What is the actual difference between an AGS cut grade and a GIA cut grade?

GIA grades the diamond's proportions — table, crown angle, pavilion angle, polish, symmetry — and assigns one of five categorical tiers (Excellent / Very Good / Good / Fair / Poor) based on whether those measurements fall inside the reference bucket. AGS measured the actual light coming back out of the stone, using ray-traced simulation against a 3D scan plus ASET imaging, and assigned a continuous 0-to-10 numeric grade with 0 the top of the scale. Two rounds that both print GIA Excellent can land at AGS 0 and AGS 2, because the GIA proportion bucket is wider than the AGS light-performance step. GIA grades what the stone is built like; AGS measured what the stone actually does with light.

Is AGS still grading diamonds in 2026?

AGS Laboratories closed standalone grading operations in late 2022. The Las Vegas grading facility, the AGS Performance Grading Standard intellectual property, the ASET methodology, the ray-tracing software, and the research staff transferred to GIA under an acquisition agreement. The science was not retired — it now ships as the AGS Ideal Report digital supplement, available on qualifying GIA Diamond Grading Reports and GIA Laboratory-Grown Diamond Reports for roughly $25 per stone. The American Gem Society itself, the non-profit trade association, continues to operate separately from the closed lab.

Is an AGS Ideal supplement worth the extra $25 on top of a GIA report?

On a round natural between roughly $4,000 and $15,000, yes — the AGS 0 verdict isolates a top 10–15% of GIA Triple Excellent stones, and informed trade resale buyers pay a 3–7% premium for the verified supplement. On a round natural above $15,000, yes, and read the ASET image alongside the grade. On any round marketed as "super ideal" or "true hearts and arrows", yes — the supplement is what verifies the marketing copy. On a lab-grown round in 2026, yes — since GIA dropped granular 4Cs from its lab-grown report in October 2025, the AGS Ideal supplement is the most defensible independent light-performance credential left on the document. On a round natural under roughly $4,000 a clean GIA Triple Excellent is enough.

Does AGS issue cut grades on fancy shapes?

Yes — AGS Laboratories was the only major lab to publish a measured overall cut grade on princess, emerald, oval, cushion, radiant, and (after 2018) Asscher cuts, and the AGS Ideal Report supplement inside GIA covers a subset of those fancy shapes today. GIA still does not print an overall cut grade on fancy shapes; the GIA report lists polish, symmetry, and proportion measurements but stops short of a verdict. For a fancy-shape buyer who wants an independent cut credential, the AGS Ideal supplement is the only one available.

Is a pre-2022 AGS Platinum report still a valid document?

Yes. The AGS Platinum Light Performance report issued before the late-2022 closure is a valid grading document and the AGS 0 verdict still means what it meant when issued. To informed trade buyers the paper carries full parity with GIA, because the same Performance Grading Standard and the same ray-tracing software transferred to GIA in the acquisition. To general-retail buyers post-closure the paper typically absorbs a 5–10% paper-unfamiliarity discount — which is exactly when sellers commonly pull a fresh GIA report and add the AGS Ideal supplement to recover full price parity.

AGS vs GIA: Cut Grade Methodology & Lab History — Side-by-Side Reference (2026)

Lab history in five lines

1931 / 1934. GIA founded (1931) and AGS founded (1934) by the same gemologist, Robert M. Shipley. GIA built the grading scales the trade still uses; AGS ran the retailer-ethics association.
1996. AGS opens AGS Laboratories in Nevada — a dedicated diamond lab whose brief was an explicitly measured cut grade based on light performance, not proportion buckets.
Mid-2000s to 2010s. AGS extends the Performance Grading Standard from rounds to qualifying fancy shapes (princess, emerald, oval, cushion, radiant, then Asscher). GIA introduces its own cut grade for rounds only in January 2006, ten years after AGS opened.
Late 2022. AGS Laboratories closes standalone grading. The Las Vegas facility, the Performance Grading Standard IP, the ASET methodology, the ray-tracing software, and the research staff transfer to GIA.
2023–2026. GIA launches the AGS Ideal Report supplement (~$25 per stone) on qualifying GIA reports. The science continues inside GIA; the standalone Platinum paper is a legacy document on the secondary market.

