Is Claude Opus 5.5 better overall than Fable 5.1 and GPT-6 Astra?

Overall, yes, and it still is as of November 6, 2026: on the re-based Artificial Analysis Intelligence Index v5.0.1, Opus 5.5 scores 59 at max effort against 57 for GPT-6 Astra (max) and 49 for Claude Fable 5.1 (max; 50 at xhigh), at $4/$20 per million tokens against $10/$50 for the other two. (On the earlier index version, read October 16, the scores were 58, 53 and 53.) Against Astra specifically, Opus 5.5 leads Terminal-Bench 4.0 (66.4% vs 57.9% on Anthropic's table; Artificial Analysis measures them level at 59.6%), FrontierCode v1.1 (54.4% vs 53.3%), GDPval-AA v2.1 (1846 vs 1542 Elo) and Humanity's Last Exam (67.7% vs 57.2%), and leads Astra on the AA Intelligence Index (59 vs 57 on v5.0.1). GPT-6 Astra leads AutomationBench (41.4% vs 40.0%), Terminal-Bench-Science (64.6% vs 58.7%), and computer use per OpenAI, and uses far fewer output tokens per task, which makes it cheaper per AA task at max effort ($6.24 vs $10.04 on AA's November 2026 figures). Fable 5.1 trails Opus 5.5 on every row of Anthropic's table but remains the safer max-effort pick.

Opus 5.5 vs Fable 5.1: which should I use?

Use Opus 5.5 by default. Anthropic's own table shows it beating Fable 5.1 on every listed benchmark at 40% of the price ($4/$20 vs $10/$50), and as of November 6, 2026 Artificial Analysis scores it 59 versus 49 for Fable 5.1 at max effort (50 at xhigh) on Intelligence Index v5.0.1. It is also cheaper per AA task at max effort: $10.04 versus $12.99. Fable 5.1 keeps two advantages: cache reads at $0.25 are nearly as cheap, and it did not over-think on Simon Willison's max-effort test where Opus 5.5 twice hit its 128K output limit. Anthropic says the real-world gap is narrower than the scores suggest, and Fable 5.1 remains the flagship for Max and Team Premium subscribers.

Which frontier model is cheapest per task in September 2026?

It depends on effort. Artificial Analysis puts four of Opus 5.5's five effort levels (medium, high, xhigh, max) on the intelligence-versus-cost Pareto frontier for models scoring 50+, ahead of GPT-6 Astra, Fable 5.1 and Opus 5. Anthropic says Opus 5.5 at default effort matches Astra on Terminal-Bench 4.0 for about 40% of the cost and beats Astra at max on GDPval for about a fifth of the cost. GPT-6 Astra's advantage is token efficiency: roughly 27,000 output tokens per AA task at max versus 119,000 for Opus 5.5 and 78,000 for Fable 5.1, so at high effort settings Astra's higher list price is partly offset. November 2026 update: after Artificial Analysis moved to Intelligence Index v5.0.1, cost per index task at max effort is $10.04 for Opus 5.5 (score 59), $12.99 for Fable 5.1 (49) and $6.24 for Astra (57); the cheapest near-top run is GPT-6.1 Sol (released September 29 at $2/$10), which scores 55 at max for $1.27 a task. On the October 16 index the figures were $5.98, $7.63 and $3.26, with GPT-6.1 Sol at 52 for $0.72.

Do Claude Opus 5.5 and Fable 5.1 share the same safeguards?

Largely yes. Because Opus 5.5 matches Claude Mythos 5.1 in biology and cybersecurity, it ships with Fable 5.1-class safeguards: most offensive-security tasks fall back transparently to Opus 4.8, biology and frontier-LLM-development tasks fall back to Opus 5, and preserved thinking blocks API users from editing prior context on accounts created on or after August 31, 2026. As of October 2026 both the Life Sciences Verification Program and the updated Cyber Verification Program, which now covers Opus 5.5, Sonnet 5.5 and Mythos 5.1, take applications through Anthropic's Verification Portal. GPT-6 Astra has its own Trusted Access tiers for cyber use.

Quick Answer

Claude Opus 5.5 vs Fable 5.1 vs GPT-6 Astra (Nov 2026)

Published: September 23, 2026 • Updated: November 6, 2026

The short answer

Claude Opus 5.5 is the new default frontier pick. Released September 22, 2026 at $4/$20 per million tokens, it outscores both $10/$50 flagships, Claude Fable 5.1 and GPT-6 Astra, on most published benchmarks and, as of November 6, 2026, leads both on the Artificial Analysis Intelligence Index v5.0.1: 59 at max effort versus 57 for Astra and 49 for Fable 5.1. Only Google’s Gemini 4 Carbon (60), which is not yet publicly available, scores higher. GPT-6 Astra still wins on business-workflow automation, scientific terminal work, computer use and token efficiency; Fable 5.1 wins on nothing decisive any more but remains a safer bet for max-effort runs. If you were choosing between the two $10/$50 models before September 22, the answer since then is usually neither.

