GPT-6 Pretraining Complete: 18 Months, 100k H100s, 2M Token Context
Breaking Today
Today (April 14, 2026), OpenAI officially confirmed GPT-6 pretraining completed on March 17. Pretraining lasted 18 months—far longer than GPT-5’s development cycle.
Greg Brockman (OpenAI President) subsequently confirmed the model’s existence in a podcast interview, with a single characterization: “not incremental improvement, but a major change in how we think about model development.”
Core Specifications
| Metric | Value |
|---|---|
| Parameters | 5-6 trillion (MoE, ~10% activated) |
| Activated parameters | ~230 billion |
| Context window | 2 million tokens |
| Training duration | 18 months |
| GPU cluster | ~100,000 H100s |
| Training cost | Over $20 billion |
| vs GPT-5.4 improvement | 40%+ (code/reasoning/agent) |
Symphony Architecture
GPT-6’s core highlight isn’t parameter count—it’s a fundamental architecture restructure, codenamed Symphony.
Design core:
- Native multimodal: text, images, audio, video in the same embedding space from initial design—no more “text model with a vision module bolted on”
- Dual-system reasoning: System-1 handles fast responses (fast thinking), System-2 handles logical verification and multi-step derivation (slow thinking)—echoing classic cognitive science theory
The first solves the “cobbled-together” feeling of current multimodal models. The second solves “reasoning chains breaking mid-derivation.”
2M Token Context Significance
GPT-5.4’s 1M token already solved long document processing. GPT-6 doubling that:
- can process two novellas in a single context
- fits complete transcript of 10 hours of audio
- in codebases: equivalent to fitting an entire medium-sized repo into context
Pricing
| Input | Output | |
|---|---|---|
| GPT-6 | $2.5/M token | $12/M token |
Flat with GPT-5.4—no price increase despite parameter growth.
Timeline
Official schedule:
- June 14: Public API availability (exactly 3 months after pretraining completion)
- Enterprise early access open for application now
Brockman’s quote: “GPT-6 is the last mile to AGI.” Marketing or genuine assessment? We’ll test it the moment API opens.