Methodology side-by-side

Dimension	GIA	AGS (pre-2022) / AGS Ideal supplement (2023+)
Cut grade scale	Excellent / Very Good / Good / Fair / Poor — categorical, 5 tiers	0 (Ideal) → 10 (Poor), continuous numeric in 0.5 increments
What is graded	Proportions (table, crown angle, pavilion angle), polish, symmetry, observer-panel face-up appearance	Ray-traced light output: brightness, contrast, dispersion (fire), leakage — each graded on the 0–10 scale
Visual evidence on report	Proportion diagram + hand-drawn clarity plot (full report)	Proportion diagram + clarity plot (legacy Platinum) plus ASET image with four-colour light-zone map
Fancy-shape cut grade	No overall grade — measurements only	Yes — princess, emerald, oval, cushion, radiant, Asscher
Fluorescence	None / Faint / Medium / Strong / Very Strong + colour	None / Faint / Medium / Strong / Very Strong + colour — same scale, interchangeable
Colored stones	Grading + country-of-origin opinion on selected stones	Diamonds only — no colored-stone reporting ever
Lab status (2026)	Active	Standalone lab closed late 2022; methodology lives on as the AGS Ideal Report supplement inside GIA (~$25 per stone)
Trade shorthand	"Triple Ex" = Excellent cut, polish, symmetry	"AGS 0" or "AGS 000" = top tier across light performance, proportion, polish, and symmetry

Report anatomy: line-by-line differences

Cut grade vocabulary. GIA prints one of five English-language tiers. AGS prints a number. There is no clean one-to-one map — a GIA Triple Excellent may sit at AGS 0, AGS 1, or AGS 2 depending on what the ray-tracer reports.
Light-performance statement. The AGS report and the AGS Ideal supplement print an ASET image alongside the numeric grade. GIA reports do not include an ASET image; the cut grade is the entire light-performance statement on the GIA report unless the AGS Ideal supplement is attached.
Clarity plot. Full GIA Diamond Grading Reports and pre-2022 AGS Platinum reports both carry a hand-drawn inclusion plot with the same red-for-inclusions and green-for-surface conventions. GIA Dossiers (the abbreviated report for smaller stones) omit the plot; AGS Platinum carried one regardless of size.
Origin opinions. If the stone is colored (sapphire, ruby, emerald, Paraiba), only GIA prints a country opinion. An "AGS" report on a colored stone is misidentified or fabricated — AGS Laboratories was a diamond lab.

Four-line buyer verdict by spend band

Round natural under ~$4,000. GIA Triple Excellent is enough. Skip the AGS Ideal supplement — the $25 cost and the trade premium it earns are out of proportion to the spend at this size.
Round natural $4,000 – $15,000. Add the AGS Ideal supplement. The cut premium is meaningful relative to the ticket and the AGS 0 verdict isolates a visibly better-performing stone under the spot lighting most engagement rings actually live under.
Any round above $15,000 or marketed as "super ideal". Add the supplement and read the ASET image, not just the grade. At this spend the gap between AGS 0 and AGS 1 is real money, and the image is what verifies the marketing copy.
Lab-grown round in 2026, or any fancy shape. Add the supplement — since GIA dropped granular 4Cs from the lab-grown report in October 2025 and prints no overall cut grade on fancy shapes, the AGS Ideal supplement is the only independent cut credential left on the document.

The one-line summary

GIA Excellent is a proportion bucket; AGS 0 is a measured light-performance verdict; in 2026 you can get both on a single GIA + AGS Ideal report for about $25 extra. The 2022 closure of AGS Laboratories changed which paper you can get standalone, not which grading philosophy the trade still respects.

Read alongside

AGS vs GIA authority hub — the long-form companion to this reference, with the full ASET methodology end to end, the 2022 acquisition timeline, the post-merger trade acceptance picture, and the resale-impact dollar bands.
AGS cut grade chart — every number 0 through 10 with its GIA cut-grade equivalent on a single page.
How to read a GIA report — line-by-line walkthrough of the document the AGS Ideal supplement attaches to.
AGS cut grade history and legacy reports — deep editorial on AGS Laboratories from the 1996 launch through the 2022 closure, with a read of pre-2022 AGS Platinum paper.
GIA vs IGI vs AGS — the three-lab decision that adds IGI to the picture.
Diamond and gemstone lexicon — anchor-linked glossary covering ASET, AGS Performance Grading Standard, Triple Excellent, and the rest of the grading vocabulary used here.