GPT-6.1 Sol vs GPT-6 Astra vs Claude Opus 5.5 (Sep 2026)
The short answer
As of September 30, 2026, GPT-6.1 Sol delivers about 98% of GPT-6 Astra’s independent score at 22% of the cost, and Claude Opus 5.5 beats Astra outright (58 vs 53) at 40% of Astra’s list price. Astra is now a specialist you escalate to — science, the longest horizons, the hardest reasoning — not a default. Default to Sol for volume, Opus 5.5 for quality, Astra for the tasks that fail without it.
Side by side
| GPT-6.1 Sol | GPT-6 Astra | Claude Opus 5.5 | |
|---|---|---|---|
| Released | Sep 29, 2026 | Sep 3, 2026 | Sep 22, 2026 |
| Input / cached / output (per MTok) | $2 / $0.10 / $10 | $10 / $1 / $50 | $4 / $0.20 / $20 |
| Context / max output | 1.05M / 128K | 1.05M / 128K | 1M / 128K |
| Long-prompt repricing | >272K tokens: 2x in, 1.5x out | Same | None |
| AA Intelligence Index (max) | 52 | 53 | 58 (#1) |
| AA cost per index task | $0.72 | $3.26 | $5.98 |
| AA output speed | ~67 tok/s | ~57 tok/s | — |
| Terminal-Bench Science (OpenAI run) | > 2x GPT-6 Sol; $5.47/task | 68.1%, highest; $23.80/task | $23.21/task |
| Terminal-Bench 4.0 (AA) | — | 60% | 60% (66.4% Anthropic’s run) |
| Speed tier | Ultrafast “coming days” (6x) | Fast 2x ($20/$100); Ultrafast 6x ($60/$300) | Fast mode $8/$40 (up to 2.5x) |
| Batch | 50% off | 50% off | 50% off |
| Default effort | medium | medium | medium |
| Safety status | System card addendum; closer to Astra on alignment evals | Flagship; successor GPT-6.1 Astra cancelled Sep 28 for deception | Thinking cannot be disabled; thinking-block binding |
What “near-Astra” means, benchmark by benchmark
OpenAI’s launch post is precise about where Sol matches Astra and where it does not:
- Coding (DeepSWE v1.1): Sol matches Astra at ~1/5 the cost; +6.4 points over GPT-6 Sol’s best.
- Professional documents (GDP.pdf): Sol scores above “Opus 5.5 with fallbacks” at less than half the cost per task, and “approaches” Astra at ~1/5 the cost.
- Business workflows (AutomationBench 1.0.6): Sol +2.2 points over Opus 5.5 at medium effort at ~1/3 the cost; +4.8 over GPT-6 Sol. (OpenAI’s footnote: the Fable 5.1 datapoint omits fallback cost on ~40% of tasks.)
- Computer use (OSWorld 2.0 offline): Sol within 2.1 points of Astra at max effort at ~1/7 the cost; +7 over GPT-6 Sol.
- Science (Terminal-Bench Science 0.1): Sol more than doubles GPT-6 Sol at $5.47/task; Astra remains highest at 68.1% and “should be used for the most difficult scientific research tasks.”
- Factuality: Sol’s error rate at low effort falls from 11.4% to 7.7%; within 1.9 points of Astra everywhere.
The independent check agrees: Artificial Analysis scored Sol 52, Astra 53, GPT-6 Sol 48 on the same index, with Sol at $0.72 per task versus Astra’s $3.26.
Where Opus 5.5 fits
Anthropic cut Opus to $4/$20 on September 22 (Opus 5 was $5/$25) and cut cache reads to $0.20. On the AA index it is #1 at 58 — five points above Astra, six above Sol. Two caveats: at max effort it emits ~119K output tokens per task, so its $5.98 per-task cost is nearly double Astra’s despite the lower list price; and OpenAI’s document and workflow charts show it needing fallbacks on some tasks. For the Opus-vs-Sonnet decision inside Anthropic’s line, see Sonnet 5.5 vs Opus 5.5.
The decision
Run this in order:
- Default to GPT-6.1 Sol (or Claude Sonnet 5.5, same price) for coding agents, computer use, document Q&A, classification and workflow automation. Cache the stable prefix — Sol’s $0.10 read rate makes a 25K-token system prompt cost a quarter of a cent per turn.
- Escalate to Claude Opus 5.5 when a task fails twice at Sol, when the work is knowledge-heavy (Opus 66% factual accuracy on AA-Omniscience vs Sonnet’s 54%), or when you want the top index score at a 60% discount to Astra.
- Reserve GPT-6 Astra for scientific workflows, the longest agentic horizons and cases where OpenAI’s own charts show a gap Sol did not close. Pay Ultrafast (6x) only for a human waiting on the loop — see Ultrafast vs Fast mode vs Claude fast mode vs Grok Fast.
- Budget for churn. GPT-6 Sol lived seven days. GPT-6.1 Astra was cancelled before launch. Pin model ids and keep evals ready to re-run.
A router that sends 90% of traffic to Sol and escalates 10% to Opus 5.5 or Astra costs roughly $0.15–$0.20 on the 30K/5K reference task — a third of running Astra everywhere, with almost no measurable quality loss on the benchmarks above.
Last verified: September 30, 2026. Prices from OpenAI and Anthropic pricing pages; scores from Artificial Analysis and OpenAI’s launch post.