Overview
Grok 1.5 is the second model in xAI's flagship Grok line, announced on March 28, 2024 and rolled out to Grok users on the X (formerly Twitter) platform in the weeks that followed. It was positioned as a reasoning-focused upgrade to Grok 1, the model xAI later open-sourced under Apache 2.0. Unlike Grok 1, the weights for Grok 1.5 were never released — it is a proprietary model.
The headline change in Grok 1.5 was its context window, which jumped to 128,000 tokens — roughly a sixteen-fold increase over Grok 1. In xAI's Needle-in-a-Haystack retrieval tests, Grok 1.5 recovered embedded information with perfect accuracy across the full 128K-token window. The model also posted clear gains on math and coding evaluations, with xAI reporting 50.6% on MATH, 90% on GSM8K and 74.1% on HumanEval.
Grok 1.5 reached users only through the Grok chatbot for X Premium subscribers; xAI did not publish a developer API or per-token pricing for the text model at this stage (the public xAI API arrived later with the Grok 2 generation). Grok 1.5 was superseded by Grok 2 in August 2024 and is now of mainly historical interest as the version where xAI's flagship line first reached long-context, near-GPT-4-tier reasoning.
| Released | 2024-05-15 |
|---|---|
| License | Proprietary |
| Weights | API only |
| Parameters | Not disclosed |
| Context | 128K tokens |
| Max output | Not published by xAI |
| Architecture | Proprietary transformer-based large language model, an iteration on Grok 1. xAI trained it on a custom distributed training stack built on JAX, Rust and Kubernetes. The exact parameter count and whether 1.5 retained Grok 1's mixture-of-experts design were not disclosed. |
| Knowledge cutoff | Not published by xAI |
| Modalities | Text |
| Status | Superseded — replaced by Grok 2 (August 2024) and later flagship Grok releases. The text model was never offered through a public API and is no longer the current Grok. |
Benchmarks
Scores on a 0–100 scale (25-point gridlines); higher is better. Each benchmark links to its published source.
Strengths
- 128K-token context window — a 16x jump over Grok 1 — with perfect Needle-in-a-Haystack retrieval across the full window
- Strong grade-school-to-competition math: 90% on GSM8K and 50.6% on the harder MATH set
- Solid code generation for its era (74.1% on HumanEval)
- Marked reasoning improvement over Grok 1, bringing xAI's flagship line close to GPT-4-tier performance
Best for
- Long-document analysis and retrieval that needed a large context window in 2024
- Math and reasoning tasks, from word problems to competition-style problems
- Code generation and programming help inside the Grok chatbot
- General conversational assistance for X Premium subscribers
Grok (flagship) — every version
The full lineage of the Grok (flagship) line, newest first. Every version has its own page — click any to compare specs, benchmarks and pricing.
| Version | Released | Context | License |
|---|---|---|---|
| Grok 4.6current | 2026-08-12 | 500K | Proprietary |
| Grok 4.5 | 2026-07-09 | — | Proprietary |
| Grok 4.3 | 2026-04-30 | 1M | Proprietary |
| Grok 4.20 | 2026-03 | — | Proprietary |
| Grok 4.1 | 2025-11-17 | — | Proprietary |
| Grok 4 | 2025-07-09 | — | Proprietary |
| Grok 3 | 2025-02-17 | — | Proprietary |
| Grok 2 | 2024-08-20 | — | Open weights |
| Grok 1.5 | 2024-05-15 | — | Proprietary |
| Grok 1 | 2023-11-03 | — | Apache-2.0 |
FAQ
When was Grok 1.5 released?
xAI announced Grok 1.5 on March 28, 2024, and made it available to Grok users on the X platform over the following weeks (around May 2024).
What is Grok 1.5's context window?
Grok 1.5 has a 128,000-token context window — about sixteen times larger than Grok 1's. In xAI's Needle-in-a-Haystack tests it retrieved embedded information with perfect accuracy across the full window.
Are Grok 1.5's weights open?
No. Unlike Grok 1, whose weights xAI open-sourced under Apache 2.0 in March 2024, Grok 1.5 is a proprietary model and its weights were never released.
Could you use Grok 1.5 through an API?
No public API or per-token pricing was published for the Grok 1.5 text model. It was accessible only through the Grok chatbot for X Premium subscribers; xAI's developer API came later with the Grok 2 generation.