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GPT-5.6 Sol

OpenAI · Released Jun 2026

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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.

Is it right for you?

Good for

  • 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.

Not good for

  • 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

How it performs by task

Agentic coding

Excellent

State-of-the-art on TerminalBench 2.1 at 88.8% (91.9% Ultra). The gap over the field is real. Ultra mode's subagent decomposition is a genuine architectural advance for long-horizon coding tasks.

Cybersecurity

Excellent

Matches Mythos Preview on ExploitBench with 1/3 tokens. 96.7% CTF. Can find vulnerabilities and exploit primitives but did not autonomously produce full-chain exploits. Defensive posture by design.

Scientific reasoning (biology)

Very Good

~9-point lift over GPT-5.5 on SecureBio biology evals. Strong on GeneBench v1. Human Pathogen Capabilities at 68.4%. High risk classification means access is gated for sensitive biology workflows.

Long-horizon reasoning

Excellent

First model past 50% on Agent's Last Exam (50.9% code mode). Max reasoning mode and ultra subagent mode push reasoning depth further than any prior model.

Everyday general use

Good

Overkill for routine tasks. Terra is the better fit for daily work at half the cost with GPT-5.5-class capability. Sol should be reserved for problems where a weaker model's mistakes are expensive.

Pricing

Input

$4 / 1M tokens

Output

$20 / 1M tokens

Context

Short $4/$20 · long $8/$30 per 1M · promo

View full pricing

Benchmarks

BenchmarkScoreSource
TerminalBench 2.1 (base)88.8% Source
TerminalBench 2.1 (Ultra)91.9% Source
Agent's Last Exam (code mode)50.9% Source
SecureBio: Human Pathogen Capabilities68.4% Source
SecureBio: World-Class Biology68.3% Source
SecureBio: Molecular Biology60.0% Source
SecureBio: Virology Capabilities Test53.5% Source
Internal CTF (capture-the-flag)96.7% Source

Verdict history

Sep 23, 2026
recommended -> recommended (summary corrected: successor released): No rating change. The summary called GPT-5.6 Sol the most cost-effective frontier model. OpenAI's pricing page, fetched 23 September 2026, lists gpt-6-sol at $2/$10 per 1M short context against gpt-5.6-sol at $4/$20 (promotional through at least 21 November 2026), and the API changelog records GPT-6 Sol's release on 22 September. The deprecations page carries no notice for any GPT-5.6 model. Rating held at recommended: GPT-5.6 Sol keeps its independent coding evidence, and the successor's published scores are vendor-only so far.
Jul 16, 2026
recommended → recommended (reinforced): GPT-Red disclosure demonstrates frontier-scale safety investment alongside capability — the model was trained against an automated red-teamer achieving 84% attack success (6.5x human baseline) and emerged 6x more robust. This reinforces the existing Recommended stance rather than changing it.
Jul 12, 2026
pending -> recommended: GPT-5.6 Sol leads the DeepSWE coding-agent benchmark at 72-73% vs Fable 5's 70% at one-third the cost, and tops the AI Analysis Coding Agent Index at 80 points. These are the independent benchmarks the directory was waiting for.
Jul 12, 2026
pending -> recommended: UK AISI confirms GPT-5.6 Sol carries equivalent cyber vulnerabilities to Fable 5 — every frontier model shares this risk, which does not diminish Sol's coding and cost advantages. Vulnerability equivalence is now table stakes for frontier models.

Sources

Verification log

  • Pricing· No changes

    Automated agent

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    Automated agent

  • Pricing· Updated

    Automated agent

    Stored $4/$20 unchanged and promotional through at least 2026-11-21, but GPT-6 Sol (released 22 September 2026 per the OpenAI API changelog) and GPT-6.1 Sol now list at $2/$10, half of GPT-5.6 Sol. No deprecation listed. Verdict recommended -> conditional staged for publish on draft gpt-5-6-sol-conditional-gpt-6-sol-half-price.

