Claude Opus 4.8 (Reasoning, Low)

anthropic/claude-opus-4.8

Claude Opus 4.8 (Reasoning, Low)

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Release Date

May 27th, 2026

Context Size

Reasoning

Yes

Benchmark Cost

$38.34

Speed

64.1 tok/s

Subcategories

Bad Writing Habits

Detects common prose quality anti-patterns in AI-generated creative writing, including passive voice, past progressive overuse, weak dialogue tags, filter words, purple prose, cliches, AI-ism words/adverbs/names, and more.

Scenario	#1	#2	#3	#4	#5	Total
Detailed Writing Rules
Fantasy: entering an ancient ruin Creative Writing Hallucination	91	87	86	86	85	87%
Horror: alone in an eerie place at night Creative Writing Hallucination	94	90	87	87	86	89%
Literary fiction: old friends reunite Creative Writing Hallucination	89	88	88	87	86	88%
Mystery: examining a crime scene Creative Writing Hallucination	92	91	90	88	88	90%
Romance: separated couple reunites Creative Writing Hallucination	90	87	86	85	82	86%
Thriller: chase through city streets Creative Writing Hallucination	93	91	91	89	88	90%
Detailed Writing Rules						88.34%
genre
Fantasy: entering an ancient ruin Creative Writing Hallucination	87	83	79	76	75	80%
Horror: alone in an eerie place at night Creative Writing Hallucination	84	79	79	77	76	79%
Literary fiction: old friends reunite Creative Writing Hallucination	90	86	81	81	79	83%
Mystery: examining a crime scene Creative Writing Hallucination	88	86	84	82	82	84%
Romance: separated couple reunites Creative Writing Hallucination	84	81	81	78	72	79%
Thriller: chase through city streets Creative Writing Hallucination	90	86	83	81	80	84%
genre						81.68%
Novelcrafter Default Prompt
Fantasy: entering an ancient ruin Creative Writing Hallucination	87	84	82	81	79	83%
Horror: alone in an eerie place at night Creative Writing Hallucination	89	87	84	81	79	84%
Literary fiction: old friends reunite Creative Writing Hallucination	86	85	84	84	82	84%
Mystery: examining a crime scene Creative Writing Hallucination	90	89	86	84	83	86%
Romance: separated couple reunites Creative Writing Hallucination	86	85	85	79	78	83%
Thriller: chase through city streets Creative Writing Hallucination	87	86	85	85	83	85%
Novelcrafter Default Prompt						84.24%
84.75%

Codex Extraction

Evaluates a model's ability to extract structured codex entries (characters, locations, objects, lore) from prose passages and return them as well-formed XML.

Scenario	#1	#2	#3	#4	#5	Total
Long: The Spire of Echoes (Dense) Tooling Reasoning	99	99	99	99	98	99%
Medium: The Hollow (Inferred) Tooling Reasoning	100	100	100	99	99	99%
Medium: Through the Thornveil (Scattered) Tooling Reasoning	99	99	99	99	98	99%
Short: The Rusty Lantern (Explicit) Tooling Reasoning	100	100	95	95	95	97%
98.43%

Codex Red Herring (False Positive Detection)

Tests whether models correctly report "no violations" when a codex is fully consistent with the prose passage. Models that hallucinate false violations (false positives) fail. Uses a 2×2 matrix of text length × codex size, with bare and detailed-entry variants.

Scenario	#1	#2	#3	#4	#5	#6	#7	#8	#9	#10	Total
basic entries
Long text (~1594 words), big codex (51 entries) Hallucination	25	25	25	25	25	25	25	25	25	17	24%
Long text (~1594 words), small codex (11 entries) Hallucination	100	100	100	100	100	100	25	25	25	25	70%
Short text (~524 words), big codex (51 entries) Hallucination	100	100	100	100	100	100	100	100	100	100	100%
Short text (~524 words), small codex (11 entries) Hallucination	100	100	100	100	100	100	100	100	100	100	100%
basic entries											73.54%
detailed entries
Long text (~1594 words), big codex (51 detailed entries) Hallucination	100	100	100	100	100	100	100	100	100	100	100%
Long text (~1594 words), small codex (11 detailed entries) Hallucination	100	100	100	100	100	100	100	100	100	100	100%
Short text (~524 words), big codex (51 detailed entries) Hallucination	100	100	100	100	100	100	100	100	25	25	85%
Short text (~524 words), small codex (11 detailed entries) Hallucination	100	100	100	100	100	100	100	100	100	25	93%
detailed entries											94.38%
83.96%

Codex Violation Detection

Detects factual inconsistencies between a story bible and prose passages. The model must output structured XML identifying each violation with paragraph number and substring.

