# Grok 1.5

> xAI's 2024 reasoning upgrade: a 128K-token context window and stronger math and coding over Grok 1.

- Maker: xAI (Grok)
- Line: Grok (flagship)
- Canonical page: https://ai-tldr.dev/models/grok-1-5/
- Updated: 2026-06-18

## In short

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 has a 128K-token context window.

## Facts

| Fact | Value | Source |
| --- | --- | --- |
| Context window | 128K tokens (max output Not published by xAI) | [1] |
| Licence | Proprietary · API only | [1] |
| Released | 15 May 2024 | [2] |
| Parameters | Not disclosed | [1] |
| Knowledge cutoff | Not published by xAI | [1] |

## Sources

1. [xAI — official site](https://x.ai)
2. [Announcing Grok-1.5 — official xAI announcement](https://x.ai/news/grok-1.5)

## 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 Grok 1.5 was superseded by Grok 2 in August 2024 and is now of mainly historical interest as the version where xAI's flagship line first reached long-context, near-GPT-4-tier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.

## Benchmarks

- MATH: 50.6% ([source](https://x.ai/news/grok-1.5))
- GSM8K: 90% ([source](https://x.ai/news/grok-1.5))
- HumanEval: 74.1% ([source](https://x.ai/news/grok-1.5))

## 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) versions

- [Grok 4.3](https://ai-tldr.dev/models/grok-4-3/) (30 April 2026)
- [Grok 4.20](https://ai-tldr.dev/models/grok-4-20/) (March 2026)
- [Grok 4.1](https://ai-tldr.dev/models/grok-4-1/) (17 November 2025)
- [Grok 4](https://ai-tldr.dev/models/grok-4/) (9 July 2025)
- [Grok 3](https://ai-tldr.dev/models/grok-3/) (17 February 2025)
- [Grok 2](https://ai-tldr.dev/models/grok-2/) (20 August 2024)
- Grok 1.5 (15 May 2024) — this page
- [Grok 1](https://ai-tldr.dev/models/grok-1/) (3 November 2023)

## 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.

## Links

- [Announcing Grok-1.5 — official xAI announcement](https://x.ai/news/grok-1.5)
- [xAI — official site](https://x.ai)
- [Elon Musk's xAI unveils Grok-1.5 — Analytics India Magazine](https://analyticsindiamag.com/ai-news-updates/elon-musks-xai-unveils-grok-1-5-with-improved-reasoning-capabilities-128k-context-window/)

Source: AI/TLDR LLM registry, https://ai-tldr.dev/models/grok-1-5/