Claude Sonnet 4.5

anthropic/claude-sonnet-4.5

Claude Sonnet 4.5

via OpenRouter

Release Date

Sep 29th, 2025

Context Size

Reasoning

Benchmark Cost

$13.53

Speed

56.5 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	88	87	87	82	87%
Horror: alone in an eerie place at night Creative Writing Hallucination	92	92	89	89	83	89%
Literary fiction: old friends reunite Creative Writing Hallucination	90	90	86	83	82	86%
Mystery: examining a crime scene Creative Writing Hallucination	94	91	89	88	88	90%
Romance: separated couple reunites Creative Writing Hallucination	94	90	88	87	83	88%
Thriller: chase through city streets Creative Writing Hallucination	94	90	89	89	87	90%
Detailed Writing Rules						88.39%
genre
Fantasy: entering an ancient ruin Creative Writing Hallucination	83	81	79	75	68	77%
Horror: alone in an eerie place at night Creative Writing Hallucination	85	80	79	77	73	79%
Literary fiction: old friends reunite Creative Writing Hallucination	86	82	82	78	77	81%
Mystery: examining a crime scene Creative Writing Hallucination	87	85	84	84	82	85%
Romance: separated couple reunites Creative Writing Hallucination	89	82	80	78	72	80%
Thriller: chase through city streets Creative Writing Hallucination	91	87	84	84	81	85%
genre						81.16%
Novelcrafter Default Prompt
Fantasy: entering an ancient ruin Creative Writing Hallucination	78	75	74	72	72	74%
Horror: alone in an eerie place at night Creative Writing Hallucination	90	89	85	82	82	86%
Literary fiction: old friends reunite Creative Writing Hallucination	88	85	84	82	79	84%
Mystery: examining a crime scene Creative Writing Hallucination	89	82	81	81	81	83%
Romance: separated couple reunites Creative Writing Hallucination	92	83	83	80	79	83%
Thriller: chase through city streets Creative Writing Hallucination	87	86	84	83	83	85%
Novelcrafter Default Prompt						82.41%
83.99%

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	96	95	95	95	95	95%
Medium: The Hollow (Inferred) Tooling Reasoning	97	97	96	96	96	96%
Medium: Through the Thornveil (Scattered) Tooling Reasoning	98	98	97	97	96	97%
Short: The Rusty Lantern (Explicit) Tooling Reasoning	100	100	100	99	99	99%
96.97%

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	35	33	33	32	32	32	8	7	7	6	23%
Long text (~1594 words), small codex (11 entries) Hallucination	35	35	33	33	33	33	33	32	32	10	31%
Short text (~524 words), big codex (51 entries) Hallucination	100	25	25	25	25	25	17	17	17	17	29%
Short text (~524 words), small codex (11 entries) Hallucination	100	100	42	25	25	25	25	25	17	17	40%
basic entries											30.72%
detailed entries
Long text (~1594 words), big codex (51 detailed entries) Hallucination	100	100	42	42	38	38	38	33	17	17	46%
Long text (~1594 words), small codex (11 detailed entries) Hallucination	33	8	8	8	8	7	7	7	7	6	10%
Short text (~524 words), big codex (51 detailed entries) Hallucination	25	25	17	17	17	17	17	13	13	13	17%
Short text (~524 words), small codex (11 detailed entries) Hallucination	25	25	17	17	17	17	17	17	13	10	17%
detailed entries											22.68%
26.70%

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	93	92	91	90	89	89	87	87	85	85	89%
Large codex (40 entries), short passage (165 words) Tooling Reasoning	100	100	100	100	100	100	100	100	100	100	100%
Small codex (7 entries), long passage (734 words) Tooling Reasoning	100	97	92	92	92	88	88	83	83	83	90%
Small codex (7 entries), short passage (165 words) Tooling Reasoning	100	100	100	100	100	100	100	100	100	100	100%
matrix											94.66%
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	100	100	100	100	100	100	92	92	92	92	97%
40 codex entries Tooling Reasoning	100	100	100	100	100	100	100	100	100	92	99%
tiers											98.62%
96.64%

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	97	96	91	86	82	80	80	76	52	84%
Write 200 words with 50% dialogue Rule Following Utility	55	50	26	14	10	10	7	5	1	0	18%
Write 200 words with 90% dialogue Rule Following Utility	75	57	53	50	50	50	49	49	47	36	52%
dialogue-200											51.12%
dialogue-500
Write 500 words with 30% dialogue Rule Following Utility	42	37	19	11	6	5	1	0	0	0	12%
Write 500 words with 50% dialogue Rule Following Utility	48	46	46	30	13	1	0	0	0	0	18%
Write 500 words with 70% dialogue Rule Following Utility	46	42	37	18	17	16	1	0	0	0	18%
dialogue-500											16.07%
Ungrouped
Write unattributed dialogue Rule Following	100	100	100	100	100	100	100	100	100	100	100%
43.08%

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	95	94	93	96%
Character dialogue (Hindi) in a story Language	62	53	50	50	47	52%
Character dialogue (Italian) in a story Language	100	100	100	100	100	100%
Character dialogue (Spanish) in a story Language	100	100	100	100	100	100%
89.77%

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	99	96	94	91	89	86	95%
Write sentences with 10 words each Utility	100	100	100	100	100	100	98	97	90	87	97%
Write sentences with 20 words each Utility	92	72	69	65	59	58	49	42	20	2	53%
81.87%

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	0	0	80%
outline-count											93.33%
pov-count
Count point of views for Jack and Olivia Utility	100	100	100	100	50	50	0	0	0	0	50%
Count point of views for Jack Harper Utility	100	100	100	100	100	100	100	100	100	100	100%
Count point of views for Olivia Utility	100	100	100	100	100	0	0	0	0	0	50%
pov-count											66.67%
80.00%

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	99	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	98	97	96	96	96	96	95	96%
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	100	99	100%
Generic Prompt								99.46%
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	100	99	99	99	99	99	99	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	100	99	99	99	98	98	97	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	100	100	100%
Specific Prompt								99.77%
99.62%

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	0	0	80%
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	100	100	100	0	0	0	0	0	0	40%
84.00%

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	92	99%
20 sentence summary Utility	100	100	98	98	98	98	98	92	92	92	97%
50 sentence summary Utility	98	98	98	98	77	77	54	27	9	0	64%
sentences											91.98%
words
10 word summary Utility	100	100	100	100	100	100	100	100	100	100	100%
20 word summary Utility	100	98	98	92	92	92	92	77	77	54	87%
50 word summary Utility	100	100	100	100	100	98	77	77	27	0	78%
100 word summary Utility	100	100	98	77	77	27	9	9	0	0	50%
200 word summary Utility	100	100	100	98	92	54	9	2	0	0	55%
words											74.15%
86.97%