SeaWorkGrok 4.5 vs Claude Fable 5 vs GPT-5.6 for Coding (2026)
An honest, sourced comparison of Grok 4.5, Claude Fable 5, and GPT-5.6 for coding — price, speed, benchmarks, and when to pick which. Most people should run more than one; here's how to match the model to the task.
Grok 4.5, Claude Fable 5, and GPT-5.6 are the three flagship coding models that matter in mid-July 2026 — and the honest answer to “which is best” is that they win different axes. Grok 4.5 wins on price and speed; Fable 5 wins on hard SWE-Bench Pro work; GPT-5.6 wins on tiered economics and terminal/agentic scores. Below: a fair table, concrete pick rules, and why “use more than one” is the common real answer.
That’s the summary if you only wanted the verdict. The rest is the comparison without the fan-war.
The short answer
- Pick Grok 4.5 when you want strong coding at $2 / $6 per MTok and ~80 TPS, especially high-volume agent loops where wall-clock and output tokens dominate cost (SpaceXAI).
- Pick Claude Fable 5 when the task is hard, repo-level engineering and one-pass correctness is worth $10 / $50 — it still leads SWE-Bench Pro by a wide margin (Anthropic).
- Pick GPT-5.6 when you want a three-tier ladder (Sol / Terra / Luna) inside one family, with Sol leading Terminal-Bench 2.1 among the OpenAI tiers (OpenAI / Vellum).
Most people end up mixing all three across a week of work.
Head to head
Numbers below are from vendor announcements and independent roundups. Treat them as a rough ranking — harnesses differ, and labs emphasize the benchmarks they win.
| Dimension | Grok 4.5 | Claude Fable 5 | GPT-5.6 (Sol unless noted) |
|---|---|---|---|
| Released | July 8, 2026 (SpaceXAI) | June 9 / redeployed July 1, 2026 (Anthropic) | July 9, 2026 (MarkTechPost) |
| Pricing (per Mtok in/out) | $2 / $6 (cached in $0.50) (docs) | $10 / $50 (batch $5 / $25) (finout) | $5 / $30 Sol; $2.50 / $15 Terra; $1 / $6 Luna (Vellum) |
| Speed | ~80 TPS claimed (SpaceXAI) | Not the pitch — optimized for hard, sustained work | Tier-dependent; Luna is the speed/cost tier |
| Context | 500K (docs) | Claude 5 family (see Anthropic docs for current window) | OpenAI GPT-5.6 family (see OpenAI docs for current window) |
| Terminal-Bench 2.1 | 83.3% (SpaceXAI chart) | Fable max 84.3% on SpaceXAI’s chart; Anthropic/independent figures vary | Sol 88.8%, Sol Ultra 91.9% (Vellum) |
| SWE-Bench Pro | 64.7% (SpaceXAI) | 80.3–80.4% (Anthropic; SpaceXAI chart) | Sol 64.6% in one roundup (Vellum); GPT-5.5 xhigh 58.6% on SpaceXAI’s chart |
| SWE Marathon (pass@1) | 29.0% (leads SpaceXAI’s chart) | Fable max 24.0% on that chart | Not the headline OpenAI metric for 5.6 |
| Token thrift | ~4.2× fewer avg output tokens vs Opus 4.8 max on SWE-Bench Pro tasks (SpaceXAI) | Premium per-token; wins when it finishes in fewer rounds | Terra/Luna exist so you don’t pay Sol rates for mechanical work |
| Best-fit tasks | High-volume coding agents, cost-sensitive loops, Cursor / Grok Build defaults | Hard, long, repo-level engineering | Terminal/agentic loops; mix Sol+Terra+Luna by difficulty |
| How you get it | Grok Build, Cursor, SpaceXAI API | Claude Code, Claude.ai, API | Codex, API |
| EU note | Not available in EU at launch (SpaceXAI) | Available globally post-redeploy | Available via OpenAI products (check regional terms) |
Three caveats before you weaponize this table. First, different labs publish different benchmarks — when they win a chart they cite it; when they lose they question the harness. Second, “max” / “xhigh” / “Ultra” modes often spend more compute (or spawn subagents) than a single default pass — Sol Ultra’s 91.9% is the expensive mode. Third, vendor charts are not your monorepo. Run a real task on each before you rewrite your defaults.
