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GPT-5 Codex vs Mercury 3

GPT-5 Codex and Mercury 3 are closely matched at 26.5 and 36.1 on the LLM Stats Score.

OpenAI · Inception · Updated for 2026

Which is better?

GPT-5 Codex and Mercury 3 are closely matched on the overall LLM Stats Score at 26.5 and 36.1.

Based on current LLM Stats indexes, shared benchmarks, pricing, and model metadata for 2026.

Choose GPT-5 Codex

  • you are already invested in the OpenAI ecosystem

Choose Mercury 3

  • you want the most recent training data — it shipped Oct 2026

At a glance

The differences that matter most.

GPT-5 Codex
OpenAI
Mercury 3
Inception
Core performance indexes
LLM Stats Score
26.5
#170
36.1
#98
Reasoning
26.4
#169
34.8
#103
Coding
19.3
#122
21.5
#105
Cost, coverage & limits
Benchmark wins
—
—
Input price
— / M
$0.10 / M
Output price
— / M
$0.35 / M
Context window
—
1,000,000

Individual benchmarks

1 reported for GPT-5 Codex · 12 for Mercury 3

No common benchmarks found

GPT-5 Codex and Mercury 3don't have any common benchmark datasets to compare. They may have been evaluated on different testing suites.

Human preference

Blind head-to-head votes and playground preference scores

Context Window

Maximum input and output token capacity

Only Mercury 3 specifies input context (1,000,000 tokens). Only Mercury 3 specifies output context (131,072 tokens).

OpenAI
GPT-5 Codex
Input- tokens
Output- tokens
Inception
Mercury 3
Input1,000,000 tokens
Output131,072 tokens
Sat Oct 24 2026 • llm-stats.com

License

Usage and distribution terms

Both models are licensed under proprietary licenses.

Both models have usage restrictions defined by their respective organizations.

GPT-5 Codex

Proprietary

Closed source

Mercury 3

Proprietary

Closed source

Release Timeline

When each model was launched

GPT-5 Codex was released on 2025-09-15, while Mercury 3 was released on 2026-10-19.

Mercury 3 is 13 months newer than GPT-5 Codex.

GPT-5 Codex

Sep 15, 2025

1.1 years ago

Mercury 3

Oct 19, 2026

5 days ago

1.1yr newer

Knowledge Cutoff

When training data ends

GPT-5 Codex has a documented knowledge cutoff of 2024-09-30, while Mercury 3's cutoff date is not specified.

We can confirm GPT-5 Codex's training data extends to 2024-09-30, but cannot make a direct comparison without Mercury 3's cutoff date.

GPT-5 Codex

Sep 2024

Mercury 3

—

Outputs Comparison

Notice missing or incorrect data?

Judge for yourself.

Run your own prompts against GPT-5 Codex and Mercury 3 side-by-side, then vote on the output you prefer.

GPT-5 Codex
✓ Preferred
Mercury 3
Open in Playground

FAQ

Common questions about GPT-5 Codex vs Mercury 3.

Which is better, GPT-5 Codex or Mercury 3?

GPT-5 Codex and Mercury 3 are closely matched on the LLM Stats Score at 26.5 and 36.1. GPT-5 Codex is made by OpenAI and Mercury 3 is made by Inception. The best choice depends on your use case — compare their capability indexes, individual benchmarks, pricing, and limits above.

How does GPT-5 Codex compare to Mercury 3 in benchmarks?

GPT-5 Codex scores SWE-Bench Verified: 74.5%. Mercury 3 scores GPQA: 89.2%, AA-LCR: 77.7%, IFBench: 76.8%, MRCR v2: 75.5%, DeepSearchQA: 71.3%.

What are the context window sizes for GPT-5 Codex and Mercury 3?

GPT-5 Codex supports an unknown number of tokens and Mercury 3 supports 1.0M tokens. A larger context window lets you process longer documents, conversations, or codebases in a single request.

What are the main differences between GPT-5 Codex and Mercury 3?

Key differences include LLM Stats Score (26.5 vs 36.1). See the full comparison above for benchmark-by-benchmark results.

Who makes GPT-5 Codex and Mercury 3?

GPT-5 Codex is developed by OpenAI and Mercury 3 is developed by Inception.

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