It will mean changes to the way calls are prioritised to concentrate on "immediately life-threatening" cases such as cardiac arrest.
The ambulance service has struggled to meet its target to respond to 75% of category A calls within eight minutes.
Under the new system, some call-outs, including certain types of chest pains or head injuries, will be downgraded.
This will give ambulance crews longer to attend.
The ambulance service said current figures showed they managed to get to 67.5% of Category A calls within 8 minutes.
They said the changes would mean highly-trained call handlers targeting the right response for each patient.
The new system will start at the end of this year and be reviewed after a year.
Patients with immediately life-threatening conditions, such as cardiac arrest, or who have been involved in serious road traffic incidents, will be prioritised and receive the fastest response.
In less urgent cases, call handlers may spend more time with patients to better understand their health needs and ensure they send the most appropriate resource for their condition.
The move follows similar changes in Wales and parts of England which have proved to be highly successful - leading to faster response times for critically-ill patients.
The Scottish Ambulance Service said the new response model had been developed following the most extensive clinically-evidenced review of its type ever undertaken in the UK - with nearly half a million calls examined.
It is the first major change to the time-based targets system since 1974.
Pauline Howie, the service's chief executive, said: "The new model will allow us to respond faster to more patients with time-critical, immediately life-threatening conditions. In other situations, we will safely and more effectively identify and send the right resource first time for patients, resulting in better overall clinical outcomes.
"The focus on time-based targets for ambulance responses has changed little in around 40 years and does not take account of the advances made in clinical development of pre-hospital care."
Scotland's Chief Medical Officer, Dr Catherine Calderwood, said: "The Scottish Ambulance Service has undertaken a rigorous review of its clinical data, involving a full year of actual patient outcome data being analysed.
"What the analysis showed was that the current coding system does not always accurately identify some patients' conditions as immediately life-threatening. And that other codes were getting an eight-minute response, although the patient's condition had no time-critical response requirement.
"I am persuaded by the extensive clinical evidence that the Scottish Ambulance Service has put forward and know that patient safety is at the heart of these changes."
She added: "We will keep this pilot under close review over the next 12 months to ensure that we are seeing the improvements to patient safety and patient outcomes that are expected."
Dr Mike Knapton, associate medical director at the British Heart Foundation, said: "I am pleased that this new clinical response model is based on evidence, unlike the eight-minute standard response time which was a pragmatic target set in 1974.
"The quality of patient care, before a person even reaches hospital, has improved dramatically over the years and we understand that today's operational practices should evolve to reflect that.
"In the event of a cardiac arrest, time is critical and the best way to get professional help is to call 999 without delay. I'll look forward to seeing the results of this pilot to ensure that heart patients continue to receive timely and quality care."
Scottish Conservative health spokesman Donald Cameron said: "Anything that can improve response times should be considered, and this is a welcome pilot.
"The ambulance service has had problems with response times over the years, and it's right that it seeks to change this.
"However, the organisation will have work to do if it's to persuade people this is the correct approach.
"Some will wonder if those in urgent need of an ambulance, but haven't suffered a heart attack or been in a road accident, risk receiving a lesser service."
Scottish Liberal Democrat health spokesman Alex Cole-Hamilton said: "If this move by the Scottish Ambulance Service makes the system more intelligent and improves the care that patients receive then it is very much welcome.
"However, last month we revealed that over 4,000 of the most urgent call outs took longer than 20 minutes for an ambulance to arrive. While this change may improve the system, it cannot be a substitution for ensuring ministers give the support the service needs."
A new response system for 999 calls is to be piloted by the Scottish Ambulance Service.