 23 paediatric guidance.
How to use the framework in practice
Start at Level 3 for most adults with T1D. Children (especially preschoolers) often need a stronger ICR rule from the outset per ISPAD 2024 Chapter 23 (the 330 or 250 rule; breakfast ICR may need 150/TDD). Start paediatric patients at Level 4 or Level 5 on ICR while keeping CF at the Balanced setting, then progress.
Most people are moved up to Level 4, then Level 5, as fast as the person tolerates. The stop condition is time below range (glucose below 3.9 mmol/L) rising above 4%. If time below range goes above 4%, hold at the current level or step back one.
Use the t:slim X2 profile feature. One of the advantages of Control-IQ is that several user profiles can be pre-loaded on the pump. The recommended set is Levels 2, 3, 4 and 5, loaded in advance. Level 1 is extremely unlikely to be appropriate in practice and is only pre-loaded if a specific clinical reason exists. The user starts in Level 3 and steps up through Level 4 and Level 5 as time below range allows.
Sleep Activity, an additional consideration, not a level. Sleep Activity tightens the target, makes the every-5-minute insulin delivery more aggressive, and disables the Autobolus while active.
- Run Sleep Activity 24 hours a day, every day when the person gives most of their boluses for meals. The 5-minute delivery tightens; the Autobolus is not needed because meal coverage is handled by the user.
- Run Sleep Activity at night only when daytime boluses are regularly missed. This keeps the daytime Autobolus active to cover meal excursions the user has not bolused for.
- Do not run Sleep Activity 24/7 if boluses are being missed. Removing the daytime Autobolus safety net typically leads to more hyperglycaemia, not hypoglycaemia.
Explore how settings change Control-IQ behaviour
The T:slim Explorer is not there to hand out perfect settings. It is there to show how different settings change algorithm responsiveness, insulin exposure, and likely real-world behaviour.
The real value of the Explorer:
- It shows why the same glucose can mean different things depending on active insulin exposure
- It makes visible how correction factor changes algorithm intensity
- It shows why basal gives the system room to work
- It helps explain why the fixed 5-hour insulin model matters for exercise and hypos
- It shows why average best settings fit the middle of the distribution, not everyone equally
- It helps people and clinicians discuss direction of change rather than copying settings blindly
Use the Explorer to understand direction, trade-offs, and likely behaviour. It is an education and discussion tool — not a shortcut to copied settings.
Different people need different starting positions
There is no single perfect Control-IQ setup for everyone. The ideal starting point tends to depend on physiology, behaviour, activity, and the cost of being wrong.
Young children
A more balanced starting position tends to be appropriate. Intake and activity are less predictable, insulin sensitivity is high, and unexpected lows carry higher cost.
Adolescents with missed boluses
A more responsive setup may help, because the system is often being asked to compensate for delayed or missed insulin.
Highly active people
A more cautious or more flexible setup often works better. The interaction between insulin exposure and activity matters significantly.
Older adults or those where hypos carry high risk
Bias toward safety. Avoid chasing perfection if the downside of hypos is large.
A useful principle: choose the setup that matches the real-life pattern, not the theoretical ideal.
Sleep mode, exercise, and insulin exposure
Control-IQ tends to be easier to understand once you accept one important principle: the pump can reduce future insulin, but it cannot remove insulin that is already in the body.
- Sleep Activity sits outside the 5-level framework as an additional consideration. It tightens the target, makes the every-5-minute delivery more aggressive, and disables the Autobolus while active. Run it 24/7 if the person boluses regularly for meals; run it at night only if daytime meal boluses are regularly missed, so the daytime Autobolus stays active. Running Sleep Activity 24/7 without regular bolusing typically leads to more hyperglycaemia, not hypoglycaemia (the Autobolus safety net is removed). Sleep Activity does not solve poor meal behaviour or high insulin exposure from earlier in the day
- Exercise problems are often not purely exercise problems, they are insulin exposure problems made visible by activity
- The fixed 5-hour action model is useful for exercise awareness because it gives a rough picture of ongoing physiological exposure
A useful exercise principle
When active insulin exposure is still high, activity is more likely to produce a hypo. When exposure is modest and glucose is elevated, activity can sometimes help bring it down. This is why two people can start exercise at the same glucose and have very different outcomes — the missing variable is often insulin exposure.
Foundations that still matter
Strong time in range on Control-IQ tends to come from combining the algorithm with good underlying habits. The algorithm is powerful — it is not magic.
- Three balanced meals
- Accurate carbohydrate counting
- Bolus insulin 10–20 minutes before eating when appropriate
- Understanding what activity does to glucose and insulin exposure
- Rotating sites and resolving infusion issues early
Best optimisation approach: understand the problem before changing anything.
Work out whether the issue is basal, correction factor, carbohydrate ratio, meal timing, missed boluses, or exercise. Then change the thing that actually matches the problem — not everything at once.
Starting settings are only a starting point
Average best settings are useful for orientation. They are not a promise of a perfect individual result. In real life, the “best average” settings tend to fit the middle of the distribution. Many people land somewhere in that zone, but not exactly on it.
That is why the Explorer is useful — it helps you understand direction of change and gives a framework for discussion with your care team.
A useful two-phase approach
- Survive: get safe, stable, and familiar first
- Thrive: then optimise once you understand the patterns
Download the How to Survive and Thrive Guide — t:slim X2 summary. A full workbook is also available: t:slim X2 Workbook.
This content is for educational exploration only. It describes average responses and general principles. It is not medical advice and cannot replace individual clinical guidance from your diabetes care team.
Control-IQ+, the Tandem Mobi, and the CGM options (launching 18 May 2026 in the UK)
Control-IQ+ (CIQ+) is the next-generation Tandem algorithm. It launches in the US on 17 May 2026 and in the UK on 18 May 2026. It is helpful to separate what is changing into three product stories that often get conflated: the algorithm, the pump, and the compatible CGMs. Each has its own timeline and market availability.
1. The algorithm, Control-IQ+
CIQ+ brings four real changes on top of current Control-IQ. Weight range 9 to 200 kg (was 25 to 140); the 9 kg floor is what enables the age 2+ indication. Total daily insulin range 5 to 200 units/day (was 10 to 100). Temp basal is now available while automation is ON (up to 72 hours); previously you had to switch automation off. Extended bolus is now available while automation is ON (up to 8 hours). Autobolus is unchanged: it has always been system-initiated with no user confirmation, and CIQ+ retains identical Autobolus behaviour.
2. The pump, Tandem Mobi
Mobi is a small on-body pump, worn via an adhesive sleeve or clipped to clothing, connected to the infusion site by a short 12 cm infusion line. It is not tubeless in the Omnipod sense; the wear experience is patch-like but there is still a short infusion line. Mobi runs CIQ+ only, not current Control-IQ. The t:slim X2 continues as the full-size pump option running CIQ+. Regional availability is limited at launch. Tandem product page.
3. The compatible CGMs (market-specific)
CGM compatibility differs by market. UK: current Control-IQ is Dexcom G6 or G7; CIQ+ adds FreeStyle Libre 3 Plus on 18 May 2026, the first Tandem-Libre integration in the UK. US: current Control-IQ has integrated with Libre 2 Plus since January 2024; CIQ+ upgrades this line to Libre 3 Plus on 17 May 2026. International rollout continues through 2026.
What to be careful about. CIQ+ and current Control-IQ are different algorithm versions. Tandem Mobi is only available with CIQ+, not current Control-IQ. Autobolus behaviour is the same in both versions, do not expect a step-change in correction behaviour at the algorithm switch.