  • Pricing· No changes

    Automated agent

    gpt-5.6-sol short $4/$0.40 cached/$20, long $8/$0.80/$30; promo note 'available at least through November 21, 2026' still present. Matches stored scalars and pricing_context. Summary already records GPT-6 Sol succession (verdict 2026-09-23). No update.

  • Profile· Updated

    Automated agent

    Operator-requested follow-up. Pricing page lists gpt-6-sol $2/$10 short ($4/$15 long) beside gpt-5.6-sol $4/$20 short ($8/$30 long, promo through at least Nov 21 2026); changelog records GPT-6 Sol release Sep 22; deprecations page has no GPT-5.6 notice. verdict_summary corrected via verdict_set (recommended held, 'most cost-effective frontier model' removed). Added avoid_for succeeded-by row and for_whom no-forced-migration row; sources + changelog + deprecations. Pricing scalars unchanged. last_verified_source / pricing_last_verified_source remain empty: not writable via model_update.

  • Pricing· No changes

    Automated agent

    Hot row (promo). Short $4.00 in / $0.40 cached / $20.00 out; long $8.00 / $0.80 / $30.00. Note verbatim: 'GPT-5.6 Sol's promotional pricing is available at least through November 21, 2026.' Matches stored scalars and pricing_context. No update.

  • Pricing· No changes

    Automated agent

    Hot row (promo). Short $4.00 in / $0.40 cached / $20.00 out; long $8.00 / $0.80 / $30.00; note verbatim 'GPT-5.6 Sol's promotional pricing is available at least through November 21, 2026.' Matches stored. No update.

  • Pricing· No changes

    Automated agent

    Hot row (promo). Pricing row verbatim: short input $4.00, cached $0.40, output $20.00; long input $8.00, cached $0.80, output $30.00. Promo note verbatim: 'GPT-5.6 Sol's promotional pricing is available at least through November 21, 2026.' Matches stored $4/$20 and pricing_context. No update, data_hash untouched. Stays hot until the promo resolves.

  • Pricing· No changes

    Automated agent

    Watchlist hot row (promo). Pricing page row gpt-5.6-sol, verbatim: 'Short context input $4.00 | Short context cached input $0.40 | Short context output $20.00 | Long context input $8.00 | Long context cached input $0.80 | Long context output $30.00'; promo note verbatim: 'GPT-5.6 Sol's promotional pricing is available at least through November 21, 2026.' Matches stored $4/$20, pricing_context 'Short $4/$20 · long $8/$30 per 1M · promo' and the Nov 21 strength row. No update called, data_hash untouched. Stays hot until the promo resolves.

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    Automated agent

  • Pricing· Updated

    Automated agent

    Pricing corrected against the live OpenAI API pricing page. Was $5/$30 per 1M sourced from the June launch post; live rate is $4 in / $20 out short-context and $8 in / $30 out long-context, described by OpenAI as promotional at least through November 21 2026. pricing_url repointed from the launch blog post to the developer pricing docs (platform.openai.com/docs/pricing now 301s to developers.openai.com/api/docs/pricing). Also removed pre-GA prose that contradicted the recommended verdict: the strengths and audiences still claimed no public access and ~20 preview organizations, while the model is listed among the generally available flagship models. Comparison figures refreshed: Terra $2/$12, Luna $0.20/$1.20.

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    Automated agent

  • Status· Updated

    Automated agent

    Summary re-dated to Jul 7 2026 and made explicit about what is awaited: stays pending pending GA + independent benchmarks; still government-gated (~20 orgs); Sol Ultra confirmed for Codex Jul 6 by Sottiaux, prediction markets pricing Jul 9 GA (unconfirmed). Verdict unchanged (pending).

  • Pricing· No changes

    Automated agent

  • Pricing· No changes

    Automated agent

    Pricing unchanged: $5/$30 per 1M tokens. Government-gated limited preview (~20 orgs). Confirmed by OpenAI blog and aipricing.guru.

  • Profile· No changes

    Imported at launch

How we evaluate