Why We Need a Metric
The collapse of Stack Overflow and Chegg aren't isolated incidents. They're manifestations of a systematic force — horizontal gravity — that's restructuring digital markets at the category level. But without a quantitative framework, we're left with anecdotes.
The Horizontal Gravity Index (HGI) changes that. It's a composite metric designed to track the pace and magnitude of lateral capability absorption across industries.
The Formula
HGI(t) = α·S(t) + β·A(t) + γ·V(t)
Three independently measurable sub-indices:
- S(t) — SaaS Consolidation Rate: Normalized decline in distinct SaaS applications per organization. Data source: Productiv SaaS Management Index.
- A(t) — API Integration Density: Cross-application API call volume normalized to baseline. Data source: Postman State of APIs reports.
- V(t) — Vertical Market Cap Decline: Aggregate market cap loss in pure-play vertical software companies. Data source: Public equity markets.
The weights α, β, γ are normalized such that α + β + γ = 1. The baseline uses equal weighting (⅓ each), with domain-specific calibrations available when one channel dominates.
Three Phases
The HGI maps to three distinct market phases:
| Phase | HGI Range | Description |
|---|---|---|
| Emerging | < 0.3 | AI capabilities present but not yet disrupting core vertical value propositions |
| Accelerating | 0.3 – 0.7 | Active market share transfer from vertical specialists to horizontal platforms |
| Critical Absorption | > 0.7 | Vertical category boundaries effectively dissolved; standalone viability questionable |
Where Each Industry Stands (2026)
| Industry | HGI | Phase |
|---|---|---|
| Developer Tools | 0.67 | Accelerating |
| Education Technology | 0.58 | Accelerating |
| Enterprise SaaS | 0.48 | Accelerating |
| Financial Services | 0.32 | Accelerating |
| Legal Technology | 0.28 | Emerging |
| Healthcare IT | 0.15 | Emerging |
Developer tools lead the curve — unsurprising given that LLMs are fundamentally language-processing systems, and code is a language. Education technology follows closely, as we've seen with Chegg. Healthcare IT lags significantly, constrained by HIPAA, FDA approval processes, and the high cost of clinical errors.
Projections Through 2030
By 2030, the framework projects:
- Developer Tools reach HGI 0.90 — deep in critical absorption
- Education Technology reaches 0.85 — most vertical players absorbed or marginalized
- Financial Services reaches 0.70 — entering critical absorption as AI agents handle multi-step transactions
- Healthcare IT reaches only 0.48 — still in the accelerating phase, constrained by regulation
The key insight: horizontal gravity doesn't operate uniformly. Boundary conditions — regulatory friction, open-source commoditization, and diseconomies of scope — create differential absorption rates across industries.
How to Use the HGI
For technology strategists: If your industry's HGI is approaching 0.3, begin platform integration planning. If it's above 0.5, standalone vertical strategies are increasingly risky.
For investors: HGI provides a leading indicator for vertical SaaS valuations. Companies in industries approaching critical absorption face existential pressure.
For regulators: The HGI makes the case for industry-specific AI competition policy. One-size-fits-all regulation ignores the differential dynamics across sectors.
Explore the live data on the HGI Dashboard or access it programmatically via our public API.