Is Opus 5.5 better overall than Fable 5.1 and GPT-6 Astra? Yes, still, as of November 6, 2026: it scores 59 on the Artificial Analysis Intelligence Index v5.0.1 against 57 for Astra and 49 for Fable 5.1, at 40% of their list price. Astra keeps automation, science, computer use and cost per task at max effort; Fable 5.1 keeps max-effort reliability.

Opus 5.5 vs Fable 5.1: pick Opus 5.5. It beats Fable 5.1 on every row of Anthropic’s benchmark table, scores 59 versus 49 on the current AA index, costs $4/$20 against $10/$50 and is cheaper per AA task even at max effort ($10.04 vs $12.99). Keep Fable 5.1 only for single-shot max-effort runs where Opus 5.5 has been seen to exhaust its output budget.

What changed as of November 2026

Artificial Analysis re-based its index. Intelligence Index v5.0.1 (nine evaluations, including FrontierCode 2.0 and HLE-Diamond) gives Opus 5.5 59 at max, GPT-6 Astra 57 at max and Fable 5.1 49 at max (50 at xhigh). Scores on v5.0.1 are not comparable with the 58/53/53 we quoted in October. The gap between Opus 5.5 and Astra narrowed; the gap to Fable 5.1 widened.
Cost per AA task rose with the new evaluations: $10.04 for Opus 5.5, $12.99 for Fable 5.1 and $6.24 for Astra at max effort. Astra is still the cheapest of the three per task at max; Opus 5.5 at high effort scores 52 for $3.46.
Prices unchanged. Anthropic’s pricing page on November 6 still lists Opus 5.5 at $4/$20 ($0.20 cache hits) and Fable 5.1 at $10/$50 ($0.25); OpenAI’s still lists gpt-6-astra at $10/$50, $1.00 cached, $20/$75 above 272K input tokens.
A new top score, not yet usable. Google announced Gemini 4 Carbon on October 28 (AA v5.0.1: 60 at high effort). It is limited to cyber defenders and trusted partners through Google’s Fairwind Program; Google says it will launch at Argon’s introductory $2/$10 but gives no public date. See what Gemini 4 Carbon is.
OpenAI added models below and beside Astra, not above it. GPT-6.1 Terra (October 26, $1/$5) scores 51 at max; GPT-6 Cyber, an Astra variant for authorised vulnerability research, is priced at $20/$100 for approved Daybreak customers. There is still no GPT-6.1 Astra. See what GPT-6.1 Terra is.

What changed as of October 2026

The three-way ranking above has held for three weeks; the field around it moved:

Prices unchanged. Anthropic’s pricing page still lists Opus 5.5 at $4/$20 (cache hits $0.20) and Fable 5.1 at $10/$50 (cache hits $0.25); OpenAI’s still lists gpt-6-astra at $10/$50 with $1.00 cached input and $20/$75 above 272K input tokens.
No Astra successor. OpenAI shipped GPT-6.1 Sol on September 29 ($2/$10, cached input $0.10) but no GPT-6.1 Astra; the release was reported cancelled, and GPT-6 Astra is still OpenAI’s flagship. See why OpenAI cancelled GPT-6.1 Astra.
Cheaper Claude near the top. Claude Sonnet 5.5 (September 28, $2/$10) scores 56 on the AA index at max effort, second only to Opus 5.5; Claude Haiku 5.5 followed on October 7 at $0.10 input / $0.50 output per million tokens for prompts up to 100K tokens. See Sonnet 5.5 vs Opus 5.5.
Two new frontier rivals. Google’s Gemini 4 Argon went generally available on October 13 at an introductory $2/$10 through November 30, scoring 53 at high effort, level with Astra and Fable 5.1 (Argon vs Opus 5.5 vs Astra). Meta’s Muse Wonder ($4/$20) scores 52, and Muse Wonder Full 56.
Cyber access opened. The updated Cyber Verification Program now covers Opus 5.5, Sonnet 5.5 and Mythos 5.1 and takes applications through Anthropic’s Verification Portal.

Side by side

	Claude Opus 5.5	Claude Fable 5.1	GPT-6 Astra
Released	September 22, 2026	September 3, 2026	September 3, 2026
Price (in / out per MTok)	$4 / $20	$10 / $50	$10 / $50
Cache read	$0.20	$0.25	$1.00
Context / max output	1M / 128K	1M / 128K	1.05M / 128K
Long-prompt repricing	None	None	>272K input: 2x input, 1.5x output
Knowledge cutoff	June 2026	June 2026	April 30, 2026
Default effort	medium	high	medium
Thinking	Adaptive, always on	Adaptive, always on	Reasoning effort none → max
AA Intelligence Index v5.0.1 (max, Nov 6, 2026)	59	49 (50 at xhigh)	57
AA cost per index task (max effort, Nov 6, 2026)	$10.04	$12.99	$6.24
Output tokens per AA task (max, Sep 2026 index)	~119K	~78K	~27K
Clouds	Anthropic, AWS, GCP, Azure	Anthropic, AWS, GCP, Azure	OpenAI, Azure, AWS (staged)
Cyber / bio gating	Fable-class safeguards, verification programs	Same	Trusted Access tiers

