# GPT-5.6 Sol

OpenAI, released 2026-06-26

**Verdict: recommended.** GPT-5.6 Sol is no longer OpenAI's best-value frontier model: its successor GPT-6 Sol, released 22 September 2026, lists at $2/$10 per 1M tokens against Sol's $4/$20. It stays recommended because its coding lead has third-party backing, while every GPT-6 Sol score so far is OpenAI's own. OpenAI lists no deprecation, and the $4/$20 rate is promotional through at least 21 November 2026. Test GPT-6 Sol before committing new workloads. Last verified 2026-06-27.

## Pricing

- Input: $4 / 1M tokens
- Output: $20 / 1M tokens
- Context: Short $4/$20 · long $8/$30 per 1M · promo

## Strengths

- TerminalBench 2.1 state-of-the-art: 88.8% base, 91.9% in Ultra subagent mode — clears Mythos 5 (88.0%) and Fable 5 (84.3%). Sol Ultra is >3 points ahead of any competitor.
- Long-horizon coding and agentic tasks: first model past the halfway mark on Agent's Last Exam (50.9%), with max reasoning and subagent-based ultra mode for decomposing hard problems.
- Cybersecurity and vulnerability research: matches Anthropic Mythos Preview on ExploitBench with roughly 1/3 the output tokens. CTF score of 96.7% on internal testing. Strong exploit primitive discovery in Chromium and Firefox without crossing into autonomous full-chain exploitation.
- Biology and scientific reasoning: ~9 point overall lift over GPT-5.5 on SecureBio evaluations (Human Pathogen 68.4%, Molecular Biology 60.0%). Stronger on GeneBench v1 while using fewer tokens. Useful for legitimate biomedical research under trusted access programs.
- Controlled release with heavy safety stack: activation classifiers, real-time misuse screening, 700K A100e GPU-hour automated red teaming, and layered model-level refusals. Heavily hardened against adversarial attacks with defensive cyber posture.
- Prompt caching overhaul: explicit cache breakpoints, 30-minute minimum cache life, cache writes at 1.25x input rate, cache reads at 90% discount. Makes long-running agentic sessions far more predictable on cost.
- Long-context work costs roughly double: past the short-context tier the rate steps from $4/$20 to $8/$30 per 1M tokens. Budget by context length, not just request volume.
- Untested on real-world messy codebases: all published benchmarks are vendor-run under vendor harnesses. The 0.8-point gap over Mythos 5 on TerminalBench is within measurement noise — these are a statistical tie.
- At $4/$20 per 1M tokens Sol is priced for the hardest tasks. GPT-5.6 Terra delivers GPT-5.5-class performance at $2/$12, and Luna at $0.20/$1.20 — reserve Sol for problems where a weaker model's mistakes are expensive. OpenAI states current pricing is promotional at least through November 21 2026.
- New deployments chosen on price: its successor GPT-6 Sol, released 22 September 2026, lists at $2/$10 per 1M tokens short context, half GPT-5.6 Sol's $4/$20

## Benchmarks

- TerminalBench 2.1 (base): 88.8% (https://openai.com/index/previewing-gpt-5-6-sol/)
- TerminalBench 2.1 (Ultra): 91.9% (https://openai.com/index/previewing-gpt-5-6-sol/)
- Agent's Last Exam (code mode): 50.9% (https://venturebeat.com/technology/openai-unveils-gpt-5-6-sol-terra-and-luna-models-but-only-accessible-to-limited-preview-partners-for-now-per-us-gov)
- SecureBio: Human Pathogen Capabilities: 68.4% (https://lushbinary.com/blog/gpt-5-6-sol-benchmarks-terminalbench-agentic-deep-dive/)
- SecureBio: World-Class Biology: 68.3% (https://lushbinary.com/blog/gpt-5-6-sol-benchmarks-terminalbench-agentic-deep-dive/)
- SecureBio: Molecular Biology: 60.0% (https://lushbinary.com/blog/gpt-5-6-sol-benchmarks-terminalbench-agentic-deep-dive/)
- SecureBio: Virology Capabilities Test: 53.5% (https://lushbinary.com/blog/gpt-5-6-sol-benchmarks-terminalbench-agentic-deep-dive/)
- Internal CTF (capture-the-flag): 96.7% (https://venturebeat.com/technology/openai-unveils-gpt-5-6-sol-terra-and-luna-models-but-only-accessible-to-limited-preview-partners-for-now-per-us-gov)

## Sources

- [OpenAI: GPT-5.6 Preview System Card](https://deploymentsafety.openai.com/gpt-5-6-preview)
- [OpenAI — Previewing GPT-5.6 Sol](https://openai.com/index/previewing-gpt-5-6-sol/)
- [OpenAI Docs: API changelog (Decisions API beta, October 6, 2026)](https://developers.openai.com/api/docs/changelog)
- [TechCrunch — OpenAI limits GPT-5.6 rollout after government request](https://techcrunch.com/2026/06/26/openai-limits-gpt-5-6-rollout-after-government-request-says-restrictions-shouldnt-be-the-norm/)
- [OpenAI API pricing](https://developers.openai.com/api/docs/pricing)
- [VentureBeat: GPT-5.6 Sol, Terra and Luna models](https://venturebeat.com/technology/openai-unveils-gpt-5-6-sol-terra-and-luna-models-but-only-accessible-to-limited-preview-partners-for-now-per-us-gov)
- [Lushbinary: GPT-5.6 Sol Benchmarks Deep Dive](https://lushbinary.com/blog/gpt-5-6-sol-benchmarks-terminalbench-agentic-deep-dive/)
- [OpenAI API docs: Deprecations](https://developers.openai.com/api/docs/deprecations)

Canonical: https://neomanex.com/models/gpt-5-6-sol