QUICK VERDICT — JULY 2026
● Better benchmark (Terminal-Bench 2.1): GPT-5.6 Terra at 87.1% vs Sonnet 5 at 78.4%
● Better coding accuracy (SWE-bench Pro): Claude Sonnet 5 at 63.2% — Terra's SWE-bench Pro not published
● Better price until August 31: Claude Sonnet 5 at $2/$10/M intro
● After August 31: Both price at $3/$15/M — the comparison resets to pure capability
● Better context window: GPT-5.6 Terra at 1.05M vs Sonnet 5 at 1M (marginal)
● Best default mid-tier until August 31: Claude Sonnet 5 — lower price, published coding accuracy
● Best mid-tier after August 31: GPT-5.6 Terra — Terminal-Bench lead at same price
Full Comparison Table
| Model |
Input /1M |
Output /1M |
Context |
Terminal-Bench 2.1 |
SWE-bench Pro |
| Claude Sonnet 5 (intro) |
$2 (until Aug 31) |
$10 (until Aug 31) |
1M |
78.4% |
63.2% |
| Claude Sonnet 5 (standard) |
$3 (from Sep 1) |
$15 (from Sep 1) |
1M |
78.4% |
63.2% |
| GPT-5.6 Terra |
$2.50 |
$15 |
1.05M |
87.1% |
Not published |
Sonnet 5 intro pricing ($2/$10/M) ends August 31, 2026 — steps to $3/$15/M. Terra at $2.50/$15/M is permanent pricing. After August 31 the input price difference is $0.50/M — Sonnet 5 input is cheaper but output is identical.
The Benchmark Gap
GPT-5.6 Terra leads Terminal-Bench 2.1 (87.1% vs Sonnet 5's 78.4%) — an 8.7-point gap on the broadest software engineering benchmark. That is a meaningful lead across a wide range of coding and reasoning tasks. The METR reward-hacking caveat applies to the Sol line primarily; Terra's Terminal-Bench score has not been specifically flagged. Claude Sonnet 5 leads on SWE-bench Pro (63.2% published) — OpenAI has not published Terra's SWE-bench Pro score, making direct comparison on the most trusted agentic coding benchmark impossible. For production coding workloads where task completion rate matters, Sonnet 5's published 63.2% is the only available verified number.
The Pricing Timeline — Act Before August 31
The most important date in this comparison is August 31. Sonnet 5's intro pricing ($2/$10/M) ends that day — after which it becomes $3/$15/M, identical to GPT-5.6 Terra's permanent pricing on output and $0.50/M more expensive on input. Between now and August 31, Sonnet 5 is significantly cheaper: $2 vs $2.50 input, $10 vs $15 output. A team running 10 million output tokens per month saves $50,000 per month by using Sonnet 5 over Terra in that window. After August 31, the economic comparison resets and Terra's Terminal-Bench 2.1 lead becomes the primary differentiator.
Which to Use
Until August 31 — default to Claude Sonnet 5 ($2/$10/M). Lower price on both input and output, published SWE-bench Pro score. For any production workload starting before September, Sonnet 5 is the rational default.
After August 31 — benchmark both on your actual workloads. When Sonnet 5 steps to $3/$15/M, the comparison becomes Terminal-Bench lead (Terra, 87.1%) vs SWE-bench Pro published accuracy (Sonnet 5, 63.2%) at nearly identical pricing. The right choice depends on your specific task mix.
For broad software engineering tasks: GPT-5.6 Terra. The 8.7-point Terminal-Bench 2.1 lead is consistent and meaningful for coding, debugging, and general software work.
For agentic coding with human review: Claude Sonnet 5. 63.2% SWE-bench Pro is the only published, neutrally verified agentic coding score in this price tier. Until OpenAI publishes Terra's SWE-bench Pro, Sonnet 5 is the only option with a verified task completion rate for autonomous coding.
Last updated July 2026. Related: Claude Fable 5 vs GPT-5.6 Sol → · Fable 5 credit pricing from July 20 → · Budget tier: Gemini 3.6 Flash vs 3.5 Flash vs Luna →