Setup deep dive for Grok only: How to use Grok 4.5 for coding. Agent-product comparison (Grok Build vs Claude Code vs Codex): separate article.
When to pick Grok 4.5
Grok 4.5’s real advantage is intelligence per dollar per minute, not topping every hard-coding leaderboard.
- Cost ceiling. At $2 / $6 it undercuts Fable 5 by roughly 5× on list rates and undercuts Sol on both sides of the ledger. If an agent burns millions of tokens a day, that gap is the whole strategy.
- Fast agent loops. ~80 TPS plus the claimed token efficiency means shorter waits and fewer output tokens on the same class of tasks — exactly what you want for iterative tool-calling runs.
- You’re already in Cursor or Grok Build. It’s the launch default there; friction is zero (SpaceXAI).
Don’t pick it as a religion on the hardest one-shot refactors where Fable 5’s SWE-Bench Pro lead is the number that matters. Don’t pick it if you need EU access today.
When to pick Claude Fable 5
Fable 5 earns its $10 / $50 when flailing is more expensive than tokens.
- Hard, production-standard engineering. The ~80% SWE-Bench Pro band is still the clearest published lead on difficult repo work among these three.
- Long, high-stakes runs. One correct pass can be cheaper than three cheap wrong ones — even at double the per-token rate of lesser models.
- Claude Code is already your home. Update, select Fable 5, go (Anthropic).
It is overkill for boilerplate, doc passes, and mechanical renames — that work belongs on Grok 4.5, GPT-5.6 Luna/Terra, or another cheaper model.
When to pick GPT-5.6
GPT-5.6’s unique product is the tier family, not a single score.
- Mixed-difficulty days. Terra for everyday features, Luna for churn, Sol (or Sol Ultra) only when the task is worth flagship rates.
- Terminal-Bench-shaped work. Sol’s 88.8% (Ultra 91.9%) is the OpenAI headline for agentic terminal work (Vellum).
- Codex is already wired in. Same key, same quota — pick the tier.
If you only ever need one price point and care more about raw hard-coding rank than tiers, Fable 5 or Grok 4.5 may fit cleaner.
How people actually mix them
Here’s the observation the leaderboard wars miss: almost nobody ships a week of real work on a single model.
A sane default mix for mid-2026:
| Work type | Reasonable first pick | Why |
|---|---|---|
| High-volume agent loops, tests | Grok 4.5 | $2/$6 + speed |
| Everyday features in Codex | GPT-5.6 Terra | Half-ish Sol quality at half Sol price |
| Boilerplate / docs / renames | GPT-5.6 Luna or Grok 4.5 | Cost floor |
| Hard cross-cutting refactor | Claude Fable 5 | SWE-Bench Pro lead |
| Terminal-heavy multi-step agent | GPT-5.6 Sol (or Ultra) | Terminal-Bench headline |
The useful skill is not “declare a winner” — it is routing the task to the model whose economics and strengths match the failure mode. Wrong model is either burning money on easy work or underpowering hard work.
FAQ
Is Grok 4.5 better than GPT-5.6? On list price and claimed speed, usually yes. On Terminal-Bench 2.1 Sol headline scores, GPT-5.6 leads. On hard SWE-Bench Pro work, Fable 5 leads both.
Is Grok 4.5 cheaper than Claude Fable 5? On published API list rates, yes by a large margin ($2/$6 vs $10/$50). Total project cost still depends on retries and thrashing.
Which should I use as my daily default? If cost and speed dominate: Grok 4.5 or GPT-5.6 Terra. If one-pass hard engineering dominates: Fable 5. Revisit after a week of real traces.
Where to start
- How to use Grok 4.5 for coding — install paths, API, practical tips
- Grok Build vs Claude Code vs Codex — agent CLIs, not just models
- Grok 4.5 / Grok Build from your phone — remote-control a local Grok agent with SeaWork
- Official: Grok 4.5 · Fable 5 · GPT-5.6 Sol