GPT-5.1 Codex High vs Mercury 3
GPT-5.1 Codex High and Mercury 3 are closely matched at 29.1 and 36.1 on the LLM Stats Score. Mercury 3 is 21.2x cheaper per token.
OpenAI · Inception · Updated for 2026
Which is better?
GPT-5.1 Codex High and Mercury 3 are closely matched on the overall LLM Stats Score at 29.1 and 36.1.
On price, Mercury 3 is roughly 21.2x cheaper per token on a blended 3:1 input/output basis, which adds up quickly at production volume.
Mercury 3 also accepts a larger context window (1,000,000 input tokens), making it the stronger choice for long documents and large codebases.
Based on current LLM Stats indexes, shared benchmarks, pricing, and model metadata for 2026.
Choose GPT-5.1 Codex High
- you want predictable pricing at $1.25/M input and $10.00/M output
Choose Mercury 3
- cost matters — it's about 21.2x cheaper per token
- you process long inputs — it offers a 1,000,000 token context window
- you want the most recent training data — it shipped Oct 2026
At a glance
The differences that matter most.
Individual benchmarks
1 reported for GPT-5.1 Codex High · 12 for Mercury 3
GPT-5.1 Codex High 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
Pricing Analysis
Price comparison per million tokens
For input processing, GPT-5.1 Codex High ($1.25/1M tokens) is 12.5x more expensive than Mercury 3 ($0.10/1M tokens).
For output processing, GPT-5.1 Codex High ($10.00/1M tokens) is 28.6x more expensive than Mercury 3 ($0.35/1M tokens).
In conclusion, GPT-5.1 Codex High is more expensive than Mercury 3.*
* Using a 3:1 ratio of input to output tokens
Context Window
Maximum input and output token capacity
Mercury 3 accepts 1,000,000 input tokens compared to GPT-5.1 Codex High's 400,000 tokens. Mercury 3 can generate longer responses up to 131,072 tokens, while GPT-5.1 Codex High is limited to 128,000 tokens.
Input capabilities
Documented input modalities across available providers
GPT-5.1 Codex High supports multimodal inputs, whereas Mercury 3 does not.
GPT-5.1 Codex High can handle both text and other forms of data like images, making it suitable for multimodal applications.
GPT-5.1 Codex High
Mercury 3
License
Usage and distribution terms
Both models are licensed under proprietary licenses.
Both models have usage restrictions defined by their respective organizations.
Proprietary
Closed source
Proprietary
Closed source
Release Timeline
When each model was launched
GPT-5.1 Codex High was released on 2025-11-12, while Mercury 3 was released on 2026-10-19.
Mercury 3 is 11 months newer than GPT-5.1 Codex High.
Nov 12, 2025
11 months ago
Oct 19, 2026
1 days ago
11mo newerKnowledge Cutoff
When training data ends
Neither model specifies a knowledge cutoff date.
Unable to compare the recency of their training data.
Provider Availability
GPT-5.1 Codex High is available from OpenAI. Mercury 3 is available from Inception.
GPT-5.1 Codex High
Mercury 3
Outputs Comparison
Judge for yourself.
Run your own prompts against GPT-5.1 Codex High and Mercury 3 side-by-side, then vote on the output you prefer.
FAQ
Common questions about GPT-5.1 Codex High vs Mercury 3.