GPT-5.6 vs Claude Opus 4.8
Both generally available — the real numbers
As of 2026-10-07, neither is its maker's newest flagship: OpenAI has since released the GPT-6 series (GPT-6 Astra on 2026-09-03, GPT-6 Sol and GPT-6 Luna on 2026-09-22, GPT-6.1 Sol on 2026-09-29), and Anthropic's newest Opus is Claude Opus 5.5 (launched 2026-09-22), with Opus 4.8 now listed as a legacy model that is still available. Below is the historical comparison of Claude Opus 4.8 and GPT-5.6 (Sol / Terra / Luna), with the verified numbers unchanged and anything unpublished clearly marked.
Two flagships, in one line
OpenAI previewed GPT-5.6 on June 26 and made all three tiers (Sol / Terra / Luna) GA on July 9, 2026. Sol leads Terminal-Bench 2.1 at 88.8% at the launch price of $5/$30 — the 2026-09-12 archive of the official pricing page shows $4/$20, promotional at least through 2026-11-21 — with an official 1.05M API context and 128K max output.
Anthropic's generally available flagship (May 28, 2026): $5/$25, native 1M context, Fast Mode (~2.5x speed, ~3x cheaper), dynamic workflows and effort control.
Spec comparison
Both are GA; any still-unpublished specs are marked accordingly.
| Spec | GPT-5.6 | Claude Opus 4.8 |
|---|---|---|
| Release status | GA (2026-07-09) | GA (2026-05-28) |
| Context window | 1.05M (API) | 1M (native) |
| Pricing / MTok (Sol) | $4 / $20 (Sol, promo at least through 2026-11-21) | $5 / $25 |
| Terminal-Bench 2.1 | 88.8% (Sol) | 78.9% |
| Signature capability | Sol / Terra / Luna tiers | Dynamic workflows + Fast Mode |
| QCode access | Live · Codex + API | Supported now · Claude Code |
GPT-5.6 figures are from OpenAI's official release and docs — the 1.05M API context window and 128K max output are now official. Opus 4.8's Terminal-Bench 78.9% is the published cross-comparison figure.
✅ What's confirmed
Both models now have full data. Opus 4.8 is GA — $5/$25, 1M context, Fast Mode, dynamic workflows, Terminal-Bench 78.9%. GPT-5.6 Sol went GA on July 9 with Terminal-Bench 88.8% at the then price of $5/$30 (the 2026-09-12 archive of the official pricing page shows $4/$20, promotional at least through 2026-11-21). Sol leads that benchmark, while Opus 4.8 remains many teams' pick for deep refactors and judgment-heavy work — and now you can use both.
🔮 What's still unverified
The preview-era open questions are settled: GA landed on July 9, 2026; the API context window is officially 1.05M (128K max output); and OpenAI confirmed Sol runs on Cerebras at ~750 tokens/s in July.
Context: Fable 5 is back; Mythos 5 stays limited
One more variable: Anthropic's Fable 5 was suspended worldwide on June 12, 2026 under a regulatory directive and restored on July 15, 2026 — it now sits above Opus 4.8 as Anthropic's top tier. Note that Anthropic has tiered Fable 5 by plan on its own subscriptions since July 19 (the API is unaffected), while Mythos 5 remains limited to approved organizations. See the AI Model Radar for the live picture.
Access both sides with QCode
No need to pick one. A single QCode key runs Claude Opus 4.8 in Claude Code and GPT-5.6 Sol / Terra in Codex CLI; as of 2026-10-07 the same key also calls claude-opus-5-5 and gpt-6.1-sol.
export ANTHROPIC_BASE_URL="https://api.qcode.cc/api"
export ANTHROPIC_AUTH_TOKEN="$QCODE_KEY"
claudenpm install -g @openai/codex
# add QCode profile in ~/.codex/config.toml
codex --profile qcodeComparison FAQ
How does GPT-5.6 compare to Opus 4.8 on benchmarks?
On Terminal-Bench 2.1, GPT-5.6 Sol scores 88.8% versus Opus 4.8 at 78.9%. Both are GA now, so the practical choice depends on your workload: Sol leads terminal agent tasks, while many teams still prefer Opus 4.8 for deep refactors and judgment-heavy work.
Is GPT-5.6 generally available?
Yes — since July 9, 2026, all three GPT-5.6 tiers (Sol / Terra / Luna) are generally available via the API and Codex; Opus 4.8 has been GA since May 28. On QCode, claude-opus-4-8, gpt-5.6-sol and gpt-5.6-terra run on a single key. QCode does not currently support gpt-6-luna or gpt-5.6-luna (both removed from /models); please use another GPT model, such as gpt-6.1-sol, gpt-6-sol or gpt-5.6-terra.
How much do they cost?
Per million tokens: GPT-5.6 Sol is now $4 / $20 (per the 2026-09-12 archive of the official pricing page, promotional at least through 2026-11-21); Claude Opus 4.8 is $5 / $25. GPT-5.6's cheaper Terra ($2/$12) and Luna ($0.20/$1.20) tiers target lower-cost workloads.
Which should I use right now?
As of 2026-10-07 both are usable, but both have newer successors: OpenAI's models page says to start with GPT-6 Astra if you are not sure, and Anthropic's models overview says to start with Claude Opus 5.5 for most workloads. On QCode, claude-opus-4-8 and gpt-5.6-sol, plus claude-opus-5-5, gpt-6-astra and gpt-6.1-sol, all run on one key — try both sides without changing accounts.
One key, miss neither side
Sign up for QCode — one key for Claude Opus 4.8 and GPT-5.6 Sol, plus Claude Opus 5.5, GPT-6 Sol and GPT-6.1 Sol.