Model Comparison
GPT-5.6 Terra vs Mercury 2Which is better in 2026?
GPT-5.6 Terra significantly outperforms across most benchmarks. Mercury 2 is 15.0x cheaper per token.
Verdict: GPT-5.6 Terra vs Mercury 2 — which is better?
GPT-5.6 Terra (by OpenAI) and Mercury 2 (by Inception) are two of the AI models people compare most. Here is how they stack up on benchmarks, price and capabilities, and which one to pick in 2026.
GPT-5.6 Terra outperforms in 1 benchmarks (GPQA), while Mercury 2 is better at 0 benchmarks. GPT-5.6 Terra significantly outperforms across most benchmarks.
On price, Mercury 2 is roughly 15.0x cheaper per token on a blended 3:1 input/output basis, which adds up quickly at production volume.
GPT-5.6 Terra also accepts a larger context window (1,050,000 input tokens), making it the stronger choice for long documents and large codebases.
Choose GPT-5.6 Terra if…
- you want the strongest raw capability — it leads on 1 of 1 shared benchmarks
- you process long inputs — it offers a 1,050,000 token context window
- you want the most recent training data — it shipped Jul 2026
Choose Mercury 2 if…
- cost matters — it's about 15.0x cheaper per token
Performance Benchmarks
Comparative analysis across standard metrics
GPT-5.6 Terra outperforms in 1 benchmarks (GPQA), while Mercury 2 is better at 0 benchmarks.
GPT-5.6 Terra significantly outperforms across most benchmarks.
Arena Performance
Human preference votes
Pricing Analysis
Price comparison per million tokens
For input processing, GPT-5.6 Terra ($2.50/1M tokens) is 10.0x more expensive than Mercury 2 ($0.25/1M tokens).
For output processing, GPT-5.6 Terra ($15.00/1M tokens) is 20.0x more expensive than Mercury 2 ($0.75/1M tokens).
In conclusion, GPT-5.6 Terra is more expensive than Mercury 2.*
* Using a 3:1 ratio of input to output tokens
Context Window
Maximum input and output token capacity
GPT-5.6 Terra accepts 1,050,000 input tokens compared to Mercury 2's 128,000 tokens. GPT-5.6 Terra can generate longer responses up to 128,000 tokens, while Mercury 2 is limited to 8,192 tokens.
Input Capabilities
Supported data types and modalities
GPT-5.6 Terra supports multimodal inputs, whereas Mercury 2 does not.
GPT-5.6 Terra can handle both text and other forms of data like images, making it suitable for multimodal applications.
GPT-5.6 Terra
Mercury 2
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-5.6 Terra was released on 2026-07-09, while Mercury 2 was released on 2026-02-24.
GPT-5.6 Terra is 5 months newer than Mercury 2.
Jul 9, 2026
2 weeks ago
4mo newerFeb 24, 2026
5 months ago
Knowledge Cutoff
When training data ends
GPT-5.6 Terra has a documented knowledge cutoff of 2026-02-16, while Mercury 2's cutoff date is not specified.
We can confirm GPT-5.6 Terra's training data extends to 2026-02-16, but cannot make a direct comparison without Mercury 2's cutoff date.
Feb 2026
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Provider Availability
GPT-5.6 Terra is available from OpenAI. Mercury 2 is available from Inception.
GPT-5.6 Terra
Mercury 2
Outputs Comparison
Key Takeaways
Mercury 2
View detailsInception
Detailed Comparison
Interactive Arena
Judge for yourself.
Run your own prompts against GPT-5.6 Terra and Mercury 2 side-by-side, then vote on the output you prefer.
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FAQ
Common questions about GPT-5.6 Terra vs Mercury 2.