The question of venting is a complex one. It seems commonly (but not universally) agreed that induction units do require less venting than most other kinds, presumably because there is so little waste heat and hence hot air. Much venting advice of a general nature derives from the need to apply universally, including to the still-common gas-fueled cooking. Since gas cooking produces especially large amounts of water vapor compared to other methods, as well as toxic carbon monoxide, it requires significantly more venting capacity than any other method (including induction)—so "general" advice is likely to greatly overstate the venting needs for other forms of cooking. One cooktop maker suggests that about 2/3 the normal venting capability suffices with induction.
What is "normal" venting? Recommendations from appliance-maker trade associations—not completely unbiased sources—suggest air-movement venting capabilities of about 250 CFM (air movement in Cubic Feet per Minute) for 30-inch units (with wall-mounted hoods, not on islands), or 300 CFM for 36-inch units. Using the "two-thirds" rule of thumb, that would become, for induction, 170 CFM or 200 CFM, depending on cooktop width. One professional chef remarked that in many commercial kitchens with induction "exhaust fans can be smaller, and are frequently not installed, or left turned off entirely." Mind, building codes may (but, curiously, often do not) require some form of ventilation in a residential kitchen.
The crux, though, is what and how you cook. On one hand, a household of two adult vegetarians with a large kitchen and 10-foot ceilings in a strikingly air-tight house has never once needed ventilation turned on for stovetop cooking in ten years of using induction every day (and there are no grease deposits atop the cabinets). On the other hand, a household of several persons that does a lot of meat cooking—especially at high heat, as with frying or grilling, with their consequent grease fumes—would doubtless be an entirely different matter.
An interesting real-world study of households found that:
A sizable minority of the sample did not use their ventilation systems with any regular frequency, especially when using the oven. Noise, as the reason to avoid using the ventilation system, is not a surprising finding. Noise might explain a reluctance to use a ventilation system, especially in a busy family kitchen. However, half the sample did not even think ventilation was needed. [emphasis added]
Mind, many of those households did a lot of their "cooking" in ovens and microwaves, but still . . . .
Much depends on how simple or difficult the vent construction would be. If you are changing to induction and already have a vent system in place, you need do nothing. If you are building anew, you can usually design in whatever ducting you want or need. (Mind, those who are punctilious about energy conservation are often unhappy with exterior ducting, for a host of reasons beyond our scope here.) It is in a renovation in which you cannot—or prefer not to—use the existing venting that problems can arise, owing to structural blockages for the proposed new ducting.
If you do not regularly generate large amounts of greasy smoke, a decent alternative may be a recirculating ("ductless") hood, which passes the drawn-in air through one or more filters, usually activated charcoal, then recirculates the cleaned air back into the kitchen. That has the immense advantage that no ducting need be installed (and usually meets any code requirements). Some sources are negative on them because they do nothing about carbon monoxide or water vapor, but as we noted above, those are of concern only when gas is in use. Granted, ductless types may not suit for heavy grease-laden smoke, but they're worth considering. Look for models with high CFM and multiple filters.