Technological Achievement Tiers
A Technological Achievement Tier was a level of categorization used by the Forerunners to assess the technological advancement of civilizations. This system was later adopted by the Covenant. There are a total of seven tiers, and the lower the Tier number, the more advanced the civilization's technology is/was.
Tier 7: Pre-Industrial
Tier 7 is one of the most common and stable states, with limited weaponry and environmental threats. Societies tend to be small and scattered, driven by subsistence farming, foraging, or hunter-gathering needs. Technology is limited to simple hand made tools, weapons, or agrarian implements and methods, but a very broad understanding of planetary and solar mechanics is not uncommon.
Every race indexed in the Conservation Measure was placed at this level after reseeding.. The Flood is natively at this Tier level, but can jump up to any tier depending on the intelligence of the host whom they infect.
Tier 6: Industrial
Tier 6 is the outset for massive urbanization. Agrarian societies can remain stable in the pre-industrial stage, but Tier 6 population strain and mechanized food production invariably create political and economic pressures very few can balance. Moving past this usually promises advancement. Some societies improve environmental and medical understanding concurrently with mechanical and transport advancement. Those that do not are frequently doomed.
Humanity stood on this level from the late 18th to the mid-20th century. This level is also where the Unggoy were before joining the Covenant. It is possible that the Jiralhanae stood in this level before joining the Covenant, because they had recently rediscovered the radio and flight before they were found by the Covenant.
Tier 5: Atomic Age
Tier 5 species usually begin focusing on clean energy production. The occasional belligerent species will use atomic energy for weapons, often resulting in mass extinctions. In-atmosphere craft are a hallmark, often leading to manned space flight, albeit in a short-scale.
Tier 4: Space Age
Tier 4 is often the final resting place for species intelligent enough to break free from their cradle's surface only to fill the gulf surrounding it with war. Their comfort-focused technology can include medical advances.
This is the tier where humanity stood at the time of the Interplanetary War in the 2160s, having met the conditions with the development of viable space travel during the 21st century. This level is also where the Kig-Yar and Yanme'e were before joining the Covenant. In some period of their history the Jiralhanae reached this level, but because of a bloody war between rival master-packs, their civilization fell back to the pre-industrial age.
Tier 3: Space-Faring
Species has efficient slipspace navigation, mass drivers, asynchronous linear-induction weapons, holocrystal storage and semi-sentient AI—though their creation requires memory transfer from the freshly deceased and/or flash cloning. They have had no outside influence.
Tier 2: Interstellar
The species has the ability to perform exceedingly accurate slipspace navigation, near-instantaneous interstellar communication and man-portable application of energy manipulation. The unified state of the 26th-century Covenant stood at this level.
Both San'Shyuum of the Covenant and Sangheili brought the other races of the Covenant to such a high technological level when incorporating them into the Covenant. The two primary extant interstellar civilizations were space-faring prior to discovering Forerunner artifacts—or each other—but they have not successfully reverse-engineered those artifacts.
Tier 1: World Builders
The species has the ability to manipulate gravitational forces, create AI with full sentience, fabricate super-dense materials, perform super-accurate slipspace navigation, the ability to create life, and the ability to create worlds. The Forerunners are the most prominent civilization to have reached this level. Given their technological sophistication, it is possible that prehistoric San'Shyuum and prehistoric humans also stood at Tier 1 before their defeat by the Forerunners.
Tier 0: Transsentient
As the Forerunners had no examples of civilizations with technological accomplishments greater than themselves—with the exception of the Precursors—this is a theoretical ceiling. It is suspected that they can travel across galaxies and accelerate the evolution of intelligent life.
The state of transsentience is evidently connected less to the level of available technology as understood in the traditional sense and more to a metaphysical elevation of the beings themselves beyond conventional existence. The Precursors' technology was created through neural physics; an abstract interplay between thought and the fabric of reality. The Flood's compound mind may also be understood as a form of transsentient being; indeed, in the later stages of the Forerunner-Flood war, the Flood was able to tap into neural physics and control Precursor artifacts.
The technological achievement scale is similar to the real-world Kardashev scale, which measures technological advancement based upon the total amount of energy a civilization is capable of harnessing. Similar categorical scales are commonly found in science fiction.