Benchmarks

Anthropic’s launch table (Opus 5.5 at max effort; Astra figures as reported by OpenAI):

Benchmark	Opus 5.5	Fable 5.1	GPT-6 Astra	Leader
Terminal-Bench 4.0	66.4%	55.8%	57.9%	Opus 5.5
FrontierCode v1.1 (Main)	54.4%	50.3%	53.3%	Opus 5.5
CursorBench 4.0	57.8%	51.8%	—	Opus 5.5
GDPval-AA v2.1 (Elo)	1846	1735	1542	Opus 5.5
AutomationBench (Zapier)	40.0%	31.4%	41.4%	Astra
Humanity’s Last Exam (tools)	67.7%	65.6%	57.2%	Opus 5.5
Terminal-Bench-Science 0.1	58.7%	52.6%	64.6%	Astra
OSWorld 2.0 (partial)	81.8%	80.7%	—	Opus 5.5 (Astra not listed)

Independent cross-check from Artificial Analysis: Opus 5.5 leads six of the ten Intelligence Index evaluations (HLE 61.4%, SciCode 66.9%, GDPval-AA, AA-Briefcase 1,822 Elo, AA-Omniscience, AutomationBench-AA); Terminal-Bench 4.0 is a tie with Astra at 59.6%; Opus 5.5 trails on CritPt, AA-LCR and GDP.pdf. OpenAI still describes Astra as “the world’s best model for computer use,” and Anthropic’s OSWorld row omits Astra, so treat computer use as Astra’s unless you benchmark your own tasks.

Two caveats on Anthropic’s numbers: Opus 5.5 was evaluated with production safeguards on, with cyber tasks falling back to Opus 4.8 and biology tasks to Opus 5, which Anthropic says likely lowers its scores; and Zapier’s AutomationBench run counted safeguard interventions as failures.

Cost per task, not per token

List price says Opus 5.5 is 60% cheaper than the flagships. Reality depends on how many tokens each model burns:

Opus 5.5 at max uses ~119K output tokens per AA task, 1.5x Fable 5.1 and 4.4x Astra. At max, its cost advantage over Fable 5.1 mostly holds (cheaper tokens), but against Astra it shrinks.
Opus 5.5 at medium (the default) is where Anthropic’s claims live: it matches Astra on Terminal-Bench 4.0 for about 40% of the cost, beats Astra on FrontierCode at roughly 20% of the cost per task, and beats Astra at max on GDPval for about a fifth of the cost.
Astra’s 272K threshold doubles input pricing on very long prompts; neither Claude model reprices. For 500K-token codebases, that alone can flip the comparison.
Cache reads: Opus 5.5 $0.20, Fable 5.1 $0.25, Astra $1.00. On agent loops where 90% of input is cached, Astra’s effective input price is roughly 4x the Claude models’.

Simon Willison’s max-effort warning applies: Opus 5.5 at max twice consumed its entire 128K output budget reasoning about an SVG and returned nothing, at $2.56 per attempt; Fable 5.1 at max produced his best-ever result. Run Opus 5.5 at medium or high unless you have measured otherwise.

Which to pick

Use case	Pick	Why
Agentic coding, migrations, terminal work	Opus 5.5	Leads Terminal-Bench 4.0, FrontierCode, CursorBench at 40% of the price
Reports, financial models, decks	Opus 5.5	GDPval +111 Elo over Fable, +304 over Astra; 16/18 fact-checked reports passed
Zapier-style multi-app business workflows	GPT-6 Astra (or GPT-6 Sol for cost)	AutomationBench 41.4% vs 40.0%; see GPT-6 Sol vs Luna vs Astra
Scientific research agents	GPT-6 Astra	Terminal-Bench-Science 64.6% vs 58.7%
Computer-use agents	Astra, test Opus 5.5	OpenAI claims the lead; Opus 5.5 posts 81.8% OSWorld partial
Max-effort, single-shot hard problems	Fable 5.1	Did not over-think to failure in independent testing
Long-context (>272K) prompts	Opus 5.5 or Fable 5.1	No repricing threshold
Near-frontier work at half the price (Nov 2026)	Claude Sonnet 5.5 or GPT-6.1 Sol	Both $2/$10; both score 55 at max on AA v5.0.1, and GPT-6.1 Sol costs $1.27 per AA task against $10.02 for Sonnet 5.5
Offensive security research	Whichever program admits you	All three gate cyber behind verification/trusted access

Bottom line

For the first time, Anthropic’s mid-priced Opus is also its best-scoring model on most axes, and the $10/$50 tier has become a niche: Fable 5.1 for max-effort reliability, Astra for automation, science and computer use. Anthropic itself says “the gap between Opus 5.5 and Claude Fable 5.1 is narrower than these scores suggest,” so expect Fable 5.1 users to feel a smaller difference than the table implies. The practical move is to route default traffic to Opus 5.5 at medium effort and keep one flagship in the router for the workloads above.

Last verified: November 6, 2026. Benchmark tables are from the September 22 launch materials; prices, the AA index (now v5.0.1) and per-task costs were re-checked on November 6, 2026. Output tokens per task are from the September index and were not re-measured.