Scenario	#1	#2	#3	#4	#5	#6	#7	#8	#9	#10	Total
matrix
Large codex (40 entries), long passage (1,019 words) Tooling Reasoning	98	97	97	96	96	96	95	95	90	89	95%
Large codex (40 entries), short passage (165 words) Tooling Reasoning	98	98	98	98	98	98	98	96	94	92	97%
Small codex (7 entries), long passage (734 words) Tooling Reasoning	100	100	100	100	100	100	100	100	97	92	99%
Small codex (7 entries), short passage (165 words) Tooling Reasoning	100	100	100	100	100	100	100	100	100	100	100%
matrix											97.68%
tiers
5 codex entries Tooling Reasoning	100	100	100	100	100	100	100	100	100	83	98%
10 codex entries Tooling Reasoning	100	100	100	100	100	100	100	100	100	100	100%
20 codex entries Tooling Reasoning	97	94	94	92	92	89	88	88	85	81	90%
40 codex entries Tooling Reasoning	100	100	100	100	100	100	100	99	92	83	97%
tiers											96.46%
97.07%

Data extraction

Extract key details from a given block of text.

Scenario	#1	#2	#3	#4	#5	#6	#7	#8	#9	#10	Total
All valid emails Utility	100	100	100	100	100	100	100	100	100	100	100%
Contextual pronoun Utility	100	100	100	100	100	100	100	100	100	100	100%
Fruits excluding citrus Utility	100	100	100	100	100	100	100	100	100	100	100%
Future event time Reasoning	50	50	50	50	50	50	50	50	50	50	50%
Guess the pet Reasoning	100	100	100	100	100	100	100	100	100	100	100%
Highest-rated movie Reasoning	100	100	100	100	100	100	100	100	100	100	100%
Indirect birth year Reasoning	100	100	100	100	100	100	100	100	100	100	100%
What instrument does Lucy play? Reasoning	100	100	100	100	100	100	100	100	100	100	100%
What's the color of the car? Utility	100	100	100	100	100	100	100	100	100	100	100%
What's the correct time? Reasoning	0	0	0	0	0	0	0	0	0	0	0%
Who's the sister? Reasoning	100	100	100	100	100	100	100	100	100	100	100%
Who's the tallest? Reasoning	100	100	100	100	100	100	100	100	100	100	100%
87.50%

Dialogue tags

Various tasks related to dialogue tags in text.

Scenario	#1	#2	#3	#4	#5	#6	#7	#8	#9	#10	Total
dialogue-200
Write 200 words with 10% dialogue Rule Following Utility	100	99	98	97	96	94	91	89	88	83	94%
Write 200 words with 50% dialogue Rule Following Utility	55	50	50	50	50	50	50	50	50	50	51%
Write 200 words with 90% dialogue Rule Following Utility	97	89	89	83	83	83	83	83	77	76	84%
dialogue-200											76.12%
dialogue-500
Write 500 words with 30% dialogue Rule Following Utility	67	60	56	53	52	51	50	50	47	10	50%
Write 500 words with 50% dialogue Rule Following Utility	50	50	50	50	50	50	49	47	41	41	48%
Write 500 words with 70% dialogue Rule Following Utility	92	52	50	50	50	50	50	44	41	38	52%
dialogue-500											49.64%
Ungrouped
Write unattributed dialogue Rule Following	100	100	100	100	100	100	100	100	100	100	100%
68.19%

Language Comprehension

Does the model understand more than just English?

Scenario	#1	#2	#3	#4	#5	Total
Asking for directions (Dutch) Language	100	100	100	100	100	100%
Asking for directions (German) Language	100	100	100	100	100	100%
Friend got new kittens (German) Language	100	100	100	100	0	80%
Friend got new kittens (Tagalog) Language	100	100	100	100	100	100%
95.00%

Language Writing

Can the model generate text in different languages?

Scenario	#1	#2	#3	#4	#5	Total
Character dialogue (French) in a story Language	100	100	100	100	100	100%
Character dialogue (German) in a story Language	100	100	100	100	100	100%
Character dialogue (Hindi) in a story Language	100	100	100	100	47	89%
Character dialogue (Italian) in a story Language	100	100	100	100	93	99%
Character dialogue (Spanish) in a story Language	100	100	100	100	100	100%
97.63%

N-Length Sentences

Write sentences with exactly N words

Scenario	#1	#2	#3	#4	#5	#6	#7	#8	#9	#10	Total
Write sentences with 5 words each Utility	100	100	100	100	100	100	100	100	95	95	99%
Write sentences with 10 words each Utility	100	100	100	100	100	100	100	100	100	100	100%
Write sentences with 20 words each Utility	100	100	100	100	100	100	100	100	100	100	100%
99.67%

Novel outline

Handle questions about the outline of a novel in various formats

Scenario	#1	#2	#3	#4	#5	#6	#7	#8	#9	#10	Total
outline-count
Count acts Utility	100	100	100	100	100	100	100	100	100	100	100%
Count chapters Utility	100	100	100	100	100	100	100	100	100	100	100%
Count scenes Utility	100	100	100	100	100	100	100	100	100	100	100%
outline-count											100.00%
pov-count
Count point of views for Jack and Olivia Utility	100	100	100	100	100	100	100	100	50	50	90%
Count point of views for Jack Harper Utility	100	100	100	100	100	100	100	100	100	0	90%
Count point of views for Olivia Utility	100	100	100	100	100	100	100	100	100	100	100%
pov-count											93.33%
96.67%

Text Replacement

Tests deterministic text transformations: renaming characters/locations, expanding contractions, tense rewriting, POV shifts, gender swaps, combined transformations, and word avoidance. Scored by checking each expected change independently.

Scenario	#1	#2	#3	#4	#5	#6	#7	Total
Generic Prompt
Avoid said/asked/replied/answered Text Editing	100	100	100	100	100	100	100	100%
Character rename: Elena->Mirabel, Gregor->Aldric Text Editing	100	100	100	100	100	100	100	100%
Combined: 3rd person past → 1st person present Text Editing	99	99	99	99	99	99	96	99%
Expand all contractions Text Editing	100	100	100	100	100	100	100	100%
Location rename: market square, outer ring, bridge, northern mines Text Editing	100	100	100	100	100	100	100	100%
Multi-character gender swap: Priya(F)->Rohan(M), Mara unchanged Text Editing	100	100	100	100	100	100	100	100%
Passive voice → active voice Text Editing Hallucination	99	98	98	98	98	98	95	98%
POV shift: 3rd person to 1st person (Elena's perspective) Text Editing	100	100	100	100	100	100	100	100%
Tense rewriting: past to present Text Editing	100	99	99	99	99	99	99	99%
Generic Prompt								99.61%
Specific Prompt
Avoid said/asked/replied/answered Text Editing	100	100	100	100	100	100	100	100%
Character rename: Elena->Mirabel, Gregor->Aldric Text Editing	100	100	100	100	100	100	100	100%
Combined: 3rd person past → 1st person present Text Editing	99	98	97	96	96	95	95	96%
Expand all contractions Text Editing	100	100	100	100	100	100	100	100%
Location rename: market square, outer ring, bridge, northern mines Text Editing	100	100	100	100	100	100	100	100%
Multi-character gender swap: Priya(F)->Rohan(M), Mara unchanged Text Editing	100	100	100	100	100	100	100	100%
Passive voice → active voice Text Editing Hallucination	99	99	99	99	99	98	98	99%
POV shift: 3rd person to 1st person (Elena's perspective) Text Editing	100	100	100	100	100	100	100	100%
Tense rewriting: past to present Text Editing	100	100	100	100	100	99	99	100%
Specific Prompt								99.48%
99.54%

Tool usage within Novelcrafter

Output messages that are related to tool usage within Novelcrafter

Scenario	#1	#2	#3	#4	#5	#6	#7	#8	#9	#10	Total
Create alternate prose sections Tooling	100	100	100	100	100	100	100	100	100	100	100%
100.00%

Voice/dialogue sheets

Extract dialogue from given text as voice sheets.

Scenario	#1	#2	#3	#4	#5	#6	#7	#8	#9	#10	Total
Multiple speakers Rule Following	100	100	100	100	100	100	100	100	100	100	100%
Simple Rule Following	100	100	100	100	100	100	100	100	100	100	100%
Simple (1-shot) 1-shot Rule Following	100	100	100	100	100	100	100	100	100	100	100%
Simple (5-shot) Few-shot Rule Following	100	100	100	100	100	100	100	100	100	100	100%
Unattributed dialogue Rule Following	100	0	0	0	0	0	0	0	0	0	10%
82.00%

Write N of X

Write exactly N words/sentences/paragraphs...

Scenario	#1	#2	#3	#4	#5	#6	#7	#8	#9	#10	Total
paragraphs
1 paragraph summary Utility	100	100	100	100	100	100	100	100	100	100	100%
3 paragraph summary Utility	100	100	100	100	100	100	100	100	100	100	100%
5 paragraph summary Utility	100	100	100	100	100	100	100	100	100	100	100%
paragraphs											100.00%
sentences
1 sentence summary Utility	100	100	100	100	100	100	100	100	100	100	100%
3 sentence summary Utility	100	100	100	100	100	100	100	100	100	100	100%
10 sentence summary Utility	100	100	100	100	100	100	100	100	100	100	100%
20 sentence summary Utility	100	100	100	100	100	100	100	100	98	98	100%
50 sentence summary Utility	100	100	100	100	100	100	98	98	77	54	93%
sentences											98.48%
words
10 word summary Utility	100	100	100	100	100	100	100	100	100	100	100%
20 word summary Utility	100	100	100	100	100	100	100	98	98	54	95%
50 word summary Utility	100	100	100	100	100	100	100	100	98	92	99%
100 word summary Utility	100	100	100	100	100	100	98	98	98	77	97%
200 word summary Utility	100	100	100	100	100	100	98	77	77	77	93%
words											96.85%
98.20%